linux-kernel - Re: [PATCH 2/8] kernel: unmask SIGSTOP for IO threads

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Message-ID: <8f2a4b48-77c9-393f-5194-100ed63c05fc@samba.org>
Date:   Fri, 26 Mar 2021 16:23:34 +0100
From:   Stefan Metzmacher <metze@...ba.org>
To:     Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>
Cc:     io-uring@...r.kernel.org, torvalds@...ux-foundation.org,
        ebiederm@...ssion.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] kernel: unmask SIGSTOP for IO threads

Am 26.03.21 um 16:01 schrieb Jens Axboe:
> On 3/26/21 7:48 AM, Oleg Nesterov wrote:
>> Jens, sorry, I got lost :/
> 
> Let's bring you back in :-)
> 
>> On 03/25, Jens Axboe wrote:
>>>
>>> With IO threads accepting signals, including SIGSTOP,
>>
>> where can I find this change? Looks like I wasn't cc'ed...
> 
> It's this very series.
> 
>>> unmask the
>>> SIGSTOP signal from the default blocked mask.
>>>
>>> Signed-off-by: Jens Axboe <axboe@...nel.dk>
>>> ---
>>>  kernel/fork.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/fork.c b/kernel/fork.c
>>> index d3171e8e88e5..d5a40552910f 100644
>>> --- a/kernel/fork.c
>>> +++ b/kernel/fork.c
>>> @@ -2435,7 +2435,7 @@ struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node)
>>>  	tsk = copy_process(NULL, 0, node, &args);
>>>  	if (!IS_ERR(tsk)) {
>>>  		sigfillset(&tsk->blocked);
>>> -		sigdelsetmask(&tsk->blocked, sigmask(SIGKILL));
>>> +		sigdelsetmask(&tsk->blocked, sigmask(SIGKILL)|sigmask(SIGSTOP));
>>
>> siginitsetinv(blocked, sigmask(SIGKILL)|sigmask(SIGSTOP)) but this is minor.
> 
> Ah thanks.
> 
>> To remind, either way this is racy and can't really help.
>>
>> And if "IO threads accepting signals" then I don't understand why. Sorry,
>> I must have missed something.
> 
> I do think the above is a no-op at this point, and we can probably just
> kill it. Let me double check, hopefully we can just remove this blocked
> part.

Is this really correct to drop in your "kernel: stop masking signals in create_io_thread()"
commit?

I don't assume signals wanted by userspace should potentially handled in an io_thread...
e.g. things set with fcntl(fd, F_SETSIG,) used together with F_SETLEASE?

metze