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* [PATCH AUTOSEL 5.19 01/10] signal: break out of wait loops on kthread_stop()
@ 2022-10-14 13:52 Sasha Levin
  2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 02/10] powerpc/selftests: Use timersub() for gettimeofday() Sasha Levin
                   ` (8 more replies)
  0 siblings, 9 replies; 11+ messages in thread
From: Sasha Levin @ 2022-10-14 13:52 UTC (permalink / raw)
  To: linux-kernel, stable
  Cc: Jason A. Donenfeld, Eric W . Biederman, Sasha Levin, akpm,
	pmladek, laoar.shao, dinguyen, cai.huoqing, arnd

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;
-- 
2.35.1


^ permalink raw reply related	[flat|nested] 11+ messages in thread

end of thread, other threads:[~2022-11-02 18:02 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2022-10-14 13:52 [PATCH AUTOSEL 5.19 01/10] signal: break out of wait loops on kthread_stop() Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 02/10] powerpc/selftests: Use timersub() for gettimeofday() Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 03/10] kvm: x86: Do proper cleanup if kvm_x86_ops->vm_init() fails Sasha Levin
2022-11-02 18:01   ` Paolo Bonzini
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 04/10] powerpc/math-emu: Remove -w build flag and fix warnings Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 05/10] powerpc/85xx: Fix fall-through warning for Clang Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 06/10] powerpc: Remove direct call to personality syscall handler Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 07/10] powerpc/perf: Fix branch_filter support for multiple filters Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 08/10] powerpc/rtas: block error injection when locked down Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 09/10] powerpc/mm: Fix UBSAN warning reported on hugetlb Sasha Levin
2022-10-14 13:52 ` [PATCH AUTOSEL 5.19 10/10] powerpc/64: Fix msr_check_and_set/clear MSR[EE] race Sasha Levin

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