From: Oleg Nesterov <oleg@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Sasha Levin <sasha.levin@oracle.com>,
linux-kernel@vger.kernel.org, mingo@kernel.org
Subject: Re: [PATCH] signals: work around random wakeups in sigsuspend()
Date: Wed, 27 Jan 2016 22:07:54 +0100 [thread overview]
Message-ID: <20160127210754.GA1593@redhat.com> (raw)
In-Reply-To: <20160127103944.9216fd184af420f0c44603f1@linux-foundation.org>
On 01/27, Andrew Morton wrote:
>
> On Wed, 27 Jan 2016 17:41:54 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
>
> > IOW, signal_pending() is the "special" condition, you do not need to serialize
> > this check with task->state setting, exactly because schedule() knows about the
> > signals.
>
> So it's non-buggy because signal_pending() is special. But it *looks*
> buggy! And there's no comment there explaining why it looks buggy but
> isn't, so someone may later come along and "fix" it for us.
perhaps we can add a comment somewhere in sched.h to explain that a task can
never sleep with task->state == STATE if signal_pending_state(STATE) is true.
Every user of signal_pending() in the wait-event-like loop relies on this well-
known fact. Say, wait_event_interruptible() or __mutex_lock_common().
This is actually more about task->state, not about TIF_SIGPENDING imo.
Oleg.
next prev parent reply other threads:[~2016-01-27 21:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-25 15:21 [PATCH] signals: work around random wakeups in sigsuspend() Sasha Levin
2016-01-25 19:09 ` Oleg Nesterov
2016-01-25 19:37 ` Peter Zijlstra
2016-02-25 3:18 ` Al Viro
2016-02-25 8:11 ` Peter Zijlstra
2016-02-25 17:34 ` Al Viro
2016-01-25 21:32 ` Andrew Morton
2016-01-26 21:10 ` Oleg Nesterov
2016-01-27 8:44 ` Peter Zijlstra
2016-01-27 16:41 ` Oleg Nesterov
2016-01-27 17:54 ` Peter Zijlstra
2016-01-27 18:39 ` Andrew Morton
2016-01-27 21:07 ` Oleg Nesterov [this message]
2016-01-27 17:24 ` Sasha Levin
2016-01-26 6:44 ` Ingo Molnar
2016-01-26 15:05 ` Oleg Nesterov
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