From: "Jason A. Donenfeld" Jason@zx2c4.com
[ Upstream commit a7c01fa93aeb03ab76cd3cb2107990dd160498e6 ]
I was recently surprised to learn that msleep_interruptible(), wait_for_completion_interruptible_timeout(), and related functions simply hung when I called kthread_stop() on kthreads using them. The solution to fixing the case with msleep_interruptible() was more simply to move to schedule_timeout_interruptible(). Why?
The reason is that msleep_interruptible(), and many functions just like it, has a loop like this:
while (timeout && !signal_pending(current)) timeout = schedule_timeout_interruptible(timeout);
The call to kthread_stop() woke up the thread, so schedule_timeout_ interruptible() returned early, but because signal_pending() returned true, it went back into another timeout, which was never woken up.
This wait loop pattern is common to various pieces of code, and I suspect that the subtle misuse in a kthread that caused a deadlock in the code I looked at last week is also found elsewhere.
So this commit causes signal_pending() to return true when kthread_stop() is called, by setting TIF_NOTIFY_SIGNAL.
The same also probably applies to the similar kthread_park() functionality, but that can be addressed later, as its semantics are slightly different.
Cc: Eric W. Biederman ebiederm@xmission.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com v1: https://lkml.kernel.org/r/20220627120020.608117-1-Jason@zx2c4.com v2: https://lkml.kernel.org/r/20220627145716.641185-1-Jason@zx2c4.com v3: https://lkml.kernel.org/r/20220628161441.892925-1-Jason@zx2c4.com v4: https://lkml.kernel.org/r/20220711202136.64458-1-Jason@zx2c4.com v5: https://lkml.kernel.org/r/20220711232123.136330-1-Jason@zx2c4.com Signed-off-by: Eric W. Biederman ebiederm@xmission.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/kthread.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/kthread.c b/kernel/kthread.c index 3c677918d8f2..7243a010f433 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -704,6 +704,7 @@ int kthread_stop(struct task_struct *k) kthread = to_kthread(k); set_bit(KTHREAD_SHOULD_STOP, &kthread->flags); kthread_unpark(k); + set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL); wake_up_process(k); wait_for_completion(&kthread->exited); ret = kthread->result;