linux-kernel - Re: [PATCH AUTOSEL 5.11 43/44] signal: don't allow STOP on PF_IO

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Message-ID: <m1r1k34ey1.fsf@fess.ebiederm.org>
Date:   Thu, 25 Mar 2021 07:04:38 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Stefan Metzmacher <metze@...ba.org>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH AUTOSEL 5.11 43/44] signal: don't allow STOP on PF_IO_WORKER threads

Stefan Metzmacher <metze@...ba.org> writes:

> Am 25.03.21 um 12:24 schrieb Sasha Levin:
>> From: "Eric W. Biederman" <ebiederm@...ssion.com>
>> 
>> [ 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 <metze@...ba.org>
>> Signed-off-by: Jens Axboe <axboe@...nel.dk>
>> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>> Signed-off-by: Sasha Levin <sashal@...nel.org>
>> ---
>>  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.

Eric