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Diffstat (limited to 'fs/eventpoll.c')
| -rw-r--r-- | fs/eventpoll.c | 3030 |
1 files changed, 3030 insertions, 0 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c new file mode 100644 index 000000000..e0c4bf88a --- /dev/null +++ b/fs/eventpoll.c @@ -0,0 +1,3030 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * fs/eventpoll.c (Efficient event retrieval implementation) + * Copyright (C) 2001,...,2009 Davide Libenzi + * + * Davide Libenzi <davidel@xmailserver.org> + */ + +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/sched/signal.h> +#include <linux/fs.h> +#include <linux/file.h> +#include <linux/signal.h> +#include <linux/errno.h> +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/poll.h> +#include <linux/string.h> +#include <linux/list.h> +#include <linux/hash.h> +#include <linux/spinlock.h> +#include <linux/syscalls.h> +#include <linux/rbtree.h> +#include <linux/wait.h> +#include <linux/eventpoll.h> +#include <linux/mount.h> +#include <linux/bitops.h> +#include <linux/mutex.h> +#include <linux/anon_inodes.h> +#include <linux/device.h> +#include <linux/uaccess.h> +#include <asm/io.h> +#include <asm/mman.h> +#include <linux/atomic.h> +#include <linux/proc_fs.h> +#include <linux/seq_file.h> +#include <linux/compat.h> +#include <linux/rculist.h> +#include <linux/capability.h> +#include <linux/seqlock.h> +#include <net/busy_poll.h> + +/* + * fs/eventpoll.c - Efficient event polling ("epoll") kernel implementation. + * + * + * Overview + * -------- + * + * Each epoll_create(2) returns an anonymous [eventpoll] file whose + * ->private_data is a struct eventpoll. Each EPOLL_CTL_ADD installs + * a struct epitem linking one (watched file, fd) pair back to that + * eventpoll via the watched file's f_op->poll() wait queue(s). When + * the watched file signals readiness, ep_poll_callback() fires and + * marks the epitem ready. epoll_wait(2) drains the ready list under + * ep->mtx, re-queueing items in level-triggered mode. + * + * epoll instances can watch other epoll instances up to EP_MAX_NESTS + * deep; cycles are forbidden and detected at EPOLL_CTL_ADD time. + * + * + * Locking + * ------- + * + * Three levels, acquired from outer to inner: + * + * epnested_mutex (global; rare; taken only for EPOLL_CTL_ADD + * loop / path checks) + * > ep->mtx (per-eventpoll; sleepable; serializes most ops) + * > ep->lock (per-eventpoll; IRQ-safe spinlock) + * + * file->f_lock (per-file; NOT IRQ-safe; guards f_ep hlist ops; + * nested inside ep->mtx, outside ep->lock) + * + * Rationale: + * - ep->lock is a spinlock because ep_poll_callback() is called from + * wake_up() which may run in hard-IRQ context. All ep->lock + * critical sections use spin_lock_irqsave(). + * - ep->mtx is a sleepable mutex because the event delivery loop + * calls copy_to_user(), and ep_insert() may sleep in + * kmem_cache_alloc() and f_op->poll(). + * - epnested_mutex is global because cycle detection needs a global + * view of the epoll topology; a per-object scheme would let two + * concurrent inserts (A into B, B into A) construct a cycle + * without either observer seeing it. + * - Per-ep ep->mtx is preferred for scalability elsewhere. Events + * that require epnested_mutex are rare. + * + * When EPOLL_CTL_ADD nests one eventpoll inside another we acquire + * ep->mtx on both: outer first, target second. Since cycles are + * forbidden the set of live ep->mtx holds is always a strict chain, + * communicated to lockdep via mutex_lock_nested() subclasses derived + * from the current recursion depth. + * + * + * Field protection + * ---------------- + * + * struct eventpoll: + * mtx - self + * rbr - ep->mtx + * ovflist, rdllist - ep->lock (IRQ-safe) + * wq - ep->lock for queue mutation + * poll_wait - internal waitqueue spinlock + * refs - file->f_lock for adds; ep->mtx for removes; + * RCU for readers (hlist_del_rcu + kfree_rcu(ep)) + * ws - ep->mtx + * gen, loop_check_depth - epnested_mutex + * file, user - immutable after setup + * refcount - atomic (refcount_t) + * napi_* - READ_ONCE / WRITE_ONCE + * + * struct epitem: + * rbn / rcu union - rbn: ep->mtx (while epi is linked in ep->rbr). + * rcu: written only by kfree_rcu(epi) on the free + * path; otherwise untouched by epoll code. + * rdllink, next - ep->lock + * ffd, ep - immutable after ep_insert() + * pwqlist - ep->mtx for writes; POLLFREE clears pwq->whead + * via smp_store_release(), see below + * fllink - file->f_lock for mutation; hlist_del_rcu + + * kfree_rcu(epi) for safe RCU readers + * ws - RCU (rcu_assign_pointer / + * rcu_dereference_check(mtx)) + * event - ep->mtx for writes; lockless read in + * ep_poll_callback pairs with smp_mb() in + * ep_modify() + * + * + * Ready-list state machine + * ------------------------ + * + * Readiness is tracked in two lists under ep->lock: + * + * rdllist - doubly-linked FIFO; the "current" ready list. + * ovflist - singly-linked LIFO; used during a scan to catch + * events that arrive while rdllist is being iterated + * without ep->lock. + * + * Encoded in ep->ovflist: + * EP_UNACTIVE_PTR - no scan active; callback appends to rdllist. + * NULL - scan active, no spill yet. + * pointer to epi - scan active with spilled items (LIFO). + * + * Encoded in epi->ovflist_next: + * EP_UNACTIVE_PTR - epi is not on ovflist. + * otherwise - next epi on ovflist (NULL at tail). + * + * ep_start_scan() flips "not scanning" to "scanning" and splices + * rdllist into a caller-local scan_batch. ep_done_scan() drains ovflist + * back to rdllist (list_add head-insert reverses LIFO to FIFO), + * flips back to "not scanning", and re-splices any items the caller + * left in scan_batch (e.g., level-triggered re-queues). + * + * + * Removal paths + * ------------- + * + * Three paths dispose of epitems and/or eventpolls: + * + * A. ep_remove() - EPOLL_CTL_DEL and ep_insert() + * rollback. Caller holds ep->mtx. + * B. ep_clear_and_put() - close of the epoll fd itself + * (ep_eventpoll_release). + * C. eventpoll_release_file() - close of a watched file, invoked + * from __fput(). + * + * Coordination: + * A and C exclude each other via the watched file's refcount. + * A pins the file with epi_fget() before touching file->f_ep or + * file->f_lock; if the pin fails, __fput() is in flight and C + * will clean this epi up. See the epi_fget() block comment. + * A and B both hold ep->mtx serially. B walks the rbtree with + * rb_next() captured before ep_remove() erases the current node. + * B and C both take ep->mtx; the loser sees fewer entries or an + * empty file->f_ep. + * + * Within every path the internal order is strict: + * ep_unregister_pollwait() - drain pwqlist; synchronizes with any + * in-flight ep_poll_callback via the + * watched wait-queue head's lock. + * ep_remove_file() - hlist_del_rcu of epi->fllink and, + * if last watcher, clear file->f_ep, + * under file->f_lock. + * ep_remove_epi() - rb_erase, rdllist unlink (ep->lock), + * wakeup_source_unregister, + * kfree_rcu(epi). + * + * kfree_rcu(epi) defers the free past RCU readers in + * reverse_path_check_proc(); kfree_rcu(ep) defers past readers in + * ep_get_upwards_depth_proc(). + * + * + * POLLFREE handshake + * ------------------ + * + * When a subsystem tears down a wait-queue head that an epitem is + * registered on (binder, signalfd, ...), it wakes the callback with + * POLLFREE and must RCU-defer the head's free. The store/load pair: + * + * ep_poll_callback() POLLFREE branch: + * smp_store_release(&pwq->whead, NULL) + * + * ep_remove_wait_queue(): + * smp_load_acquire(&pwq->whead) + * + * See those sites for the full argument. + */ + +/* Epoll private bits inside the event mask */ +#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE) + +#define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT) + +#define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \ + EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE) + +/* Maximum number of nesting allowed inside epoll sets */ +#define EP_MAX_NESTS 4 + +#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) + +#define EP_UNACTIVE_PTR ((void *) -1L) + +#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry)) + +/* Wait structure used by the poll hooks */ +struct eppoll_entry { + /* List header used to link this structure to the "struct epitem" */ + struct eppoll_entry *next; + + /* The "base" pointer is set to the container "struct epitem" */ + struct epitem *base; + + /* + * Wait queue item that will be linked to the target file wait + * queue head. + */ + wait_queue_entry_t wait; + + /* The wait queue head that linked the "wait" wait queue item */ + wait_queue_head_t *whead; +}; + +/* + * Each file descriptor added to the eventpoll interface will + * have an entry of this type linked to the "rbr" RB tree. + * Avoid increasing the size of this struct, there can be many thousands + * of these on a server and we do not want this to take another cache line. + */ +struct epitem { + union { + /* RB tree node links this structure to the eventpoll RB tree */ + struct rb_node rbn; + /* Used to free the struct epitem */ + struct rcu_head rcu; + }; + + /* Link on the owning eventpoll's ready list (ep->rdllist). */ + struct list_head rdllink; + + /* + * Link on the owning eventpoll's scan-overflow list (ep->ovflist), + * EP_UNACTIVE_PTR when not linked. See epi_on_ovflist() / + * epi_clear_ovflist() and the "Ready-list state machine" section + * in the top-of-file banner. + */ + struct epitem *ovflist_next; + + /* The file descriptor information this item refers to */ + struct epoll_key ffd; + + /* List containing poll wait queues */ + struct eppoll_entry *pwqlist; + + /* The "container" of this item */ + struct eventpoll *ep; + + /* List header used to link this item to the "struct file" items list */ + struct hlist_node fllink; + + /* wakeup_source used when EPOLLWAKEUP is set */ + struct wakeup_source __rcu *ws; + + /* The structure that describe the interested events and the source fd */ + struct epoll_event event; +}; + +/* + * This structure is stored inside the "private_data" member of the file + * structure and represents the main data structure for the eventpoll + * interface. + */ +struct eventpoll { + /* + * This mutex is used to ensure that files are not removed + * while epoll is using them. This is held during the event + * collection loop, the file cleanup path, the epoll file exit + * code and the ctl operations. + */ + struct mutex mtx; + + /* Wait queue used by sys_epoll_wait() */ + wait_queue_head_t wq; + + /* Wait queue used by file->poll() */ + wait_queue_head_t poll_wait; + + /* List of ready file descriptors */ + struct list_head rdllist; + + /* Lock which protects rdllist and ovflist */ + spinlock_t lock; + + /* Protect switching between rdllist and ovflist */ + seqcount_spinlock_t seq; + + /* RB tree root used to store monitored fd structs */ + struct rb_root_cached rbr; + + /* + * This is a single linked list that chains all the "struct epitem" that + * happened while transferring ready events to userspace w/out + * holding ->lock. + */ + struct epitem *ovflist; + + /* wakeup_source used when ep_send_events or __ep_eventpoll_poll is running */ + struct wakeup_source *ws; + + /* The user that created the eventpoll descriptor */ + struct user_struct *user; + + struct file *file; + + /* used to optimize loop detection check */ + u64 gen; + struct hlist_head refs; + u8 loop_check_depth; + + /* usage count, orchestrates "struct eventpoll" disposal */ + refcount_t refcount; + + /* used to defer freeing past ep_get_upwards_depth_proc() RCU walk */ + struct rcu_head rcu; + +#ifdef CONFIG_NET_RX_BUSY_POLL + /* used to track busy poll napi_id */ + unsigned int napi_id; + /* busy poll timeout */ + u32 busy_poll_usecs; + /* busy poll packet budget */ + u16 busy_poll_budget; + bool prefer_busy_poll; +#endif + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + /* tracks wakeup nests for lockdep validation */ + u8 nests; +#endif +}; + +/* Wrapper struct used by poll queueing */ +struct ep_pqueue { + poll_table pt; + struct epitem *epi; +}; + +/* + * Configuration options available inside /proc/sys/fs/epoll/ + */ +/* Maximum number of epoll watched descriptors, per user */ +static long max_user_watches __read_mostly; + +/* + * Cycle and path-length checks at EPOLL_CTL_ADD + * --------------------------------------------- + * + * When EPOLL_CTL_ADD creates a link that either targets an eventpoll + * file or extends an existing chain of eventpolls, two checks run: + * + * 1. no cycle is being formed -- ep_loop_check() walks downward + * from the candidate target, and ep_get_upwards_depth_proc() + * walks upward from the outer ep, both bounded by EP_MAX_NESTS. + * 2. no file accumulates more than path_limits[depth] wakeup paths + * of a given length -- reverse_path_check(). + * + * Both need a global view of the epoll topology and must be atomic + * with the insertion, so the check is serialized by epnested_mutex + * and carries its scratch state on a stack-allocated struct + * ep_ctl_ctx scoped to one do_epoll_ctl() call. Non-nested inserts + * skip this machinery entirely and take only ep->mtx. + * + * epnested_mutex Serializes the whole check. + * loop_check_gen Global monotonic stamp, bumped at the start of + * a check and again at the end. ep->gen caches + * the value under which ep was last visited by + * ep_loop_check_proc() or + * ep_get_upwards_depth_proc(); the post-check + * bump ensures those cached stamps can no longer + * equal loop_check_gen, so the + * "ep->gen == loop_check_gen" trigger in + * ep_ctl_lock() only fires while another check + * is in flight. + * + * struct ep_ctl_ctx carries the rest (inserting_into, tfile_check_list, + * path_count[]) through the walk; see its declaration below. + * + * Commits fdcfce93073d ("eventpoll: Fix integer overflow in + * ep_loop_check_proc()") and f2e467a48287 ("eventpoll: Fix + * semi-unbounded recursion") hardened the walk; any refactor must + * preserve both bail-outs. + */ +static DEFINE_MUTEX(epnested_mutex); +static u64 loop_check_gen = 0; + +#define PATH_ARR_SIZE 5 + +/* + * Per-do_epoll_ctl() scratch for the loop / path checks. Allocated on + * the caller's stack; populated by ep_ctl_lock() and the downward + * walk; consumed by reverse_path_check(); released by ep_ctl_unlock(). + * Only valid while the caller holds epnested_mutex. + */ +struct ep_ctl_ctx { + /* + * Outer eventpoll for one ep_loop_check(); if the downward walk + * reaches it the insert would form a cycle. + */ + struct eventpoll *inserting_into; + + /* + * Singly-linked list of epitems_head objects collected during + * ep_loop_check_proc(), then walked by reverse_path_check(). + * Terminated by EP_UNACTIVE_PTR, not NULL: epitems_head->next + * doubles as a membership flag (a NULL ->next means "not on this + * list", see ep_remove_file()), so the list uses a non-NULL + * sentinel to keep the tail head distinguishable from an unlisted + * one. + */ + struct epitems_head *tfile_check_list; + + /* + * Per-depth wakeup-path tally used by reverse_path_check_proc(); + * reinitialized to zero at the start of each reverse_path_check() + * iteration. + */ + int path_count[PATH_ARR_SIZE]; +}; + +/* Slab cache used to allocate "struct epitem" */ +static struct kmem_cache *epi_cache __ro_after_init; + +/* Slab cache used to allocate "struct eppoll_entry" */ +static struct kmem_cache *pwq_cache __ro_after_init; + +/* + * Wrapper anchor for file->f_ep when the watched file is not itself an + * eventpoll; for the epoll-watches-epoll case, file->f_ep points at + * &watched_ep->refs directly. The ->next field threads + * ctx->tfile_check_list during one EPOLL_CTL_ADD path check. The ->file + * field holds a reference to the associated file while the head is on + * the list. + */ +struct epitems_head { + struct hlist_head epitems; + struct epitems_head *next; + struct file *file; +}; + +static struct kmem_cache *ephead_cache __ro_after_init; + +static inline void free_ephead(struct epitems_head *head) +{ + if (head) + kmem_cache_free(ephead_cache, head); +} + +static void list_file(struct file *file, struct ep_ctl_ctx *ctx) +{ + struct epitems_head *head; + + head = container_of(file->f_ep, struct epitems_head, epitems); + if (!head->next) { + /* + * The caller owns a reference to @file or holds the ep->mtx for the + * epitem that led here. The latter blocks eventpoll_release_file() + * before the file allocation can be freed and reused. A dying leaf + * can be skipped since removing links cannot increase the reverse + * path count. + */ + if (!file_ref_get(&file->f_ref)) + return; + head->file = file; + head->next = ctx->tfile_check_list; + ctx->tfile_check_list = head; + } +} + +static void unlist_file(struct epitems_head *head) +{ + struct epitems_head *to_free = head; + struct hlist_node *p = rcu_dereference(hlist_first_rcu(&head->epitems)); + struct file *file = head->file; + if (p) { + struct epitem *epi= container_of(p, struct epitem, fllink); + spin_lock(&epi->ffd.file->f_lock); + if (!hlist_empty(&head->epitems)) + to_free = NULL; + head->next = NULL; + head->file = NULL; + spin_unlock(&epi->ffd.file->f_lock); + } + free_ephead(to_free); + fput(file); +} + +#ifdef CONFIG_SYSCTL + +#include <linux/sysctl.h> + +static long long_zero; +static long long_max = LONG_MAX; + +static const struct ctl_table epoll_table[] = { + { + .procname = "max_user_watches", + .data = &max_user_watches, + .maxlen = sizeof(max_user_watches), + .mode = 0644, + .proc_handler = proc_doulongvec_minmax, + .extra1 = &long_zero, + .extra2 = &long_max, + }, +}; + +static void __init epoll_sysctls_init(void) +{ + register_sysctl("fs/epoll", epoll_table); +} +#else +#define epoll_sysctls_init() do { } while (0) +#endif /* CONFIG_SYSCTL */ + +static const struct file_operations eventpoll_fops; + +bool is_file_epoll(struct file *f) +{ + return f->f_op == &eventpoll_fops; +} + +/* Compare RB tree keys */ +static inline int ep_cmp_ffd(struct epoll_key *p1, struct epoll_key *p2) +{ + return (p1->file > p2->file ? +1: + (p1->file < p2->file ? -1 : p1->fd - p2->fd)); +} + +/* True iff @epi is on its owning ep's ready list. */ +static inline bool ep_is_linked(struct epitem *epi) +{ + return !list_empty(&epi->rdllink); +} + +static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p) +{ + return container_of(p, struct eppoll_entry, wait); +} + +/* Get the "struct epitem" from a wait queue pointer */ +static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p) +{ + return container_of(p, struct eppoll_entry, wait)->base; +} + +/* + * Ready-list / ovflist state (see "Ready-list state machine" in the + * top-of-file banner for the full state machine). EP_UNACTIVE_PTR is + * the sentinel; these wrappers name each transition and each test so + * call sites do not need to know the sentinel's value. + */ + +/* True iff @ep is between ep_enter_scan() and ep_exit_scan(). */ +static inline bool ep_is_scanning(struct eventpoll *ep) +{ + return READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR; +} + +/* Called by ep_start_scan(): divert ep_poll_callback() to ovflist. */ +static inline void ep_enter_scan(struct eventpoll *ep) +{ + WRITE_ONCE(ep->ovflist, NULL); +} + +/* Called by ep_done_scan(): redirect ep_poll_callback() back to rdllist. */ +static inline void ep_exit_scan(struct eventpoll *ep) +{ + WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR); +} + +/* True iff @epi is currently linked on its ep's ovflist. */ +static inline bool epi_on_ovflist(const struct epitem *epi) +{ + return epi->ovflist_next != EP_UNACTIVE_PTR; +} + +/* Mark @epi as not on any ovflist (init and post-drain). */ +static inline void epi_clear_ovflist(struct epitem *epi) +{ + epi->ovflist_next = EP_UNACTIVE_PTR; +} + +/* True iff @ep has ready events that epoll_wait() might harvest. */ +static inline bool ep_events_available(struct eventpoll *ep) +{ + unsigned int seq = read_seqcount_begin(&ep->seq); + + return !list_empty_careful(&ep->rdllist) || ep_is_scanning(ep) || + read_seqcount_retry(&ep->seq, seq); +} + +#ifdef CONFIG_NET_RX_BUSY_POLL +/** + * busy_loop_ep_timeout - check if busy poll has timed out. The timeout value + * from the epoll instance ep is preferred, but if it is not set fallback to + * the system-wide global via busy_loop_timeout. + * + * @start_time: The start time used to compute the remaining time until timeout. + * @ep: Pointer to the eventpoll context. + * + * Return: true if the timeout has expired, false otherwise. + */ +static bool busy_loop_ep_timeout(unsigned long start_time, + struct eventpoll *ep) +{ + unsigned long bp_usec = READ_ONCE(ep->busy_poll_usecs); + + if (bp_usec) { + unsigned long end_time = start_time + bp_usec; + unsigned long now = busy_loop_current_time(); + + return time_after(now, end_time); + } else { + return busy_loop_timeout(start_time); + } +} + +static bool ep_busy_loop_on(struct eventpoll *ep) +{ + return !!READ_ONCE(ep->busy_poll_usecs) || + READ_ONCE(ep->prefer_busy_poll) || + net_busy_loop_on(); +} + +static bool ep_busy_loop_end(void *p, unsigned long start_time) +{ + struct eventpoll *ep = p; + + return ep_events_available(ep) || busy_loop_ep_timeout(start_time, ep); +} + +/* + * Busy poll if globally on and supporting sockets found && no events, + * busy loop will return if need_resched or ep_events_available. + * + * we must do our busy polling with irqs enabled + */ +static bool ep_busy_loop(struct eventpoll *ep) +{ + unsigned int napi_id = READ_ONCE(ep->napi_id); + u16 budget = READ_ONCE(ep->busy_poll_budget); + bool prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll); + + if (!budget) + budget = BUSY_POLL_BUDGET; + + if (napi_id_valid(napi_id) && ep_busy_loop_on(ep)) { + napi_busy_loop(napi_id, ep_busy_loop_end, + ep, prefer_busy_poll, budget); + if (ep_events_available(ep)) + return true; + /* + * Busy poll timed out. Drop NAPI ID for now, we can add + * it back in when we have moved a socket with a valid NAPI + * ID onto the ready list. + */ + if (prefer_busy_poll) + napi_resume_irqs(napi_id); + ep->napi_id = 0; + return false; + } + return false; +} + +/* + * Set epoll busy poll NAPI ID from sk. + */ +static inline void ep_set_busy_poll_napi_id(struct epitem *epi) +{ + struct eventpoll *ep = epi->ep; + unsigned int napi_id; + struct socket *sock; + struct sock *sk; + + if (!ep_busy_loop_on(ep)) + return; + + sock = sock_from_file(epi->ffd.file); + if (!sock) + return; + + sk = sock->sk; + if (!sk) + return; + + napi_id = READ_ONCE(sk->sk_napi_id); + + /* Non-NAPI IDs can be rejected + * or + * Nothing to do if we already have this ID + */ + if (!napi_id_valid(napi_id) || napi_id == ep->napi_id) + return; + + /* record NAPI ID for use in next busy poll */ + ep->napi_id = napi_id; +} + +static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd, + unsigned long arg) +{ + struct eventpoll *ep = file->private_data; + void __user *uarg = (void __user *)arg; + struct epoll_params epoll_params; + + switch (cmd) { + case EPIOCSPARAMS: + if (copy_from_user(&epoll_params, uarg, sizeof(epoll_params))) + return -EFAULT; + + /* pad byte must be zero */ + if (epoll_params.__pad) + return -EINVAL; + + if (epoll_params.busy_poll_usecs > S32_MAX) + return -EINVAL; + + if (epoll_params.prefer_busy_poll > 1) + return -EINVAL; + + if (epoll_params.busy_poll_budget > NAPI_POLL_WEIGHT && + !capable(CAP_NET_ADMIN)) + return -EPERM; + + WRITE_ONCE(ep->busy_poll_usecs, epoll_params.busy_poll_usecs); + WRITE_ONCE(ep->busy_poll_budget, epoll_params.busy_poll_budget); + WRITE_ONCE(ep->prefer_busy_poll, epoll_params.prefer_busy_poll); + return 0; + case EPIOCGPARAMS: + memset(&epoll_params, 0, sizeof(epoll_params)); + epoll_params.busy_poll_usecs = READ_ONCE(ep->busy_poll_usecs); + epoll_params.busy_poll_budget = READ_ONCE(ep->busy_poll_budget); + epoll_params.prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll); + if (copy_to_user(uarg, &epoll_params, sizeof(epoll_params))) + return -EFAULT; + return 0; + default: + return -ENOIOCTLCMD; + } +} + +static void ep_suspend_napi_irqs(struct eventpoll *ep) +{ + unsigned int napi_id = READ_ONCE(ep->napi_id); + + if (napi_id_valid(napi_id) && READ_ONCE(ep->prefer_busy_poll)) + napi_suspend_irqs(napi_id); +} + +static void ep_resume_napi_irqs(struct eventpoll *ep) +{ + unsigned int napi_id = READ_ONCE(ep->napi_id); + + if (napi_id_valid(napi_id) && READ_ONCE(ep->prefer_busy_poll)) + napi_resume_irqs(napi_id); +} + +#else + +static inline bool ep_busy_loop(struct eventpoll *ep) +{ + return false; +} + +static inline void ep_set_busy_poll_napi_id(struct epitem *epi) +{ +} + +static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd, + unsigned long arg) +{ + return -EOPNOTSUPP; +} + +static void ep_suspend_napi_irqs(struct eventpoll *ep) +{ +} + +static void ep_resume_napi_irqs(struct eventpoll *ep) +{ +} + +#endif /* CONFIG_NET_RX_BUSY_POLL */ + +/* + * As described in commit 0ccf831cb lockdep: annotate epoll + * the use of wait queues used by epoll is done in a very controlled + * manner. Wake ups can nest inside each other, but are never done + * with the same locking. For example: + * + * dfd = socket(...); + * efd1 = epoll_create(); + * efd2 = epoll_create(); + * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); + * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); + * + * When a packet arrives to the device underneath "dfd", the net code will + * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a + * callback wakeup entry on that queue, and the wake_up() performed by the + * "dfd" net code will end up in ep_poll_callback(). At this point epoll + * (efd1) notices that it may have some event ready, so it needs to wake up + * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() + * that ends up in another wake_up(), after having checked about the + * recursion constraints. That are, no more than EP_MAX_NESTS, to avoid + * stack blasting. + * + * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle + * this special case of epoll. + */ +#ifdef CONFIG_DEBUG_LOCK_ALLOC + +static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, + unsigned pollflags) +{ + struct eventpoll *ep_src; + unsigned long flags; + u8 nests = 0; + + /* + * To set the subclass or nesting level for spin_lock_irqsave_nested() + * it might be natural to create a per-cpu nest count. However, since + * we can recurse on ep->poll_wait.lock, and a non-raw spinlock can + * schedule() in the -rt kernel, the per-cpu variable are no longer + * protected. Thus, we are introducing a per eventpoll nest field. + * If we are not being call from ep_poll_callback(), epi is NULL and + * we are at the first level of nesting, 0. Otherwise, we are being + * called from ep_poll_callback() and if a previous wakeup source is + * not an epoll file itself, we are at depth 1 since the wakeup source + * is depth 0. If the wakeup source is a previous epoll file in the + * wakeup chain then we use its nests value and record ours as + * nests + 1. The previous epoll file nests value is stable since its + * already holding its own poll_wait.lock. + */ + if (epi) { + if ((is_file_epoll(epi->ffd.file))) { + ep_src = epi->ffd.file->private_data; + nests = ep_src->nests; + } else { + nests = 1; + } + } + spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests); + ep->nests = nests + 1; + wake_up_locked_poll(&ep->poll_wait, EPOLLIN | pollflags); + ep->nests = 0; + spin_unlock_irqrestore(&ep->poll_wait.lock, flags); +} + +#else + +static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, + __poll_t pollflags) +{ + wake_up_poll(&ep->poll_wait, EPOLLIN | pollflags); +} + +#endif + +static void ep_remove_wait_queue(struct eppoll_entry *pwq) +{ + wait_queue_head_t *whead; + + rcu_read_lock(); + /* + * POLLFREE handshake, acquire side; see "POLLFREE handshake" + * at the top of this file. + * + * A NULL load is paired with the smp_store_release(&whead, NULL) + * in ep_poll_callback()'s POLLFREE branch: the teardown is + * complete and we must not touch whead again. On a non-NULL load + * rcu_read_lock() keeps the waitqueue memory alive (POLLFREE + * firers RCU-defer the free) and whead->lock inside + * remove_wait_queue() serializes us against the store side. + */ + whead = smp_load_acquire(&pwq->whead); + if (whead) + remove_wait_queue(whead, &pwq->wait); + rcu_read_unlock(); +} + +/* + * This function unregisters poll callbacks from the associated file + * descriptor. Must be called with "mtx" held. + */ +static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) +{ + struct eppoll_entry **p = &epi->pwqlist; + struct eppoll_entry *pwq; + + while ((pwq = *p) != NULL) { + *p = pwq->next; + ep_remove_wait_queue(pwq); + kmem_cache_free(pwq_cache, pwq); + } +} + +/* call only when ep->mtx is held */ +static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi) +{ + return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx)); +} + +/* call only when ep->mtx is held */ +static inline void ep_pm_stay_awake(struct epitem *epi) +{ + struct wakeup_source *ws = ep_wakeup_source(epi); + + if (ws) + __pm_stay_awake(ws); +} + +static inline bool ep_has_wakeup_source(struct epitem *epi) +{ + return rcu_access_pointer(epi->ws) ? true : false; +} + +/* call when ep->mtx cannot be held (ep_poll_callback) */ +static inline void ep_pm_stay_awake_rcu(struct epitem *epi) +{ + struct wakeup_source *ws; + + rcu_read_lock(); + ws = rcu_dereference(epi->ws); + if (ws) + __pm_stay_awake(ws); + rcu_read_unlock(); +} + + +/* + * ep->mutex needs to be held because we could be hit by + * eventpoll_release_file() and epoll_ctl(). + */ +static void ep_start_scan(struct eventpoll *ep, struct list_head *scan_batch) +{ + /* + * Steal the ready list, and re-init the original one to the + * empty list. Also, set ep->ovflist to NULL so that events + * happening while looping w/out locks, are not lost. We cannot + * have the poll callback to queue directly on ep->rdllist, + * because we want the "sproc" callback to be able to do it + * in a lockless way. + */ + lockdep_assert_irqs_enabled(); + spin_lock_irq(&ep->lock); + write_seqcount_begin(&ep->seq); + + list_splice_init(&ep->rdllist, scan_batch); + ep_enter_scan(ep); + + write_seqcount_end(&ep->seq); + spin_unlock_irq(&ep->lock); +} + +static void ep_done_scan(struct eventpoll *ep, + struct list_head *scan_batch) +{ + struct epitem *epi, *nepi; + + spin_lock_irq(&ep->lock); + /* + * During the time we spent inside the "sproc" callback, some + * other events might have been queued by the poll callback. + * We re-insert them inside the main ready-list here. + */ + for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL; ) { + nepi = epi->ovflist_next; + epi_clear_ovflist(epi); + /* + * Skip items that the caller already returned via @scan_batch + * -- the list_splice() below takes care of those. + */ + if (!ep_is_linked(epi)) { + /* + * ovflist is LIFO; list_add() head-insert here + * reverses the iteration order into FIFO. + */ + list_add(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + } + } + + write_seqcount_begin(&ep->seq); + + /* Back out of scan mode; callbacks target ep->rdllist again. */ + ep_exit_scan(ep); + + /* + * Quickly re-inject items left on "scan_batch". + */ + list_splice(scan_batch, &ep->rdllist); + + write_seqcount_end(&ep->seq); + + __pm_relax(ep->ws); + + if (!list_empty(&ep->rdllist)) { + if (waitqueue_active(&ep->wq)) + wake_up(&ep->wq); + } + + spin_unlock_irq(&ep->lock); +} + +static void ep_get(struct eventpoll *ep) +{ + refcount_inc(&ep->refcount); +} + +/* + * Drop a reference to @ep; returns true iff it was the last, in which + * case the caller is responsible for ep_free(). + */ +static bool ep_put(struct eventpoll *ep) +{ + if (!refcount_dec_and_test(&ep->refcount)) + return false; + + WARN_ON_ONCE(!RB_EMPTY_ROOT(&ep->rbr.rb_root)); + return true; +} + +static void ep_free(struct eventpoll *ep) +{ + ep_resume_napi_irqs(ep); + mutex_destroy(&ep->mtx); + free_uid(ep->user); + wakeup_source_unregister(ep->ws); + /* ep_get_upwards_depth_proc() may still hold epi->ep under RCU */ + kfree_rcu(ep, rcu); +} + +/* + * Pin @epi->ffd.file for operations that require both safe dereference + * and exclusion from __fput(). + * + * struct file uses SLAB_TYPESAFE_BY_RCU, so a freed slot can be + * reassigned at any time. The bare load of epi->ffd.file is safe here + * because the caller holds ep->mtx and eventpoll_release_file() blocks + * on that mutex while tearing down the epi, so the backing file + * allocation cannot be freed and reused under us. An rcu_read_lock() + * is therefore unnecessary for the load. + * + * A successful file_ref_get() additionally blocks __fput() from + * starting on this file: once the refcount has reached zero it cannot + * come back. ep_remove() relies on that to touch file->f_lock and + * file->f_ep without racing eventpoll_release_file() (see commit + * a6dc643c6931). A NULL return means __fput() is already in flight; + * the caller must bail without touching the file, and + * eventpoll_release_file() will clean the epi up from its side. + */ +static struct file *epi_fget(const struct epitem *epi) +{ + struct file *file; + + file = epi->ffd.file; + if (!file_ref_get(&file->f_ref)) + file = NULL; + return file; +} + +/* + * Takes &file->f_lock; returns with it released. + */ +static void ep_remove_file(struct eventpoll *ep, struct epitem *epi, + struct file *file) +{ + struct epitems_head *to_free = NULL; + struct hlist_head *head; + + lockdep_assert_held(&ep->mtx); + + spin_lock(&file->f_lock); + head = file->f_ep; + if (hlist_is_singular_node(&epi->fllink, head)) { + /* + * Last watcher: publish NULL so the eventpoll_release() + * fastpath in include/linux/eventpoll.h can skip the slow + * path on a future __fput(). Safe because every f_ep writer + * either holds a pin on @file via epi_fget() or is __fput() + * itself -- see the comment in eventpoll_release(). + */ + WRITE_ONCE(file->f_ep, NULL); + if (!is_file_epoll(file)) { + struct epitems_head *v; + v = container_of(head, struct epitems_head, epitems); + if (!smp_load_acquire(&v->next)) + to_free = v; + } + } + hlist_del_rcu(&epi->fllink); + spin_unlock(&file->f_lock); + free_ephead(to_free); +} + +static void ep_remove_epi(struct eventpoll *ep, struct epitem *epi) +{ + lockdep_assert_held(&ep->mtx); + + rb_erase_cached(&epi->rbn, &ep->rbr); + + spin_lock_irq(&ep->lock); + if (ep_is_linked(epi)) + list_del_init(&epi->rdllink); + spin_unlock_irq(&ep->lock); + + wakeup_source_unregister(ep_wakeup_source(epi)); + /* + * At this point it is safe to free the eventpoll item. Use the union + * field epi->rcu, since we are trying to minimize the size of + * 'struct epitem'. The 'rbn' field is no longer in use. Protected by + * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make + * use of the rbn field. + */ + kfree_rcu(epi, rcu); + + percpu_counter_dec(&ep->user->epoll_watches); +} + +/* + * ep_remove variant for callers owing an additional reference to the ep + */ +static void ep_remove(struct eventpoll *ep, struct epitem *epi) +{ + struct file *file __free(fput) = NULL; + + lockdep_assert_irqs_enabled(); + lockdep_assert_held(&ep->mtx); + + ep_unregister_pollwait(ep, epi); + + /* + * If we manage to grab a reference it means we're not in + * eventpoll_release_file() and aren't going to be: once @file's + * refcount has reached zero, file_ref_get() cannot bring it back. + */ + file = epi_fget(epi); + if (!file) + return; + + ep_remove_file(ep, epi, file); + ep_remove_epi(ep, epi); + WARN_ON_ONCE(ep_put(ep)); +} + +/* + * Pass 1 of ep_clear_and_put(): drain every epi's pwqlist. + * ep_unregister_pollwait() takes each watched wait-queue head's lock, + * which synchronizes with any in-flight ep_poll_callback(); after + * this returns no callback can still be about to dereference an epi + * on this ep. Must strictly precede ep_drain_tree() -- fusing the + * two walks would let a callback queued on epi_i still fire after + * epi_{i+k} had already been freed. + */ +static void ep_drain_pollwaits(struct eventpoll *ep) +{ + struct rb_node *rbp; + struct epitem *epi; + + lockdep_assert_held(&ep->mtx); + + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + + ep_unregister_pollwait(ep, epi); + cond_resched(); + } +} + +/* + * Pass 2 of ep_clear_and_put(): ep_remove() every epi. The per-epi + * pwqlist is already empty (ep_drain_pollwaits ran), but the rest of + * ep_remove() still runs: epi_fget() pin, f_ep clear under f_lock, + * rbtree erase, rdllist unlink, kfree_rcu(epi). rb_next() is captured + * before each erase so the iteration is stable. + * + * A concurrent eventpoll_release_file() (removal path C) on a watched + * file serializes with us via ep->mtx; ep_remove() transparently + * hands off any epi whose file is in __fput() by bailing when + * epi_fget() returns NULL, and path C will clean that epi up. + */ +static void ep_drain_tree(struct eventpoll *ep) +{ + struct rb_node *rbp, *next; + struct epitem *epi; + + lockdep_assert_held(&ep->mtx); + + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = next) { + next = rb_next(rbp); + epi = rb_entry(rbp, struct epitem, rbn); + ep_remove(ep, epi); + cond_resched(); + } +} + +/* + * Removal path B (see "Removal paths" in the top-of-file banner): + * close of the epoll fd itself, reached via ep_eventpoll_release(). + * + * Two passes under ep->mtx: first ep_drain_pollwaits() quiesces + * in-flight callbacks, then ep_drain_tree() frees the epis. The + * ep->refcount is kept > 0 across the walk by the ep file's own + * share, which we drop below; ep_free() runs iff we were the last + * holder after the tree drained. + */ +static void ep_clear_and_put(struct eventpoll *ep) +{ + /* Release any threads blocked in poll-on-ep. */ + if (waitqueue_active(&ep->poll_wait)) + ep_poll_safewake(ep, NULL, 0); + + mutex_lock(&ep->mtx); + ep_drain_pollwaits(ep); + ep_drain_tree(ep); + mutex_unlock(&ep->mtx); + + if (ep_put(ep)) + ep_free(ep); +} + +static long ep_eventpoll_ioctl(struct file *file, unsigned int cmd, + unsigned long arg) +{ + int ret; + + if (!is_file_epoll(file)) + return -EINVAL; + + switch (cmd) { + case EPIOCSPARAMS: + case EPIOCGPARAMS: + ret = ep_eventpoll_bp_ioctl(file, cmd, arg); + break; + default: + ret = -EINVAL; + break; + } + + return ret; +} + +static int ep_eventpoll_release(struct inode *inode, struct file *file) +{ + struct eventpoll *ep = file->private_data; + + if (ep) + ep_clear_and_put(ep); + + return 0; +} + +static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth); + +static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int depth) +{ + struct eventpoll *ep = file->private_data; + LIST_HEAD(scan_batch); + struct epitem *epi, *tmp; + poll_table pt; + __poll_t res = 0; + + init_poll_funcptr(&pt, NULL); + + /* Insert inside our poll wait queue */ + poll_wait(file, &ep->poll_wait, wait); + + /* + * Proceed to find out if wanted events are really available inside + * the ready list. + */ + mutex_lock_nested(&ep->mtx, depth); + ep_start_scan(ep, &scan_batch); + list_for_each_entry_safe(epi, tmp, &scan_batch, rdllink) { + if (ep_item_poll(epi, &pt, depth + 1)) { + res = EPOLLIN | EPOLLRDNORM; + break; + } else { + /* + * Item has been dropped into the ready list by the poll + * callback, but it's not actually ready, as far as + * caller requested events goes. We can remove it here. + */ + __pm_relax(ep_wakeup_source(epi)); + list_del_init(&epi->rdllink); + } + } + ep_done_scan(ep, &scan_batch); + mutex_unlock(&ep->mtx); + return res; +} + +/* + * Differs from ep_eventpoll_poll() in that internal callers already have + * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested() + * is correctly annotated. + */ +static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, + int depth) +{ + struct file *file = epi_fget(epi); + __poll_t res; + + /* + * We could return EPOLLERR | EPOLLHUP or something, but let's + * treat this more as "file doesn't exist, poll didn't happen". + */ + if (!file) + return 0; + + pt->_key = epi->event.events; + if (!is_file_epoll(file)) + res = vfs_poll(file, pt); + else + res = __ep_eventpoll_poll(file, pt, depth); + fput(file); + return res & epi->event.events; +} + +static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait) +{ + return __ep_eventpoll_poll(file, wait, 0); +} + +#ifdef CONFIG_PROC_FS +static void ep_show_fdinfo(struct seq_file *m, struct file *f) +{ + struct eventpoll *ep = f->private_data; + struct rb_node *rbp; + + mutex_lock(&ep->mtx); + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + struct epitem *epi = rb_entry(rbp, struct epitem, rbn); + struct inode *inode = file_inode(epi->ffd.file); + + seq_printf(m, "tfd: %8d events: %8x data: %16llx " + " pos:%lli ino:%llx sdev:%x\n", + epi->ffd.fd, epi->event.events, + (long long)epi->event.data, + (long long)epi->ffd.file->f_pos, + inode->i_ino, inode->i_sb->s_dev); + if (seq_has_overflowed(m)) + break; + } + mutex_unlock(&ep->mtx); +} +#endif + +/* File callbacks that implement the eventpoll file behaviour */ +static const struct file_operations eventpoll_fops = { +#ifdef CONFIG_PROC_FS + .show_fdinfo = ep_show_fdinfo, +#endif + .release = ep_eventpoll_release, + .poll = ep_eventpoll_poll, + .llseek = noop_llseek, + .unlocked_ioctl = ep_eventpoll_ioctl, + .compat_ioctl = compat_ptr_ioctl, +}; + +/* + * This is called from eventpoll_release() to unlink files from the eventpoll + * interface. We need to have this facility to cleanup correctly files that are + * closed without being removed from the eventpoll interface. + */ +void eventpoll_release_file(struct file *file) +{ + struct eventpoll *ep; + struct epitem *epi; + + /* + * A concurrent ep_remove() cannot outrace us: it pins @file via + * epi_fget(), which fails once __fput() has dropped the refcount + * to zero -- the path we're on. So any racing ep_remove() bails + * and leaves the epi for us to clean up here. + */ +again: + spin_lock(&file->f_lock); + if (file->f_ep && file->f_ep->first) { + epi = hlist_entry(file->f_ep->first, struct epitem, fllink); + spin_unlock(&file->f_lock); + + /* + * ep access is safe as we still own a reference to the ep + * struct + */ + ep = epi->ep; + mutex_lock(&ep->mtx); + + ep_unregister_pollwait(ep, epi); + + ep_remove_file(ep, epi, file); + ep_remove_epi(ep, epi); + + mutex_unlock(&ep->mtx); + + if (ep_put(ep)) + ep_free(ep); + goto again; + } + spin_unlock(&file->f_lock); +} + +static int ep_alloc(struct eventpoll **pep) +{ + struct eventpoll *ep; + + ep = kzalloc_obj(*ep); + if (unlikely(!ep)) + return -ENOMEM; + + mutex_init(&ep->mtx); + spin_lock_init(&ep->lock); + seqcount_spinlock_init(&ep->seq, &ep->lock); + init_waitqueue_head(&ep->wq); + init_waitqueue_head(&ep->poll_wait); + INIT_LIST_HEAD(&ep->rdllist); + ep->rbr = RB_ROOT_CACHED; + ep->ovflist = EP_UNACTIVE_PTR; /* not scanning */ + ep->user = get_current_user(); + refcount_set(&ep->refcount, 1); + + *pep = ep; + + return 0; +} + +/* + * Search the file inside the eventpoll tree. The RB tree operations + * are protected by the "mtx" mutex, and ep_find() must be called with + * "mtx" held. + */ +static struct epitem *ep_find(struct eventpoll *ep, struct epoll_key *tf) +{ + int kcmp; + struct rb_node *rbp; + struct epitem *epi, *epir = NULL; + + for (rbp = ep->rbr.rb_root.rb_node; rbp; ) { + epi = rb_entry(rbp, struct epitem, rbn); + kcmp = ep_cmp_ffd(tf, &epi->ffd); + if (kcmp > 0) + rbp = rbp->rb_right; + else if (kcmp < 0) + rbp = rbp->rb_left; + else { + epir = epi; + break; + } + } + + return epir; +} + +/* + * This is the callback that is passed to the wait queue wakeup + * mechanism. It is called by the stored file descriptors when they + * have events to report. + */ +static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key) +{ + int pwake = 0; + struct epitem *epi = ep_item_from_wait(wait); + struct eventpoll *ep = epi->ep; + __poll_t pollflags = key_to_poll(key); + unsigned long flags; + int ewake = 0; + + spin_lock_irqsave(&ep->lock, flags); + + ep_set_busy_poll_napi_id(epi); + + /* + * If the event mask does not contain any poll(2) event, we consider the + * descriptor to be disabled. This condition is likely the effect of the + * EPOLLONESHOT bit that disables the descriptor when an event is received, + * until the next EPOLL_CTL_MOD will be issued. + */ + if (!(epi->event.events & ~EP_PRIVATE_BITS)) + goto out_unlock; + + /* + * Check the events coming with the callback. At this stage, not + * every device reports the events in the "key" parameter of the + * callback. We need to be able to handle both cases here, hence the + * test for "key" != NULL before the event match test. + */ + if (pollflags && !(pollflags & epi->event.events)) + goto out_unlock; + + /* + * If we are transferring events to userspace, we can hold no locks + * (because we're accessing user memory, and because of linux f_op->poll() + * semantics). All the events that happen during that period of time are + * chained in ep->ovflist and requeued later on. + */ + if (ep_is_scanning(ep)) { + if (!epi_on_ovflist(epi)) { + epi->ovflist_next = READ_ONCE(ep->ovflist); + WRITE_ONCE(ep->ovflist, epi); + ep_pm_stay_awake_rcu(epi); + } + } else if (!ep_is_linked(epi)) { + /* In the usual case, add event to ready list. */ + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake_rcu(epi); + } + + /* + * Wake up ( if active ) both the eventpoll wait list and the ->poll() + * wait list. + */ + if (waitqueue_active(&ep->wq)) { + if ((epi->event.events & EPOLLEXCLUSIVE) && + !(pollflags & POLLFREE)) { + switch (pollflags & EPOLLINOUT_BITS) { + case EPOLLIN: + if (epi->event.events & EPOLLIN) + ewake = 1; + break; + case EPOLLOUT: + if (epi->event.events & EPOLLOUT) + ewake = 1; + break; + case 0: + ewake = 1; + break; + } + } + if (sync) + wake_up_sync(&ep->wq); + else + wake_up(&ep->wq); + } + if (waitqueue_active(&ep->poll_wait)) + pwake++; + +out_unlock: + spin_unlock_irqrestore(&ep->lock, flags); + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(ep, epi, pollflags & EPOLL_URING_WAKE); + + if (!(epi->event.events & EPOLLEXCLUSIVE)) + ewake = 1; + + if (pollflags & POLLFREE) { + /* + * POLLFREE handshake, release side; see "POLLFREE handshake" + * at the top of this file. + * + * Unlink our wait entry with list_del_init rather than + * __remove_wait_queue: a concurrent ep_remove_wait_queue() + * that already loaded a non-NULL whead may still call + * remove_wait_queue() after us, and list_del_init() tolerates + * the second delete. + * + * smp_store_release(&whead, NULL) publishes the teardown to + * ep_remove_wait_queue()'s smp_load_acquire(). Before this + * store, a racing ep_clear_and_put() / ep_remove() reaches + * ep_remove_wait_queue() which sees whead != NULL and takes + * whead->lock -- the same lock held by our caller, so it + * serializes behind us. Once whead is zeroed, nothing else + * protects ep / epi / wait. + */ + list_del_init(&wait->entry); + smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL); + } + + return ewake; +} + +/* + * This is the callback that is used to add our wait queue to the + * target file wakeup lists. + */ +static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, + poll_table *pt) +{ + struct ep_pqueue *epq = container_of(pt, struct ep_pqueue, pt); + struct epitem *epi = epq->epi; + struct eppoll_entry *pwq; + + if (unlikely(!epi)) // an earlier allocation has failed + return; + + pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL); + if (unlikely(!pwq)) { + epq->epi = NULL; + return; + } + + init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); + pwq->whead = whead; + pwq->base = epi; + if (epi->event.events & EPOLLEXCLUSIVE) + add_wait_queue_exclusive(whead, &pwq->wait); + else + add_wait_queue(whead, &pwq->wait); + pwq->next = epi->pwqlist; + epi->pwqlist = pwq; +} + +static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi) +{ + int kcmp; + struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL; + struct epitem *epic; + bool leftmost = true; + + while (*p) { + parent = *p; + epic = rb_entry(parent, struct epitem, rbn); + kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); + if (kcmp > 0) { + p = &parent->rb_right; + leftmost = false; + } else + p = &parent->rb_left; + } + rb_link_node(&epi->rbn, parent, p); + rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost); +} + + + +/* + * Upper bound on wakeup paths emanating from any one watched file, + * indexed by path depth (1..PATH_ARR_SIZE). For example, we allow + * 1000 paths of length 1 from each watched file. These caps limit + * the wakeup amplification that can be built from epoll-watches- + * epoll topologies without rejecting reasonable usage. + * + * Enforced at EPOLL_CTL_ADD; CTL_MOD and CTL_DEL cannot add paths. + * The running tallies live in ctx->path_count[] and are protected by + * epnested_mutex. + */ +static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 }; + +static int path_count_inc(struct ep_ctl_ctx *ctx, int nests) +{ + /* Allow an arbitrary number of depth 1 paths */ + if (nests == 0) + return 0; + + if (++ctx->path_count[nests] > path_limits[nests]) + return -1; + return 0; +} + +static void path_count_init(struct ep_ctl_ctx *ctx) +{ + int i; + + for (i = 0; i < PATH_ARR_SIZE; i++) + ctx->path_count[i] = 0; +} + +static int reverse_path_check_proc(struct ep_ctl_ctx *ctx, + struct hlist_head *refs, int depth) +{ + int error = 0; + struct epitem *epi; + + if (depth > EP_MAX_NESTS) /* too deep nesting */ + return -1; + + /* CTL_DEL can remove links here, but that can't increase our count */ + hlist_for_each_entry_rcu(epi, refs, fllink) { + struct hlist_head *refs = &epi->ep->refs; + if (hlist_empty(refs)) + error = path_count_inc(ctx, depth); + else + error = reverse_path_check_proc(ctx, refs, depth + 1); + if (error != 0) + break; + } + return error; +} + +/** + * reverse_path_check - ctx->tfile_check_list is a list of epitems_head + * anchoring files with newly proposed links; make + * sure those links don't push any path-length bucket + * over its limit in path_limits[]. + * @ctx: Per-do_epoll_ctl() scratch for the loop / path checks. + * + * Return: %zero if the proposed links don't create too many paths, + * %-1 otherwise. + */ +static int reverse_path_check(struct ep_ctl_ctx *ctx) +{ + struct epitems_head *p; + + for (p = ctx->tfile_check_list; p != EP_UNACTIVE_PTR; p = p->next) { + int error; + path_count_init(ctx); + rcu_read_lock(); + error = reverse_path_check_proc(ctx, &p->epitems, 0); + rcu_read_unlock(); + if (error) + return error; + } + return 0; +} + +static int ep_create_wakeup_source(struct epitem *epi) +{ + struct name_snapshot n; + struct wakeup_source *ws; + + if (!epi->ep->ws) { + epi->ep->ws = wakeup_source_register(NULL, "eventpoll"); + if (!epi->ep->ws) + return -ENOMEM; + } + + take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry); + ws = wakeup_source_register(NULL, n.name.name); + release_dentry_name_snapshot(&n); + + if (!ws) + return -ENOMEM; + rcu_assign_pointer(epi->ws, ws); + + return 0; +} + +/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */ +static noinline void ep_destroy_wakeup_source(struct epitem *epi) +{ + struct wakeup_source *ws = ep_wakeup_source(epi); + + RCU_INIT_POINTER(epi->ws, NULL); + + /* + * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is + * used internally by wakeup_source_remove, too (called by + * wakeup_source_unregister), so we cannot use call_rcu + */ + synchronize_rcu(); + wakeup_source_unregister(ws); +} + +static int ep_attach_file(struct file *file, struct epitem *epi) +{ + struct epitems_head *to_free = NULL; + struct hlist_head *head = NULL; + struct eventpoll *ep = NULL; + + if (is_file_epoll(file)) + ep = file->private_data; + + if (ep) { + head = &ep->refs; + } else if (!READ_ONCE(file->f_ep)) { +allocate: + to_free = kmem_cache_zalloc(ephead_cache, GFP_KERNEL); + if (!to_free) + return -ENOMEM; + head = &to_free->epitems; + } + spin_lock(&file->f_lock); + if (!file->f_ep) { + if (unlikely(!head)) { + spin_unlock(&file->f_lock); + goto allocate; + } + /* See eventpoll_release() for details. */ + WRITE_ONCE(file->f_ep, head); + to_free = NULL; + } + hlist_add_head_rcu(&epi->fllink, file->f_ep); + spin_unlock(&file->f_lock); + free_ephead(to_free); + return 0; +} + +/* + * Charge the user's epoll_watches quota, allocate a fresh epitem for + * @tf, and initialize its fields. The returned item is not yet linked + * into any data structure; the caller must install it via + * ep_register_epitem() (which takes over on success) or kmem_cache_free() + * it and decrement epoll_watches on its own. + * + * Returns ERR_PTR(-ENOSPC) if the quota is exceeded, ERR_PTR(-ENOMEM) + * if the slab allocation fails. + */ +static struct epitem *ep_alloc_epitem(struct eventpoll *ep, + const struct epoll_event *event, + struct epoll_key *tf) +{ + struct epitem *epi; + + if (unlikely(percpu_counter_compare(&ep->user->epoll_watches, + max_user_watches) >= 0)) + return ERR_PTR(-ENOSPC); + percpu_counter_inc(&ep->user->epoll_watches); + + epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL); + if (unlikely(!epi)) { + percpu_counter_dec(&ep->user->epoll_watches); + return ERR_PTR(-ENOMEM); + } + + INIT_LIST_HEAD(&epi->rdllink); + epi->ep = ep; + epi->ffd = *tf; + epi->event = *event; + epi_clear_ovflist(epi); + + return epi; +} + +/* + * Install @epi into its target file's f_ep hlist and into @ep's rbtree, + * taking one additional reference on @ep for the lifetime of the item. + * + * If @tep is non-NULL, the target file is itself an eventpoll; we hold + * tep->mtx at subclass 1 across the attach + rbtree insert to serialize + * with the target side. RB tree ops are protected by @ep->mtx, which + * the caller already holds. + * + * On failure the epi is freed and the epoll_watches counter decremented, + * matching ep_alloc_epitem()'s allocation. After this returns + * successfully, ep_insert()'s later error paths use ep_remove() for + * unwind; that cannot drop @ep's refcount to zero because the ep file + * itself still holds the original reference. + */ +static int ep_register_epitem(struct ep_ctl_ctx *ctx, struct eventpoll *ep, + struct epitem *epi, struct eventpoll *tep, + int full_check) +{ + struct file *tfile = epi->ffd.file; + int error; + + if (tep) + mutex_lock_nested(&tep->mtx, 1); + + error = ep_attach_file(tfile, epi); + if (unlikely(error)) { + if (tep) + mutex_unlock(&tep->mtx); + kmem_cache_free(epi_cache, epi); + percpu_counter_dec(&ep->user->epoll_watches); + return error; + } + + if (full_check && !tep) + list_file(tfile, ctx); + + ep_rbtree_insert(ep, epi); + + if (tep) + mutex_unlock(&tep->mtx); + + ep_get(ep); + return 0; +} + +/* + * Must be called with "mtx" held. + */ +static int ep_insert(struct ep_ctl_ctx *ctx, struct eventpoll *ep, + const struct epoll_event *event, struct epoll_key *tf, + int full_check) +{ + int error, pwake = 0; + __poll_t revents; + struct epitem *epi; + struct ep_pqueue epq; + struct eventpoll *tep = NULL; + + if (is_file_epoll(tf->file)) + tep = tf->file->private_data; + + lockdep_assert_irqs_enabled(); + + epi = ep_alloc_epitem(ep, event, tf); + if (IS_ERR(epi)) + return PTR_ERR(epi); + + error = ep_register_epitem(ctx, ep, epi, tep, full_check); + if (error) + return error; + + /* Reject the insert if the new link would create too many back-paths. */ + if (unlikely(full_check && reverse_path_check(ctx))) { + ep_remove(ep, epi); + return -EINVAL; + } + + if (epi->event.events & EPOLLWAKEUP) { + error = ep_create_wakeup_source(epi); + if (error) { + ep_remove(ep, epi); + return error; + } + } + + /* Initialize the poll table using the queue callback */ + epq.epi = epi; + init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); + + /* + * Attach the item to the poll hooks and get current event bits. + * We can safely use the file* here because its usage count has + * been increased by the caller of this function. Note that after + * this operation completes, the poll callback can start hitting + * the new item. + */ + revents = ep_item_poll(epi, &epq.pt, 1); + + /* ep_ptable_queue_proc() signals allocation failure by clearing epq.epi. */ + if (unlikely(!epq.epi)) { + ep_remove(ep, epi); + return -ENOMEM; + } + + /* Drop the new item onto the ready list if it is already ready. */ + spin_lock_irq(&ep->lock); + + ep_set_busy_poll_napi_id(epi); + + if (revents && !ep_is_linked(epi)) { + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + + if (waitqueue_active(&ep->wq)) + wake_up(&ep->wq); + if (waitqueue_active(&ep->poll_wait)) + pwake++; + } + + spin_unlock_irq(&ep->lock); + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(ep, NULL, 0); + + return 0; +} + +/* + * Modify the interest event mask by dropping an event if the new mask + * has a match in the current file status. Must be called with "mtx" held. + */ +static int ep_modify(struct eventpoll *ep, struct epitem *epi, + const struct epoll_event *event) +{ + int pwake = 0; + poll_table pt; + + lockdep_assert_irqs_enabled(); + + init_poll_funcptr(&pt, NULL); + + /* + * Set the new event interest mask before calling f_op->poll(); + * otherwise we might miss an event that happens between the + * f_op->poll() call and the new event set registering. + */ + epi->event.events = event->events; /* need barrier below */ + epi->event.data = event->data; /* protected by mtx */ + if (epi->event.events & EPOLLWAKEUP) { + if (!ep_has_wakeup_source(epi)) + ep_create_wakeup_source(epi); + } else if (ep_has_wakeup_source(epi)) { + ep_destroy_wakeup_source(epi); + } + + /* + * The following barrier has two effects: + * + * 1) Flush epi changes above to other CPUs. This ensures + * we do not miss events from ep_poll_callback if an + * event occurs immediately after we call f_op->poll(). + * We need this because we did not take ep->lock while + * changing epi above (but ep_poll_callback does take + * ep->lock). + * + * 2) We also need to ensure we do not miss _past_ events + * when calling f_op->poll(). This barrier also + * pairs with the barrier in wq_has_sleeper (see + * comments for wq_has_sleeper). + * + * This barrier will now guarantee ep_poll_callback or f_op->poll + * (or both) will notice the readiness of an item. + */ + smp_mb(); + + /* + * Get current event bits. We can safely use the file* here because + * its usage count has been increased by the caller of this function. + * If the item is "hot" and it is not registered inside the ready + * list, push it inside. + */ + if (ep_item_poll(epi, &pt, 1)) { + spin_lock_irq(&ep->lock); + if (!ep_is_linked(epi)) { + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + + /* Notify waiting tasks that events are available */ + if (waitqueue_active(&ep->wq)) + wake_up(&ep->wq); + if (waitqueue_active(&ep->poll_wait)) + pwake++; + } + spin_unlock_irq(&ep->lock); + } + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(ep, NULL, 0); + + return 0; +} + +/* + * Attempt to deliver one event for @epi into @*uevents. + * + * Returns 1 if an event was delivered (with *uevents advanced to the + * next slot), 0 if the re-poll reported no caller-requested events + * (@epi drops out of the ready list; a future callback will re-add + * it), or -EFAULT if copy_to_user() faulted (in which case @epi is + * re-inserted at the head of @scan_batch so ep_done_scan() merges it + * back to rdllist for the next attempt). + * + * PM bookkeeping and level-triggered re-queue are handled here. + * Caller holds ep->mtx and the scan is active. + */ +static int ep_deliver_event(struct eventpoll *ep, struct epitem *epi, + poll_table *pt, + struct epoll_event __user **uevents, + struct list_head *scan_batch) +{ + struct epoll_event __user *next; + struct wakeup_source *ws; + __poll_t revents; + + /* + * Activate ep->ws before deactivating epi->ws to prevent + * triggering auto-suspend here (in case we reactivate epi->ws + * below). Rearranging to delay the deactivation would let + * epi->ws drift out of sync with ep_is_linked(). + */ + ws = ep_wakeup_source(epi); + if (ws) { + if (ws->active) + __pm_stay_awake(ep->ws); + __pm_relax(ws); + } + + list_del_init(&epi->rdllink); + + /* + * Re-poll under ep->mtx so userspace cannot change the item + * out from under us. If no caller-requested events remain, + * @epi stays off the ready list; the poll callback will + * re-queue it when events next appear. + */ + revents = ep_item_poll(epi, pt, 1); + if (!revents) + return 0; + + next = epoll_put_uevent(revents, epi->event.data, *uevents); + if (!next) { + /* + * copy_to_user() faulted: put the item back so + * ep_done_scan() splices it onto rdllist for the next + * attempt. + */ + list_add(&epi->rdllink, scan_batch); + ep_pm_stay_awake(epi); + return -EFAULT; + } + *uevents = next; + + if (epi->event.events & EPOLLONESHOT) { + epi->event.events &= EP_PRIVATE_BITS; + } else if (!(epi->event.events & EPOLLET)) { + /* + * Level-triggered: re-queue so the next epoll_wait() + * rechecks availability. We are the sole writer to + * rdllist here -- epoll_ctl() callers are locked out + * by ep->mtx, and the poll callback queues to ovflist + * during scans. + */ + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + } + return 1; +} + +static int ep_send_events(struct eventpoll *ep, + struct epoll_event __user *events, int maxevents) +{ + struct epitem *epi, *tmp; + LIST_HEAD(scan_batch); + poll_table pt; + int res = 0; + + /* + * Always short-circuit for fatal signals to allow threads to make a + * timely exit without the chance of finding more events available and + * fetching repeatedly. + */ + if (fatal_signal_pending(current)) + return -EINTR; + + init_poll_funcptr(&pt, NULL); + + mutex_lock(&ep->mtx); + ep_start_scan(ep, &scan_batch); + + /* + * We can loop without lock because we are passed a task-private + * scan_batch; items cannot vanish while we hold ep->mtx. + */ + list_for_each_entry_safe(epi, tmp, &scan_batch, rdllink) { + int delivered; + + if (res >= maxevents) + break; + + delivered = ep_deliver_event(ep, epi, &pt, &events, &scan_batch); + if (delivered < 0) { + if (!res) + res = delivered; + break; + } + res += delivered; + } + + ep_done_scan(ep, &scan_batch); + mutex_unlock(&ep->mtx); + + return res; +} + +static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms) +{ + struct timespec64 now; + + if (ms < 0) + return NULL; + + if (!ms) { + to->tv_sec = 0; + to->tv_nsec = 0; + return to; + } + + to->tv_sec = ms / MSEC_PER_SEC; + to->tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC); + + ktime_get_ts64(&now); + *to = timespec64_add_safe(now, *to); + return to; +} + +/* + * autoremove_wake_function, but remove even on failure to wake up, because we + * know that default_wake_function/ttwu will only fail if the thread is already + * woken, and in that case the ep_poll loop will remove the entry anyways, not + * try to reuse it. + */ +static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry, + unsigned int mode, int sync, void *key) +{ + int ret = default_wake_function(wq_entry, mode, sync, key); + + /* + * Pairs with list_empty_careful in ep_poll, and ensures future loop + * iterations see the cause of this wakeup. + */ + list_del_init_careful(&wq_entry->entry); + return ret; +} + +static int ep_try_send_events(struct eventpoll *ep, + struct epoll_event __user *events, int maxevents) +{ + int res; + + /* + * Try to transfer events to user space. In case we get 0 events and + * there's still timeout left over, we go trying again in search of + * more luck. + */ + res = ep_send_events(ep, events, maxevents); + if (res > 0) + ep_suspend_napi_irqs(ep); + return res; +} + +static int ep_schedule_timeout(ktime_t *to) +{ + if (to) + return ktime_after(*to, ktime_get()); + else + return 1; +} + +/** + * ep_poll - Retrieves ready events, and delivers them to the caller-supplied + * event buffer. + * + * @ep: Pointer to the eventpoll context. + * @events: Pointer to the userspace buffer where the ready events should be + * stored. + * @maxevents: Size (in terms of number of events) of the caller event buffer. + * @timeout: Maximum timeout for the ready events fetch operation, in + * timespec. If the timeout is zero, the function will not block, + * while if the @timeout ptr is NULL, the function will block + * until at least one event has been retrieved (or an error + * occurred). + * + * Return: the number of ready events which have been fetched, or an + * error code, in case of error. + */ +static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, + int maxevents, struct timespec64 *timeout) +{ + int res, timed_out = 0; + bool eavail; + u64 slack = 0; + wait_queue_entry_t wait; + ktime_t expires, *to = NULL; + + lockdep_assert_irqs_enabled(); + + if (timeout && (timeout->tv_sec | timeout->tv_nsec)) { + to = &expires; + *to = timespec64_to_ktime(*timeout); + } else if (timeout) { + /* + * Avoid the unnecessary trip to the wait queue loop, if the + * caller specified a non blocking operation. + */ + timed_out = 1; + } + + /* + * This call is racy: We may or may not see events that are being added + * to the ready list under the lock (e.g., in IRQ callbacks). For cases + * with a non-zero timeout, this thread will check the ready list under + * lock and will add to the wait queue. For cases with a zero + * timeout, the user by definition should not care and will have to + * recheck again. + */ + eavail = ep_events_available(ep); + + while (1) { + if (eavail) { + res = ep_try_send_events(ep, events, maxevents); + if (res) + return res; + } + + if (timed_out) + return 0; + + eavail = ep_busy_loop(ep); + if (eavail) + continue; + + if (signal_pending(current)) + return -EINTR; + + /* + * Internally init_wait() uses autoremove_wake_function(), + * thus wait entry is removed from the wait queue on each + * wakeup. Why it is important? In case of several waiters + * each new wakeup will hit the next waiter, giving it the + * chance to harvest new event. Otherwise wakeup can be + * lost. This is also good performance-wise, because on + * normal wakeup path no need to call __remove_wait_queue() + * explicitly, thus ep->lock is not taken, which halts the + * event delivery. + * + * In fact, we now use an even more aggressive function that + * unconditionally removes, because we don't reuse the wait + * entry between loop iterations. This lets us also avoid the + * performance issue if a process is killed, causing all of its + * threads to wake up without being removed normally. + */ + init_wait(&wait); + wait.func = ep_autoremove_wake_function; + + spin_lock_irq(&ep->lock); + /* + * Barrierless variant, waitqueue_active() is called under + * the same lock on wakeup ep_poll_callback() side, so it + * is safe to avoid an explicit barrier. + */ + __set_current_state(TASK_INTERRUPTIBLE); + + /* + * Do the final check under the lock. ep_start/done_scan() + * plays with two lists (->rdllist and ->ovflist) and there + * is always a race when both lists are empty for short + * period of time although events are pending, so lock is + * important. + */ + eavail = ep_events_available(ep); + if (!eavail) + __add_wait_queue_exclusive(&ep->wq, &wait); + + spin_unlock_irq(&ep->lock); + + if (!eavail) { + if (to) + slack = select_estimate_accuracy(timeout); + timed_out = !ep_schedule_timeout(to) || + !schedule_hrtimeout_range(to, slack, + HRTIMER_MODE_ABS); + } + __set_current_state(TASK_RUNNING); + + /* + * We were woken up, thus go and try to harvest some events. + * If timed out and still on the wait queue, recheck eavail + * carefully under lock, below. + */ + eavail = true; + + if (!list_empty_careful(&wait.entry)) { + spin_lock_irq(&ep->lock); + /* + * If the thread timed out and is not on the wait queue, + * it means that the thread was woken up after its + * timeout expired before it could reacquire the lock. + * Thus, when wait.entry is empty, it needs to harvest + * events. + */ + if (timed_out) + eavail = list_empty(&wait.entry); + __remove_wait_queue(&ep->wq, &wait); + spin_unlock_irq(&ep->lock); + } + } +} + +/** + * ep_loop_check_proc - verify that adding an epoll file @ep inside another + * epoll file does not create closed loops, and + * determine the depth of the subtree starting at @ep + * + * @ctx: Per-do_epoll_ctl() scratch for the loop / path checks. + * @ep: the &struct eventpoll to be currently checked. + * @depth: Current depth of the path being checked. + * + * Return: depth of the subtree, or a value bigger than EP_MAX_NESTS if we found + * a loop or went too deep. + */ +static int ep_loop_check_proc(struct ep_ctl_ctx *ctx, + struct eventpoll *ep, int depth) +{ + int result = 0; + struct rb_node *rbp; + struct epitem *epi; + + if (ep->gen == loop_check_gen) + return ep->loop_check_depth; + + mutex_lock_nested(&ep->mtx, depth + 1); + ep->gen = loop_check_gen; + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + if (unlikely(is_file_epoll(epi->ffd.file))) { + struct eventpoll *ep_tovisit; + ep_tovisit = epi->ffd.file->private_data; + if (ep_tovisit == ctx->inserting_into || + depth > EP_MAX_NESTS) + result = EP_MAX_NESTS+1; + else + result = max(result, + ep_loop_check_proc(ctx, ep_tovisit, + depth + 1) + 1); + if (result > EP_MAX_NESTS) + break; + } else { + /* + * A non-epoll leaf. Queue it for the companion + * reverse_path_check() that runs after this walk so + * any new links we propose don't add too many wakeup + * paths. + */ + list_file(epi->ffd.file, ctx); + } + } + ep->loop_check_depth = result; + mutex_unlock(&ep->mtx); + + return result; +} + +/* ep_get_upwards_depth_proc - determine depth of @ep when traversed upwards */ +static int ep_get_upwards_depth_proc(struct eventpoll *ep, int depth) +{ + int result = 0; + struct epitem *epi; + + if (ep->gen == loop_check_gen) + return ep->loop_check_depth; + hlist_for_each_entry_rcu(epi, &ep->refs, fllink) + result = max(result, ep_get_upwards_depth_proc(epi->ep, depth + 1) + 1); + ep->gen = loop_check_gen; + ep->loop_check_depth = result; + return result; +} + +/** + * ep_loop_check - Performs a check to verify that adding an epoll file (@to) + * into another epoll file (represented by @ep) does not create + * closed loops or too deep chains. + * + * @ctx: Per-CTL_ADD scratch context. + * @ep: Pointer to the epoll we are inserting into. + * @to: Pointer to the epoll to be inserted. + * + * Return: %zero if adding the epoll @to inside the epoll @from + * does not violate the constraints, or %-1 otherwise. + */ +static int ep_loop_check(struct ep_ctl_ctx *ctx, struct eventpoll *ep, + struct eventpoll *to) +{ + int depth, upwards_depth; + + ctx->inserting_into = ep; + /* + * Check how deep down we can get from @to, and whether it is possible + * to loop up to @ep. + */ + depth = ep_loop_check_proc(ctx, to, 0); + if (depth > EP_MAX_NESTS) + return -1; + /* Check how far up we can go from @ep. */ + rcu_read_lock(); + upwards_depth = ep_get_upwards_depth_proc(ep, 0); + rcu_read_unlock(); + + return (depth+1+upwards_depth > EP_MAX_NESTS) ? -1 : 0; +} + +static void clear_tfile_check_list(struct ep_ctl_ctx *ctx) +{ + rcu_read_lock(); + while (ctx->tfile_check_list != EP_UNACTIVE_PTR) { + struct epitems_head *head = ctx->tfile_check_list; + ctx->tfile_check_list = head->next; + unlist_file(head); + } + rcu_read_unlock(); +} + +/* + * Open an eventpoll file descriptor. + */ +static int do_epoll_create(int flags) +{ + int error; + struct eventpoll *ep; + + /* Check the EPOLL_* constant for consistency. */ + BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC); + + if (flags & ~EPOLL_CLOEXEC) + return -EINVAL; + /* + * Create the internal data structure ("struct eventpoll"). + */ + error = ep_alloc(&ep); + if (error < 0) + return error; + /* + * Creates all the items needed to setup an eventpoll file. That is, + * a file structure and a free file descriptor. + */ + FD_PREPARE(fdf, O_RDWR | (flags & O_CLOEXEC), + anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep, + O_RDWR | (flags & O_CLOEXEC))); + if (fdf.err) { + ep_clear_and_put(ep); + return fdf.err; + } + ep->file = fd_prepare_file(fdf); + return fd_publish(fdf); +} + +SYSCALL_DEFINE1(epoll_create1, int, flags) +{ + return do_epoll_create(flags); +} + +SYSCALL_DEFINE1(epoll_create, int, size) +{ + if (size <= 0) + return -EINVAL; + + return do_epoll_create(0); +} + +#ifdef CONFIG_PM_SLEEP +static inline void ep_take_care_of_epollwakeup(struct epoll_event *epev) +{ + if ((epev->events & EPOLLWAKEUP) && !capable(CAP_BLOCK_SUSPEND)) + epev->events &= ~EPOLLWAKEUP; +} +#else +static inline void ep_take_care_of_epollwakeup(struct epoll_event *epev) +{ + epev->events &= ~EPOLLWAKEUP; +} +#endif + +static inline int epoll_mutex_lock(struct mutex *mutex, bool nonblock) +{ + if (!nonblock) { + mutex_lock(mutex); + return 0; + } + return mutex_trylock(mutex) ? 0 : -EAGAIN; +} + +/* + * Acquire the locks required for do_epoll_ctl() on @ep for @op. + * + * Always takes ep->mtx. For EPOLL_CTL_ADD, additionally runs the + * loop / path check under epnested_mutex when the topology can + * change: @ep is already watched (epfile->f_ep non-NULL), @ep was + * recently loop-checked (ep->gen == loop_check_gen), or @tfile is + * itself an eventpoll. + * + * Return value encodes both outcome and lock state: + * + * 0 success; ep->mtx held. + * 1 success; ep->mtx held AND the full check ran under + * epnested_mutex (which is also still held). The value + * doubles as the @full_check argument to ep_insert(). + * -errno failure; no locks held. + * + * The caller releases what was taken with ep_ctl_unlock(ep, ret). + * + * Holding epnested_mutex on add is what prevents two racing + * EPOLL_CTL_ADDs on different eps from building a cycle without + * either walker observing it. + */ +static int ep_ctl_lock(struct ep_ctl_ctx *ctx, struct eventpoll *ep, int op, + struct file *epfile, struct file *tfile, bool nonblock) +{ + struct eventpoll *tep; + int error; + + error = epoll_mutex_lock(&ep->mtx, nonblock); + if (error) + return error; + + if (op != EPOLL_CTL_ADD) + return 0; + if (!READ_ONCE(epfile->f_ep) && ep->gen != loop_check_gen && + !is_file_epoll(tfile)) + return 0; + + /* Full check needed: drop ep->mtx so we can take epnested_mutex. */ + mutex_unlock(&ep->mtx); + error = epoll_mutex_lock(&epnested_mutex, nonblock); + if (error) + return error; + + loop_check_gen++; + + if (is_file_epoll(tfile)) { + tep = tfile->private_data; + if (ep_loop_check(ctx, ep, tep) != 0) { + error = -ELOOP; + goto err_unlock_nested; + } + } + + error = epoll_mutex_lock(&ep->mtx, nonblock); + if (error) + goto err_unlock_nested; + + return 1; + +err_unlock_nested: + clear_tfile_check_list(ctx); + loop_check_gen++; + mutex_unlock(&epnested_mutex); + return error; +} + +static void ep_ctl_unlock(struct ep_ctl_ctx *ctx, struct eventpoll *ep, + int full_check) +{ + mutex_unlock(&ep->mtx); + if (full_check) { + clear_tfile_check_list(ctx); + loop_check_gen++; + mutex_unlock(&epnested_mutex); + } +} + +int do_epoll_ctl_file(struct file *f, int op, struct epoll_key *tf, + struct epoll_event *epds, bool nonblock) +{ + int error; + int full_check; + struct eventpoll *ep; + struct epitem *epi; + struct ep_ctl_ctx ctx = { + .tfile_check_list = EP_UNACTIVE_PTR, + }; + + /* The target file descriptor must support poll */ + if (!file_can_poll(tf->file)) + return -EPERM; + + /* Check if EPOLLWAKEUP is allowed */ + if (ep_op_has_event(op)) + ep_take_care_of_epollwakeup(epds); + + /* + * The @f file must itself be an eventpoll, and we do not permit + * adding an epoll file descriptor inside itself. + */ + if (f == tf->file || !is_file_epoll(f)) + return -EINVAL; + + /* + * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only, + * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation. + * Also, nested exclusive wakeups are not supported. + */ + if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) { + if (op == EPOLL_CTL_MOD) + return -EINVAL; + if (op == EPOLL_CTL_ADD && (is_file_epoll(tf->file) || + (epds->events & ~EPOLLEXCLUSIVE_OK_BITS))) + return -EINVAL; + } + + ep = f->private_data; + + full_check = ep_ctl_lock(&ctx, ep, op, f, tf->file, nonblock); + if (full_check < 0) + return full_check; + + /* + * Look the target up in ep's RB tree. We hold ep->mtx, so the + * item stays valid until we release. + */ + epi = ep_find(ep, tf); + + error = -EINVAL; + switch (op) { + case EPOLL_CTL_ADD: + if (!epi) { + epds->events |= EPOLLERR | EPOLLHUP; + error = ep_insert(&ctx, ep, epds, tf, full_check); + } else + error = -EEXIST; + break; + case EPOLL_CTL_DEL: + if (epi) { + /* + * The eventpoll itself is still alive: the refcount + * can't go to zero here. + */ + ep_remove(ep, epi); + error = 0; + } else { + error = -ENOENT; + } + break; + case EPOLL_CTL_MOD: + if (epi) { + if (!(epi->event.events & EPOLLEXCLUSIVE)) { + epds->events |= EPOLLERR | EPOLLHUP; + error = ep_modify(ep, epi, epds); + } + } else + error = -ENOENT; + break; + } + + ep_ctl_unlock(&ctx, ep, full_check); + return error; +} + +int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, + bool nonblock) +{ + struct epoll_key efd; + + CLASS(fd, f)(epfd); + if (fd_empty(f)) + return -EBADF; + + /* Get the "struct file *" for the target file */ + CLASS(fd, tf)(fd); + if (fd_empty(tf)) + return -EBADF; + + efd.file = fd_file(tf); + efd.fd = fd; + return do_epoll_ctl_file(fd_file(f), op, &efd, epds, nonblock); +} + +/* + * The following function implements the controller interface for + * the eventpoll file that enables the insertion/removal/change of + * file descriptors inside the interest set. + */ +SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, + struct epoll_event __user *, event) +{ + struct epoll_event epds; + + if (ep_op_has_event(op) && + copy_from_user(&epds, event, sizeof(struct epoll_event))) + return -EFAULT; + + return do_epoll_ctl(epfd, op, fd, &epds, false); +} + +static int ep_check_params(struct file *file, struct epoll_event __user *evs, + int maxevents) +{ + /* The maximum number of event must be greater than zero */ + if (maxevents <= 0 || maxevents > EP_MAX_EVENTS) + return -EINVAL; + + /* Verify that the area passed by the user is writeable */ + if (!access_ok(evs, maxevents * sizeof(struct epoll_event))) + return -EFAULT; + + /* + * We have to check that the file structure underneath the fd + * the user passed to us _is_ an eventpoll file. + */ + if (!is_file_epoll(file)) + return -EINVAL; + + return 0; +} + +int epoll_sendevents(struct file *file, struct epoll_event __user *events, + int maxevents) +{ + struct eventpoll *ep; + int ret; + + ret = ep_check_params(file, events, maxevents); + if (unlikely(ret)) + return ret; + + ep = file->private_data; + /* + * Racy call, but that's ok - it should get retried based on + * poll readiness anyway. + */ + if (ep_events_available(ep)) + return ep_try_send_events(ep, events, maxevents); + return 0; +} + +/* + * Implement the event wait interface for the eventpoll file. It is the kernel + * part of the user space epoll_wait(2). + */ +static int do_epoll_wait(int epfd, struct epoll_event __user *events, + int maxevents, struct timespec64 *to) +{ + struct eventpoll *ep; + int ret; + + /* Get the "struct file *" for the eventpoll file */ + CLASS(fd, f)(epfd); + if (fd_empty(f)) + return -EBADF; + + ret = ep_check_params(fd_file(f), events, maxevents); + if (unlikely(ret)) + return ret; + + /* + * At this point it is safe to assume that the "private_data" contains + * our own data structure. + */ + ep = fd_file(f)->private_data; + + /* Time to fish for events ... */ + return ep_poll(ep, events, maxevents, to); +} + +SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, + int, maxevents, int, timeout) +{ + struct timespec64 to; + + return do_epoll_wait(epfd, events, maxevents, + ep_timeout_to_timespec(&to, timeout)); +} + +/* + * Implement the event wait interface for the eventpoll file. It is the kernel + * part of the user space epoll_pwait(2). + */ +static int do_epoll_pwait(int epfd, struct epoll_event __user *events, + int maxevents, struct timespec64 *to, + const sigset_t __user *sigmask, size_t sigsetsize) +{ + int error; + + /* + * If the caller wants a certain signal mask to be set during the wait, + * we apply it here. + */ + error = set_user_sigmask(sigmask, sigsetsize); + if (error) + return error; + + error = do_epoll_wait(epfd, events, maxevents, to); + + restore_saved_sigmask_unless(error == -EINTR); + + return error; +} + +SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events, + int, maxevents, int, timeout, const sigset_t __user *, sigmask, + size_t, sigsetsize) +{ + struct timespec64 to; + + return do_epoll_pwait(epfd, events, maxevents, + ep_timeout_to_timespec(&to, timeout), + sigmask, sigsetsize); +} + +SYSCALL_DEFINE6(epoll_pwait2, int, epfd, struct epoll_event __user *, events, + int, maxevents, const struct __kernel_timespec __user *, timeout, + const sigset_t __user *, sigmask, size_t, sigsetsize) +{ + struct timespec64 ts, *to = NULL; + + if (timeout) { + if (get_timespec64(&ts, timeout)) + return -EFAULT; + to = &ts; + if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) + return -EINVAL; + } + + return do_epoll_pwait(epfd, events, maxevents, to, + sigmask, sigsetsize); +} + +#ifdef CONFIG_KCMP +static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff) +{ + struct rb_node *rbp; + struct epitem *epi; + + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + if (epi->ffd.fd == tfd) { + if (toff == 0) + return epi; + else + toff--; + } + cond_resched(); + } + + return NULL; +} + +struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, + unsigned long toff) +{ + struct file *file_raw; + struct eventpoll *ep; + struct epitem *epi; + + if (!is_file_epoll(file)) + return ERR_PTR(-EINVAL); + + ep = file->private_data; + + mutex_lock(&ep->mtx); + epi = ep_find_tfd(ep, tfd, toff); + if (epi) + file_raw = epi->ffd.file; + else + file_raw = ERR_PTR(-ENOENT); + mutex_unlock(&ep->mtx); + + return file_raw; +} +#endif /* CONFIG_KCMP */ + +#ifdef CONFIG_COMPAT +static int do_compat_epoll_pwait(int epfd, struct epoll_event __user *events, + int maxevents, struct timespec64 *timeout, + const compat_sigset_t __user *sigmask, + compat_size_t sigsetsize) +{ + long err; + + /* + * If the caller wants a certain signal mask to be set during the wait, + * we apply it here. + */ + err = set_compat_user_sigmask(sigmask, sigsetsize); + if (err) + return err; + + err = do_epoll_wait(epfd, events, maxevents, timeout); + + restore_saved_sigmask_unless(err == -EINTR); + + return err; +} + +COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd, + struct epoll_event __user *, events, + int, maxevents, int, timeout, + const compat_sigset_t __user *, sigmask, + compat_size_t, sigsetsize) +{ + struct timespec64 to; + + return do_compat_epoll_pwait(epfd, events, maxevents, + ep_timeout_to_timespec(&to, timeout), + sigmask, sigsetsize); +} + +COMPAT_SYSCALL_DEFINE6(epoll_pwait2, int, epfd, + struct epoll_event __user *, events, + int, maxevents, + const struct __kernel_timespec __user *, timeout, + const compat_sigset_t __user *, sigmask, + compat_size_t, sigsetsize) +{ + struct timespec64 ts, *to = NULL; + + if (timeout) { + if (get_timespec64(&ts, timeout)) + return -EFAULT; + to = &ts; + if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) + return -EINVAL; + } + + return do_compat_epoll_pwait(epfd, events, maxevents, to, + sigmask, sigsetsize); +} + +#endif + +static int __init eventpoll_init(void) +{ + struct sysinfo si; + + si_meminfo(&si); + /* + * Allows top 4% of lomem to be allocated for epoll watches (per user). + */ + max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) / + EP_ITEM_COST; + BUG_ON(max_user_watches < 0); + + /* + * We can have many thousands of epitems, so prevent this from + * using an extra cache line on 64-bit (and smaller) CPUs + */ + BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128); + + /* Allocates slab cache used to allocate "struct epitem" items */ + epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), + 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL); + + /* Allocates slab cache used to allocate "struct eppoll_entry" */ + pwq_cache = kmem_cache_create("eventpoll_pwq", + sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); + epoll_sysctls_init(); + + ephead_cache = kmem_cache_create("ep_head", + sizeof(struct epitems_head), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); + + return 0; +} +fs_initcall(eventpoll_init); |