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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


  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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