linux-kernel - Re: [PATCH] Improve mutex documentation

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Date:   Thu, 15 Mar 2018 16:23:09 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, tj@...nel.org,
        cl@...ux.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] Improve mutex documentation

On 15.03.2018 16:18, Matthew Wilcox wrote:
> On Thu, Mar 15, 2018 at 03:12:30PM +0300, Kirill Tkhai wrote:
>>> +/**
>>> + * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
>>
>> Shouldn't we clarify that fatal signals are SIGKILL only?
> 
> It's more complicated than it might seem (... welcome to signal handling!)
> If you send SIGINT to a task that's waiting on a mutex_killable(), it will
> still die.  I *think* that's due to the code in complete_signal():
> 
>         if (sig_fatal(p, sig) &&
>             !(signal->flags & SIGNAL_GROUP_EXIT) &&
>             !sigismember(&t->real_blocked, sig) &&
>             (sig == SIGKILL || !p->ptrace)) {
> ...
>                                 sigaddset(&t->pending.signal, SIGKILL);
> 
> You're correct that this code only checks for SIGKILL, but any fatal
> signal will result in the signal group receiving SIGKILL.
> 
> Unless I've misunderstood, and it wouldn't be the first time I've
> misunderstood signal handling.

Sure, thanks for the explanation.

Kirill