The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 34b3d5344719d14fd2185b2d9459b3abcb8cf9d8 Mon Sep 17 00:00:00 2001 From: Petr Mladek <pmladek@xxxxxxxx> Date: Thu, 24 Jun 2021 18:39:45 -0700 Subject: [PATCH] kthread_worker: split code for canceling the delayed work timer Patch series "kthread_worker: Fix race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync()". This patchset fixes the race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync() including proper return value handling. This patch (of 2): Simple code refactoring as a preparation step for fixing a race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync(). It does not modify the existing behavior. Link: https://lkml.kernel.org/r/20210610133051.15337-2-pmladek@xxxxxxxx Signed-off-by: Petr Mladek <pmladek@xxxxxxxx> Cc: <jenhaochen@xxxxxxxxxx> Cc: Martin Liu <liumartin@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Nathan Chancellor <nathan@xxxxxxxxxx> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> diff --git a/kernel/kthread.c b/kernel/kthread.c index fe3f2a40d61e..121a0e1fc659 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1092,6 +1092,33 @@ void kthread_flush_work(struct kthread_work *work) } EXPORT_SYMBOL_GPL(kthread_flush_work); +/* + * Make sure that the timer is neither set nor running and could + * not manipulate the work list_head any longer. + * + * The function is called under worker->lock. The lock is temporary + * released but the timer can't be set again in the meantime. + */ +static void kthread_cancel_delayed_work_timer(struct kthread_work *work, + unsigned long *flags) +{ + struct kthread_delayed_work *dwork = + container_of(work, struct kthread_delayed_work, work); + struct kthread_worker *worker = work->worker; + + /* + * del_timer_sync() must be called to make sure that the timer + * callback is not running. The lock must be temporary released + * to avoid a deadlock with the callback. In the meantime, + * any queuing is blocked by setting the canceling counter. + */ + work->canceling++; + raw_spin_unlock_irqrestore(&worker->lock, *flags); + del_timer_sync(&dwork->timer); + raw_spin_lock_irqsave(&worker->lock, *flags); + work->canceling--; +} + /* * This function removes the work from the worker queue. Also it makes sure * that it won't get queued later via the delayed work's timer. @@ -1106,23 +1133,8 @@ static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork, unsigned long *flags) { /* Try to cancel the timer if exists. */ - if (is_dwork) { - struct kthread_delayed_work *dwork = - container_of(work, struct kthread_delayed_work, work); - struct kthread_worker *worker = work->worker; - - /* - * del_timer_sync() must be called to make sure that the timer - * callback is not running. The lock must be temporary released - * to avoid a deadlock with the callback. In the meantime, - * any queuing is blocked by setting the canceling counter. - */ - work->canceling++; - raw_spin_unlock_irqrestore(&worker->lock, *flags); - del_timer_sync(&dwork->timer); - raw_spin_lock_irqsave(&worker->lock, *flags); - work->canceling--; - } + if (is_dwork) + kthread_cancel_delayed_work_timer(work, flags); /* * Try to remove the work from a worker list. It might either
