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Date: Sat, 15 Feb 2014 19:45:31 +0100
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.
Message-ID: <20140215184531.GA27314@redhat.com>
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To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric Sandeen <sandeen@sandeen.net>, Linux Kernel <linux-kernel@vger.kernel.org>, xfs@oss.sgi.com, Dave Jones <davej@redhat.com>, Linus Torvalds <torvalds@linux-foundation.org>

On 02/15, Al Viro wrote:
>
> On Sat, Feb 15, 2014 at 06:43:45PM +0100, Oleg Nesterov wrote:
> > > So basically we want a different condition for "can we just go ahead and
> > > free that sucker", right?  Instead of "it's on the list, shan't free it"
> > > it ought to be something like "it's on the list or it is referenced by
> > > ksiginfo".  Locking will be interesting, though... ;-/
> >
> > I guess yes... send_sigqueue() checks list_empty() too, probably nobody else.
>
> The trouble being, we might end up with
> 	Q picked by collect_signal and and stuff into ksiginfo
> 	Q resubmitted by timer code

In this case the timer code should simply inc ->si_overrun and do nothing.

IOW, list_empty() should be turned into is_queued(), and is_queued()
should be true until dismiss_siginfo() which should also do
do_schedule_next_timer(). I think.

Oleg.

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