The patch below does not apply to the 4.9-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@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 34b3d5344719d14fd2185b2d9459b3abcb8cf9d8 Mon Sep 17 00:00:00 2001

From: Petr Mladek pmladek@suse.com 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@suse.com Signed-off-by: Petr Mladek pmladek@suse.com Cc: jenhaochen@google.com Cc: Martin Liu liumartin@google.com Cc: Minchan Kim minchan@google.com Cc: Nathan Chancellor nathan@kernel.org Cc: Nick Desaulniers ndesaulniers@google.com Cc: Oleg Nesterov oleg@redhat.com Cc: Tejun Heo tj@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org

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