3.14-rc2 XFS backtrace because irqs_disabled.

[Al Viro]

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().