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

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Message-ID: <20140215142700.GA15540@redhat.com>
Date:	Sat, 15 Feb 2014 15:27:00 +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:
>
> OK, _very_ preliminary patch follows.  It's uglier than it has to

And I'm afraid it needs more uglifications...

> +void dismiss_siginfo(ksiginfo_t *info)
> +{
> +	if (info->q)
> +		__sigqueue_free(info->q);
> +	info->q = NULL;
> +}

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().

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.

Oleg.

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