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Re: 3.14-rc2 XFS backtrace because irqs_disabled.

To: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Sat, 15 Feb 2014 15:22:51 +0000
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Dave Jones <davej@xxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
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Sender: Al Viro <viro@xxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sat, Feb 15, 2014 at 03:27:00PM +0100, Oleg Nesterov wrote:

> 1. info->q can be already freed if SIGQUEUE_PREALLOC.
> 
>    Once get_signal_to_deliver() or any other caller drops ->siglock
>    another thread can do sys_timer_delete()->sigqueue_free().

How the devil would it find the sucker?  It's off the list already.

> 2. We need to move do_schedule_next_timer() from dequeue_signal()
>    here.
> 
>    Otherwise ->q can be reused/overwritten by the next send_sigqueue()
>    right affter ->siglock is dropped.

Ditto.  We rip them out of queue on collect_signal(); the only thing we do
not do is actual __sigqueue_free().

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