From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- fs/proc/namespaces.c | 196 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 196 insertions(+) create mode 100644 fs/proc/namespaces.c (limited to 'fs/proc/namespaces.c') diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c new file mode 100644 index 000000000..ea6ec61a0 --- /dev/null +++ b/fs/proc/namespaces.c @@ -0,0 +1,196 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include "internal.h" + + +static const struct proc_ns_operations *const ns_entries[] = { +#ifdef CONFIG_NET_NS + &netns_operations, +#endif +#ifdef CONFIG_UTS_NS + &utsns_operations, +#endif +#ifdef CONFIG_IPC_NS + &ipcns_operations, +#endif +#ifdef CONFIG_PID_NS + &pidns_operations, + &pidns_for_children_operations, +#endif +#ifdef CONFIG_USER_NS + &userns_operations, +#endif + &mntns_operations, +#ifdef CONFIG_CGROUPS + &cgroupns_operations, +#endif +#ifdef CONFIG_TIME_NS + &timens_operations, + &timens_for_children_operations, +#endif +}; + +static const char *proc_ns_get_link(struct dentry *dentry, + struct inode *inode, + struct delayed_call *done) +{ + const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops; + struct task_struct *task; + struct path ns_path; + int error; + + if (!dentry) + return ERR_PTR(-ECHILD); + + task = get_proc_task(inode); + if (!task) + return ERR_PTR(-EACCES); + + error = down_read_killable(&task->signal->exec_update_lock); + if (error) + goto out_put_task; + + error = -EACCES; + if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) + goto out; + + error = ns_get_path(&ns_path, task, ns_ops); + if (error) + goto out; + + error = nd_jump_link(&ns_path); +out: + up_read(&task->signal->exec_update_lock); +out_put_task: + put_task_struct(task); + return ERR_PTR(error); +} + +static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int buflen) +{ + struct inode *inode = d_inode(dentry); + const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops; + struct task_struct *task; + char name[50]; + int res = -EACCES; + + task = get_proc_task(inode); + if (!task) + return res; + + res = down_read_killable(&task->signal->exec_update_lock); + if (res) + goto out_put_task; + + res = -EACCES; + if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) { + res = ns_get_name(name, sizeof(name), task, ns_ops); + if (res >= 0) + res = readlink_copy(buffer, buflen, name, strlen(name)); + } + up_read(&task->signal->exec_update_lock); +out_put_task: + put_task_struct(task); + return res; +} + +static const struct inode_operations proc_ns_link_inode_operations = { + .readlink = proc_ns_readlink, + .get_link = proc_ns_get_link, + .setattr = proc_nochmod_setattr, +}; + +static struct dentry *proc_ns_instantiate(struct dentry *dentry, + struct task_struct *task, const void *ptr) +{ + const struct proc_ns_operations *ns_ops = ptr; + struct inode *inode; + struct proc_inode *ei; + + inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK | S_IRWXUGO); + if (!inode) + return ERR_PTR(-ENOENT); + + ei = PROC_I(inode); + inode->i_op = &proc_ns_link_inode_operations; + ei->ns_ops = ns_ops; + pid_update_inode(task, inode); + + return d_splice_alias_ops(inode, dentry, &pid_dentry_operations); +} + +static int proc_ns_dir_readdir(struct file *file, struct dir_context *ctx) +{ + struct task_struct *task = get_proc_task(file_inode(file)); + const struct proc_ns_operations *const *entry, *const *last; + + if (!task) + return -ENOENT; + + if (!dir_emit_dots(file, ctx)) + goto out; + if (ctx->pos >= 2 + ARRAY_SIZE(ns_entries)) + goto out; + entry = ns_entries + (ctx->pos - 2); + last = &ns_entries[ARRAY_SIZE(ns_entries) - 1]; + while (entry <= last) { + const struct proc_ns_operations *ops = *entry; + if (!proc_fill_cache(file, ctx, ops->name, strlen(ops->name), + proc_ns_instantiate, task, ops)) + break; + ctx->pos++; + entry++; + } +out: + put_task_struct(task); + return 0; +} + +const struct file_operations proc_ns_dir_operations = { + .read = generic_read_dir, + .iterate_shared = proc_ns_dir_readdir, + .llseek = generic_file_llseek, +}; + +static struct dentry *proc_ns_dir_lookup(struct inode *dir, + struct dentry *dentry, unsigned int flags) +{ + struct task_struct *task = get_proc_task(dir); + const struct proc_ns_operations *const *entry, *const *last; + unsigned int len = dentry->d_name.len; + struct dentry *res = ERR_PTR(-ENOENT); + + if (!task) + goto out_no_task; + + last = &ns_entries[ARRAY_SIZE(ns_entries)]; + for (entry = ns_entries; entry < last; entry++) { + if (strlen((*entry)->name) != len) + continue; + if (!memcmp(dentry->d_name.name, (*entry)->name, len)) + break; + } + if (entry == last) + goto out; + + res = proc_ns_instantiate(dentry, task, *entry); +out: + put_task_struct(task); +out_no_task: + return res; +} + +const struct inode_operations proc_ns_dir_inode_operations = { + .lookup = proc_ns_dir_lookup, + .getattr = pid_getattr, + .setattr = proc_nochmod_setattr, +}; -- cgit v1.3.1