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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 15:27:00 +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: <20140215052531.GX18016@xxxxxxxxxxxxxxxxxx>
References: <20140212042215.GN18016@xxxxxxxxxxxxxxxxxx> <20140212054043.GB13997@dastard> <CA+55aFxy2t7bnCUc-DhhxYxsZ0+GwL9GuQXRYtE_VzqZusmB9A@xxxxxxxxxxxxxx> <20140212113928.GO18016@xxxxxxxxxxxxxxxxxx> <CA+55aFywwx0Q8xK2GJiRJ+FV7PQEKoBRxDUxW4052FVyd5XOpg@xxxxxxxxxxxxxx> <20140212211421.GP18016@xxxxxxxxxxxxxxxxxx> <CA+55aFyobyUNFo=3rpdbxTqgV7OQetCKbCfwEEbgxUcT-1+30w@xxxxxxxxxxxxxx> <20140213174020.GA14455@xxxxxxxxxx> <CA+55aFxwozCQ05axLB02R3huX8sj=20EoFfw0cSDDL8fBE_Y6Q@xxxxxxxxxxxxxx> <20140215052531.GX18016@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
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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