[PATCH 5.4 31/85] kthread_worker: prevent queuing delayed work from timer_fn when it is being canceled

[Greg Kroah-Hartman]

From: Zqiang <qiang.zh...@windriver.com>

commit 6993d0fdbee0eb38bfac350aa016f65ad11ed3b1 upstream.

There is a small race window when a delayed work is being canceled and
the work still might be queued from the timer_fn:

        CPU0                                            CPU1
kthread_cancel_delayed_work_sync()
   __kthread_cancel_work_sync()
     __kthread_cancel_work()
        work->canceling++;
                                              kthread_delayed_work_timer_fn()
                                                   kthread_insert_work();

BUG: kthread_insert_work() should not get called when work->canceling is
set.

Signed-off-by: Zqiang <qiang.zh...@windriver.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Reviewed-by: Petr Mladek <pmla...@suse.com>
Acked-by: Tejun Heo <t...@kernel.org>
Cc: <sta...@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201014083030.16895-1-qiang.zh...@windriver.com
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 kernel/kthread.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -873,7 +873,8 @@ void kthread_delayed_work_timer_fn(struc
        /* Move the work from worker->delayed_work_list. */
        WARN_ON_ONCE(list_empty(&work->node));
        list_del_init(&work->node);
-       kthread_insert_work(worker, work, &worker->work_list);
+       if (!work->canceling)
+               kthread_insert_work(worker, work, &worker->work_list);
 
        raw_spin_unlock_irqrestore(&worker->lock, flags);
 }