Re: 3.14-rc2 XFS backtrace because irqs_disabled.

Al Viro
2014-02-15T15:36:37Z

On Sat, Feb 15, 2014 at 03:22:51PM +0000, Al Viro wrote:
> 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.

Ouch... I think I see what you mean. Let me see if I got it right:
timer->sigq is *not* freed by collect_signal(); it's done by
release_posix_timer() instead, under siglock. Frankly, this
/*
* If it is queued it will be freed when dequeued,
* like the "regular" sigqueue.
*/
if (!list_empty(&q->list))
q = NULL;
in sigqueue_free() smells like it's asking for races. Sigh...