linux-kernel - Re: 3.14-rc2 XFS backtrace because irqs

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

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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