linux-kernel - Re: possible deadlock in blk_trace

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Date:   Sun, 3 Dec 2017 12:24:34 -0800
From:   Eric Biggers <ebiggers3@...il.com>
To:     syzbot 
        <bot+583353673e394aa41e5fb68ddc8b8d9d5c8d576f@...kaller.appspotmail.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        rostedt@...dmis.org, syzkaller-bugs@...glegroups.com
Subject: Re: possible deadlock in blk_trace_remove

On Sun, Nov 19, 2017 at 02:36:01AM -0800, syzbot wrote:
> Hello,
> 
> syzkaller hit the following crash on
> d9e0e63d9a6f88440eb201e1491fcf730272c706
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> 
> Unfortunately, I don't have any reproducer for this bug yet.
> 
> 
> Use struct sctp_sack_info instead
> 
> ============================================
> WARNING: possible recursive locking detected
> 4.14.0-rc8-next-20171110+ #40 Not tainted
> --------------------------------------------
> syz-executor6/21462 is trying to acquire lock:
>  (&q->blk_trace_mutex){+.+.}, at: [<ffffffff81760261>]
> blk_trace_remove+0x21/0x40 kernel/trace/blktrace.c:373
> 
> but task is already holding lock:
>  (&q->blk_trace_mutex){+.+.}, at: [<ffffffff81763b38>]
> blk_trace_setup+0x38/0x70 kernel/trace/blktrace.c:606
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:

#syz fix: blktrace: fix trace mutex deadlock