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Re: 3.14-rc2 XFS backtrace because irqs_disabled.

To: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Date: Sat, 15 Feb 2014 19:45:31 +0100
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Dave Jones <davej@xxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140215180520.GC18016@xxxxxxxxxxxxxxxxxx>
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User-agent: Mutt/1.5.18 (2008-05-17)
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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