From: Jens Axboe <[email protected]>
To: Stefan Metzmacher <[email protected]>,
"Eric W. Biederman" <[email protected]>
Cc: Sasha Levin <[email protected]>,
[email protected], [email protected],
io-uring <[email protected]>,
Linus Torvalds <[email protected]>
Subject: Re: [PATCH AUTOSEL 5.11 43/44] signal: don't allow STOP on PF_IO_WORKER threads
Date: Thu, 25 Mar 2021 07:38:51 -0600 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 3/25/21 6:11 AM, Stefan Metzmacher wrote:
>
> Am 25.03.21 um 13:04 schrieb Eric W. Biederman:
>> Stefan Metzmacher <[email protected]> writes:
>>
>>> Am 25.03.21 um 12:24 schrieb Sasha Levin:
>>>> From: "Eric W. Biederman" <[email protected]>
>>>>
>>>> [ Upstream commit 4db4b1a0d1779dc159f7b87feb97030ec0b12597 ]
>>>>
>>>> Just like we don't allow normal signals to IO threads, don't deliver a
>>>> STOP to a task that has PF_IO_WORKER set. The IO threads don't take
>>>> signals in general, and have no means of flushing out a stop either.
>>>>
>>>> Longer term, we may want to look into allowing stop of these threads,
>>>> as it relates to eg process freezing. For now, this prevents a spin
>>>> issue if a SIGSTOP is delivered to the parent task.
>>>>
>>>> Reported-by: Stefan Metzmacher <[email protected]>
>>>> Signed-off-by: Jens Axboe <[email protected]>
>>>> Signed-off-by: "Eric W. Biederman" <[email protected]>
>>>> Signed-off-by: Sasha Levin <[email protected]>
>>>> ---
>>>> kernel/signal.c | 3 ++-
>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/kernel/signal.c b/kernel/signal.c
>>>> index 55526b941011..00a3840f6037 100644
>>>> --- a/kernel/signal.c
>>>> +++ b/kernel/signal.c
>>>> @@ -288,7 +288,8 @@ bool task_set_jobctl_pending(struct task_struct *task, unsigned long mask)
>>>> JOBCTL_STOP_SIGMASK | JOBCTL_TRAPPING));
>>>> BUG_ON((mask & JOBCTL_TRAPPING) && !(mask & JOBCTL_PENDING_MASK));
>>>>
>>>> - if (unlikely(fatal_signal_pending(task) || (task->flags & PF_EXITING)))
>>>> + if (unlikely(fatal_signal_pending(task) ||
>>>> + (task->flags & (PF_EXITING | PF_IO_WORKER))))
>>>> return false;
>>>>
>>>> if (mask & JOBCTL_STOP_SIGMASK)
>>>>
>>>
>>> Again, why is this proposed for 5.11 and 5.10 already?
>>
>> Has the bit about the io worker kthreads been backported?
>> If so this isn't horrible. If not this is nonsense.
No not yet - my plan is to do that, but not until we're 100% satisfied
with it.
> I don't know, I hope not...
>
> But I just tested v5.12-rc4 and attaching to
> an application with iothreads with gdb is still not possible,
> it still loops forever trying to attach to the iothreads.
I do see the looping, gdb apparently doesn't give up when it gets
-EPERM trying to attach to the threads. Which isn't really a kernel
thing, but:
> And I tested 'kill -9 $pidofiothread', and it feezed the whole
> machine...
that sounds very strange, I haven't seen anything like that running
the exact same scenario.
> So there's still work to do in order to get 5.12 stable.
>
> I'm short on time currently, but I hope to send more details soon.
Thanks! I'll play with it this morning and see if I can provoke
something odd related to STOP/attach.
--
Jens Axboe
next prev parent reply other threads:[~2021-03-25 13:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <[email protected]>
2021-03-25 11:24 ` [PATCH AUTOSEL 5.11 24/44] io_uring: fix ->flags races by linked timeouts Sasha Levin
2021-03-25 11:24 ` [PATCH AUTOSEL 5.11 25/44] io_uring: halt SQO submission on ctx exit Sasha Levin
2021-03-25 11:24 ` [PATCH AUTOSEL 5.11 37/44] io_uring: imply MSG_NOSIGNAL for send[msg]()/recv[msg]() calls Sasha Levin
2021-03-25 11:24 ` [PATCH AUTOSEL 5.11 44/44] io_uring: call req_set_fail_links() on short send[msg]()/recv[msg]() with MSG_WAITALL Sasha Levin
[not found] ` <[email protected]>
[not found] ` <[email protected]>
[not found] ` <[email protected]>
2021-03-25 12:11 ` [PATCH AUTOSEL 5.11 43/44] signal: don't allow STOP on PF_IO_WORKER threads Stefan Metzmacher
2021-03-25 13:38 ` Jens Axboe [this message]
2021-03-25 13:56 ` Stefan Metzmacher
2021-03-25 14:02 ` Jens Axboe
2021-03-25 15:00 ` Sasha Levin
2021-03-25 15:10 ` Jens Axboe
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