From: Oleg Nesterov <oleg@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Matt Fleming <matt@codeblueprint.co.uk>,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [patch V2 3/3] signal: Allow tasks to cache one sigqueue struct
Date: Fri, 12 Mar 2021 17:18:31 +0100 [thread overview]
Message-ID: <20210312161830.GA27820@redhat.com> (raw)
In-Reply-To: <20210312113540.7byffvc46cgj75ah@linutronix.de>
On 03/12, Sebastian Andrzej Siewior wrote:
>
> On 2021-03-11 14:20:39 [+0100], Thomas Gleixner wrote:
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -433,7 +433,11 @@ static struct sigqueue *
> > rcu_read_unlock();
> >
> > if (override_rlimit || likely(sigpending <= task_rlimit(t, RLIMIT_SIGPENDING))) {
> > - q = kmem_cache_alloc(sigqueue_cachep, gfp_flags);
> > + /* Preallocation does not hold sighand::siglock */
> > + if (sigqueue_flags || !t->sigqueue_cache)
> > + q = kmem_cache_alloc(sigqueue_cachep, gfp_flags);
> > + else
> > + q = xchg(&t->sigqueue_cache, NULL);
>
> Could it happen that two tasks saw t->sigqueue_cache != NULL, the first
> one got the pointer via xchg() and the second got NULL via xchg()?
It is called with sighand::siglock held, we don't even need xchg().
Oleg.
next prev parent reply other threads:[~2021-03-12 16:19 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-11 13:20 [patch V2 0/3] signals: Allow caching one sigqueue object per task Thomas Gleixner
2021-03-11 13:20 ` [patch V2 1/3] signal: Provide and use exit_task_sighand() Thomas Gleixner
2021-03-11 13:20 ` [patch V2 2/3] signal: Hand SIGQUEUE_PREALLOC flag to __sigqueue_alloc() Thomas Gleixner
2021-03-11 13:20 ` [patch V2 3/3] signal: Allow tasks to cache one sigqueue struct Thomas Gleixner
2021-03-12 11:35 ` Sebastian Andrzej Siewior
2021-03-12 16:18 ` Oleg Nesterov [this message]
2021-03-12 19:25 ` Thomas Gleixner
2021-03-12 16:11 ` Oleg Nesterov
2021-03-12 19:26 ` Thomas Gleixner
2021-03-12 21:13 ` Thomas Gleixner
2021-03-13 11:17 ` [patch V3 " Thomas Gleixner
2021-03-13 16:49 ` [patch V2 " Oleg Nesterov
2021-03-16 12:36 ` Thomas Gleixner
2021-03-11 21:13 ` [patch V2 0/3] signals: Allow caching one sigqueue object per task Eric W. Biederman
2021-03-12 20:02 ` Thomas Gleixner
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