diff options
Diffstat (limited to 'mm/mmap_lock.c')
| -rw-r--r-- | mm/mmap_lock.c | 570 |
1 files changed, 570 insertions, 0 deletions
diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c new file mode 100644 index 000000000..898c2ef1e --- /dev/null +++ b/mm/mmap_lock.c @@ -0,0 +1,570 @@ +// SPDX-License-Identifier: GPL-2.0 +#define CREATE_TRACE_POINTS +#include <trace/events/mmap_lock.h> + +#include <linux/mm.h> +#include <linux/cgroup.h> +#include <linux/memcontrol.h> +#include <linux/mmap_lock.h> +#include <linux/mutex.h> +#include <linux/percpu.h> +#include <linux/rcupdate.h> +#include <linux/smp.h> +#include <linux/trace_events.h> +#include <linux/local_lock.h> + +EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking); +EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned); +EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released); + +#ifdef CONFIG_TRACING +/* + * Trace calls must be in a separate file, as otherwise there's a circular + * dependency between linux/mmap_lock.h and trace/events/mmap_lock.h. + */ + +void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write) +{ + trace_mmap_lock_start_locking(mm, write); +} +EXPORT_SYMBOL(__mmap_lock_do_trace_start_locking); + +void __mmap_lock_do_trace_acquire_returned(struct mm_struct *mm, bool write, + bool success) +{ + trace_mmap_lock_acquire_returned(mm, write, success); +} +EXPORT_SYMBOL(__mmap_lock_do_trace_acquire_returned); + +void __mmap_lock_do_trace_released(struct mm_struct *mm, bool write) +{ + trace_mmap_lock_released(mm, write); +} +EXPORT_SYMBOL(__mmap_lock_do_trace_released); +#endif /* CONFIG_TRACING */ + +#ifdef CONFIG_MMU +#ifdef CONFIG_PER_VMA_LOCK + +/* State shared across __vma_[start, end]_exclude_readers. */ +struct vma_exclude_readers_state { + /* Input parameters. */ + struct vm_area_struct *vma; + int state; /* TASK_KILLABLE or TASK_UNINTERRUPTIBLE. */ + bool detaching; + + /* Output parameters. */ + bool detached; + bool exclusive; /* Are we exclusively locked? */ +}; + +/* + * Now that all readers have been evicted, mark the VMA as being out of the + * 'exclude readers' state. + */ +static void __vma_end_exclude_readers(struct vma_exclude_readers_state *ves) +{ + struct vm_area_struct *vma = ves->vma; + + VM_WARN_ON_ONCE(ves->detached); + + ves->detached = refcount_sub_and_test(VM_REFCNT_EXCLUDE_READERS_FLAG, + &vma->vm_refcnt); + __vma_lockdep_release_exclusive(vma); +} + +static unsigned int get_target_refcnt(struct vma_exclude_readers_state *ves) +{ + const unsigned int tgt = ves->detaching ? 0 : 1; + + return tgt | VM_REFCNT_EXCLUDE_READERS_FLAG; +} + +/* + * Mark the VMA as being in a state of excluding readers, check to see if any + * VMA read locks are indeed held, and if so wait for them to be released. + * + * Note that this function pairs with vma_refcount_put() which will wake up this + * thread when it detects that the last reader has released its lock. + * + * The ves->state parameter ought to be set to TASK_UNINTERRUPTIBLE in cases + * where we wish the thread to sleep uninterruptibly or TASK_KILLABLE if a fatal + * signal is permitted to kill it. + * + * The function sets the ves->exclusive parameter to true if readers were + * excluded, or false if the VMA was detached or an error arose on wait. + * + * If the function indicates an exclusive lock was acquired via ves->exclusive + * the caller is required to invoke __vma_end_exclude_readers() once the + * exclusive state is no longer required. + * + * If ves->state is set to something other than TASK_UNINTERRUPTIBLE, the + * function may also return -EINTR to indicate a fatal signal was received while + * waiting. Otherwise, the function returns 0. + */ +static int __vma_start_exclude_readers(struct vma_exclude_readers_state *ves) +{ + struct vm_area_struct *vma = ves->vma; + unsigned int tgt_refcnt = get_target_refcnt(ves); + int err = 0; + + mmap_assert_write_locked(vma->vm_mm); + + /* + * If vma is detached then only vma_mark_attached() can raise the + * vm_refcnt. mmap_write_lock prevents racing with vma_mark_attached(). + * + * See the comment describing the vm_area_struct->vm_refcnt field for + * details of possible refcnt values. + */ + if (!refcount_add_not_zero(VM_REFCNT_EXCLUDE_READERS_FLAG, &vma->vm_refcnt)) { + ves->detached = true; + return 0; + } + + __vma_lockdep_acquire_exclusive(vma); + err = rcuwait_wait_event(&vma->vm_mm->vma_writer_wait, + refcount_read(&vma->vm_refcnt) == tgt_refcnt, + ves->state); + if (err) { + __vma_end_exclude_readers(ves); + return err; + } + + __vma_lockdep_stat_mark_acquired(vma); + ves->exclusive = true; + return 0; +} + +int __vma_start_write(struct vm_area_struct *vma, int state) +{ + const unsigned int mm_lock_seq = __vma_raw_mm_seqnum(vma); + struct vma_exclude_readers_state ves = { + .vma = vma, + .state = state, + }; + int err; + + err = __vma_start_exclude_readers(&ves); + if (err) { + WARN_ON_ONCE(ves.detached); + return err; + } + + /* + * We should use WRITE_ONCE() here because we can have concurrent reads + * from the early lockless pessimistic check in vma_start_read(). + * We don't really care about the correctness of that early check, but + * we should use WRITE_ONCE() for cleanliness and to keep KCSAN happy. + */ + WRITE_ONCE(vma->vm_lock_seq, mm_lock_seq); + + if (ves.exclusive) { + __vma_end_exclude_readers(&ves); + /* VMA should remain attached. */ + WARN_ON_ONCE(ves.detached); + } + + return 0; +} +EXPORT_SYMBOL_GPL(__vma_start_write); + +void __vma_exclude_readers_for_detach(struct vm_area_struct *vma) +{ + struct vma_exclude_readers_state ves = { + .vma = vma, + .state = TASK_UNINTERRUPTIBLE, + .detaching = true, + }; + int err; + + /* + * Wait until the VMA is detached with no readers. Since we hold the VMA + * write lock, the only read locks that might be present are those from + * threads trying to acquire the read lock and incrementing the + * reference count before realising the write lock is held and + * decrementing it. + */ + err = __vma_start_exclude_readers(&ves); + if (!err && ves.exclusive) { + /* + * Once this is complete, no readers can increment the + * reference count, and the VMA is marked detached. + */ + __vma_end_exclude_readers(&ves); + } + /* If an error arose but we were detached anyway, we don't care. */ + WARN_ON_ONCE(!ves.detached); +} + +/* + * Try to read-lock a vma. The function is allowed to occasionally yield false + * locked result to avoid performance overhead, in which case we fall back to + * using mmap_lock. The function should never yield false unlocked result. + * False locked result is possible if mm_lock_seq overflows or if vma gets + * reused and attached to a different mm before we lock it. + * Returns the vma on success, NULL on failure to lock and EAGAIN if vma got + * detached. + * + * IMPORTANT: RCU lock must be held upon entering the function, but upon error + * IT IS RELEASED. The caller must handle this correctly. + */ +static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm, + struct vm_area_struct *vma) +{ + struct mm_struct *other_mm; + int oldcnt; + + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "no rcu lock held"); + /* + * Check before locking. A race might cause false locked result. + * We can use READ_ONCE() for the mm_lock_seq here, and don't need + * ACQUIRE semantics, because this is just a lockless check whose result + * we don't rely on for anything - the mm_lock_seq read against which we + * need ordering is below. + */ + if (READ_ONCE(vma->vm_lock_seq) == READ_ONCE(mm->mm_lock_seq.sequence)) { + vma = NULL; + goto err; + } + + /* + * If VM_REFCNT_EXCLUDE_READERS_FLAG is set, + * __refcount_inc_not_zero_limited_acquire() will fail because + * VM_REFCNT_LIMIT is less than VM_REFCNT_EXCLUDE_READERS_FLAG. + * + * Acquire fence is required here to avoid reordering against later + * vm_lock_seq check and checks inside lock_vma_under_rcu(). + */ + if (unlikely(!__refcount_inc_not_zero_limited_acquire(&vma->vm_refcnt, &oldcnt, + VM_REFCNT_LIMIT))) { + /* return EAGAIN if vma got detached from under us */ + vma = oldcnt ? NULL : ERR_PTR(-EAGAIN); + goto err; + } + + __vma_lockdep_acquire_read(vma); + + if (unlikely(vma->vm_mm != mm)) + goto err_unstable; + + /* + * Overflow of vm_lock_seq/mm_lock_seq might produce false locked result. + * False unlocked result is impossible because we modify and check + * vma->vm_lock_seq under vma->vm_refcnt protection and mm->mm_lock_seq + * modification invalidates all existing locks. + * + * We must use ACQUIRE semantics for the mm_lock_seq so that if we are + * racing with vma_end_write_all(), we only start reading from the VMA + * after it has been unlocked. + * This pairs with RELEASE semantics in vma_end_write_all(). + */ + if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&mm->mm_lock_seq))) { + vma_refcount_put(vma); + vma = NULL; + goto err; + } + + return vma; +err: + rcu_read_unlock(); + + return vma; +err_unstable: + /* + * If vma got attached to another mm from under us, that mm is not + * stable and can be freed in the narrow window after vma->vm_refcnt + * is dropped and before rcuwait_wake_up(mm) is called. Grab it before + * releasing vma->vm_refcnt. + */ + other_mm = vma->vm_mm; /* use a copy as vma can be freed after we drop vm_refcnt */ + + /* __mmdrop() is a heavy operation, do it after dropping RCU lock. */ + rcu_read_unlock(); + mmgrab(other_mm); + vma_refcount_put(vma); + mmdrop(other_mm); + + return NULL; +} + +/* + * Lookup and lock a VMA under RCU protection. Returned VMA is guaranteed to be + * stable and not isolated. If the VMA is not found or is being modified the + * function returns NULL. + */ +struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, + unsigned long address) +{ + MA_STATE(mas, &mm->mm_mt, address, address); + struct vm_area_struct *vma; + +retry: + rcu_read_lock(); + vma = mas_walk(&mas); + if (!vma) { + rcu_read_unlock(); + goto inval; + } + + vma = vma_start_read(mm, vma); + if (IS_ERR_OR_NULL(vma)) { + /* Check if the VMA got isolated after we found it */ + if (PTR_ERR(vma) == -EAGAIN) { + count_vm_vma_lock_event(VMA_LOCK_MISS); + /* The area was replaced with another one */ + mas_set(&mas, address); + goto retry; + } + + /* Failed to lock the VMA */ + goto inval; + } + /* + * At this point, we have a stable reference to a VMA: The VMA is + * locked and we know it hasn't already been isolated. + * From here on, we can access the VMA without worrying about which + * fields are accessible for RCU readers. + */ + rcu_read_unlock(); + + /* Check if the vma we locked is the right one. */ + if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { + vma_end_read(vma); + goto inval; + } + + return vma; + +inval: + count_vm_vma_lock_event(VMA_LOCK_ABORT); + return NULL; +} + +static struct vm_area_struct *lock_next_vma_under_mmap_lock(struct mm_struct *mm, + struct vma_iterator *vmi, + unsigned long from_addr) +{ + struct vm_area_struct *vma; + int ret; + + ret = mmap_read_lock_killable(mm); + if (ret) + return ERR_PTR(ret); + + /* Lookup the vma at the last position again under mmap_read_lock */ + vma_iter_set(vmi, from_addr); + vma = vma_next(vmi); + if (vma) { + /* Very unlikely vma->vm_refcnt overflow case */ + if (unlikely(!vma_start_read_locked(vma))) + vma = ERR_PTR(-EAGAIN); + } + + mmap_read_unlock(mm); + + return vma; +} + +struct vm_area_struct *lock_next_vma(struct mm_struct *mm, + struct vma_iterator *vmi, + unsigned long from_addr) +{ + struct vm_area_struct *vma; + unsigned int mm_wr_seq; + bool mmap_unlocked; + + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "no rcu read lock held"); +retry: + /* Start mmap_lock speculation in case we need to verify the vma later */ + mmap_unlocked = mmap_lock_speculate_try_begin(mm, &mm_wr_seq); + vma = vma_next(vmi); + if (!vma) + return NULL; + + vma = vma_start_read(mm, vma); + if (IS_ERR_OR_NULL(vma)) { + /* + * Retry immediately if the vma gets detached from under us. + * Infinite loop should not happen because the vma we find will + * have to be constantly knocked out from under us. + */ + if (PTR_ERR(vma) == -EAGAIN) { + /* reset to search from the last address */ + rcu_read_lock(); + vma_iter_set(vmi, from_addr); + goto retry; + } + + goto fallback; + } + + /* Verify the vma is not behind the last search position. */ + if (unlikely(from_addr >= vma->vm_end)) + goto fallback_unlock; + + /* + * vma can be ahead of the last search position but we need to verify + * it was not shrunk after we found it and another vma has not been + * installed ahead of it. Otherwise we might observe a gap that should + * not be there. + */ + if (from_addr < vma->vm_start) { + /* Verify only if the address space might have changed since vma lookup. */ + if (!mmap_unlocked || mmap_lock_speculate_retry(mm, mm_wr_seq)) { + vma_iter_set(vmi, from_addr); + if (vma != vma_next(vmi)) + goto fallback_unlock; + } + } + + return vma; + +fallback_unlock: + rcu_read_unlock(); + vma_end_read(vma); +fallback: + vma = lock_next_vma_under_mmap_lock(mm, vmi, from_addr); + rcu_read_lock(); + /* Reinitialize the iterator after re-entering rcu read section */ + vma_iter_set(vmi, IS_ERR_OR_NULL(vma) ? from_addr : vma->vm_end); + + return vma; +} +#endif /* CONFIG_PER_VMA_LOCK */ + +#ifdef CONFIG_LOCK_MM_AND_FIND_VMA +#include <linux/extable.h> + +static inline bool get_mmap_lock_carefully(struct mm_struct *mm, struct pt_regs *regs) +{ + if (likely(mmap_read_trylock(mm))) + return true; + + if (regs && !user_mode(regs)) { + unsigned long ip = exception_ip(regs); + if (!search_exception_tables(ip)) + return false; + } + + return !mmap_read_lock_killable(mm); +} + +static inline bool mmap_upgrade_trylock(struct mm_struct *mm) +{ + /* + * We don't have this operation yet. + * + * It should be easy enough to do: it's basically a + * atomic_long_try_cmpxchg_acquire() + * from RWSEM_READER_BIAS -> RWSEM_WRITER_LOCKED, but + * it also needs the proper lockdep magic etc. + */ + return false; +} + +static inline bool upgrade_mmap_lock_carefully(struct mm_struct *mm, struct pt_regs *regs) +{ + mmap_read_unlock(mm); + if (regs && !user_mode(regs)) { + unsigned long ip = exception_ip(regs); + if (!search_exception_tables(ip)) + return false; + } + return !mmap_write_lock_killable(mm); +} + +/* + * Helper for page fault handling. + * + * This is kind of equivalent to "mmap_read_lock()" followed + * by "find_extend_vma()", except it's a lot more careful about + * the locking (and will drop the lock on failure). + * + * For example, if we have a kernel bug that causes a page + * fault, we don't want to just use mmap_read_lock() to get + * the mm lock, because that would deadlock if the bug were + * to happen while we're holding the mm lock for writing. + * + * So this checks the exception tables on kernel faults in + * order to only do this all for instructions that are actually + * expected to fault. + * + * We can also actually take the mm lock for writing if we + * need to extend the vma, which helps the VM layer a lot. + */ +struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm, + unsigned long addr, struct pt_regs *regs) +{ + struct vm_area_struct *vma; + + if (!get_mmap_lock_carefully(mm, regs)) + return NULL; + + vma = find_vma(mm, addr); + if (likely(vma && (vma->vm_start <= addr))) + return vma; + + /* + * Well, dang. We might still be successful, but only + * if we can extend a vma to do so. + */ + if (!vma || !(vma->vm_flags & VM_GROWSDOWN)) { + mmap_read_unlock(mm); + return NULL; + } + + /* + * We can try to upgrade the mmap lock atomically, + * in which case we can continue to use the vma + * we already looked up. + * + * Otherwise we'll have to drop the mmap lock and + * re-take it, and also look up the vma again, + * re-checking it. + */ + if (!mmap_upgrade_trylock(mm)) { + if (!upgrade_mmap_lock_carefully(mm, regs)) + return NULL; + + vma = find_vma(mm, addr); + if (!vma) + goto fail; + if (vma->vm_start <= addr) + goto success; + if (!(vma->vm_flags & VM_GROWSDOWN)) + goto fail; + } + + if (expand_stack_locked(vma, addr)) + goto fail; + +success: + mmap_write_downgrade(mm); + return vma; + +fail: + mmap_write_unlock(mm); + return NULL; +} +#endif /* CONFIG_LOCK_MM_AND_FIND_VMA */ + +#else /* CONFIG_MMU */ + +/* + * At least xtensa ends up having protection faults even with no + * MMU.. No stack expansion, at least. + */ +struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm, + unsigned long addr, struct pt_regs *regs) +{ + struct vm_area_struct *vma; + + mmap_read_lock(mm); + vma = vma_lookup(mm, addr); + if (!vma) + mmap_read_unlock(mm); + return vma; +} + +#endif /* CONFIG_MMU */ |