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authorJason A. Donenfeld <Jason@zx2c4.com>2022-06-27 13:40:47 +0200
committerJason A. Donenfeld <Jason@zx2c4.com>2022-06-29 15:17:38 +0200
commit0f215784215ac56485e749be49b3f261150942ed (patch)
treeb7104e594d10b087a4f0d46d36fd9893694a01ff
parentdt-bindings: chosen: remove (diff)
downloadlinux-dev-0f215784215ac56485e749be49b3f261150942ed.tar.xz
linux-dev-0f215784215ac56485e749be49b3f261150942ed.zip
signal: break out of wait loops on kthread_stop()
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 applies to the similar kthread_park() functionality. Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Toke Høiland-Jørgensen <toke@redhat.com> Cc: Kalle Valo <kvalo@kernel.org> Cc: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
-rw-r--r--kernel/kthread.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 3c677918d8f2..63d5a1f4cb93 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -661,12 +661,14 @@ int kthread_park(struct task_struct *k)
set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
if (k != current) {
+ test_and_set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
wake_up_process(k);
/*
* Wait for __kthread_parkme() to complete(), this means we
* _will_ have TASK_PARKED and are about to call schedule().
*/
wait_for_completion(&kthread->parked);
+ clear_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
/*
* Now wait for that schedule() to complete and the task to
* get scheduled out.
@@ -704,8 +706,10 @@ int kthread_stop(struct task_struct *k)
kthread = to_kthread(k);
set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
kthread_unpark(k);
+ test_and_set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
wake_up_process(k);
wait_for_completion(&kthread->exited);
+ clear_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
ret = kthread->result;
put_task_struct(k);