linux-kernel - snd_pcm lockdep report from 3.3-rc6

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Date:	Mon, 12 Mar 2012 10:35:15 -0400
From:	Dave Jones <davej@...hat.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>
Cc:	tiwai@...e.de
Subject: snd_pcm lockdep report from 3.3-rc6

I just hit this..

[ INFO: possible recursive locking detected ]
3.3.0-rc6+ #5 Not tainted
---------------------------------------------
pulseaudio/1306 is trying to acquire lock:
 (&(&substream->self_group.lock)->rlock/1){......}, at: [<ffffffffa0468c0b>] snd_pcm_action_group+0x9b/0x260 [snd_pcm]

but task is already holding lock:
 (&(&substream->self_group.lock)->rlock/1){......}, at: [<ffffffffa0468c0b>] snd_pcm_action_group+0x9b/0x260 [snd_pcm]

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(&substream->self_group.lock)->rlock/1);
  lock(&(&substream->self_group.lock)->rlock/1);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

4 locks held by pulseaudio/1306:
 #0:  (snd_pcm_link_rwlock){......}, at: [<ffffffffa046ab90>] snd_pcm_drop+0x60/0x100 [snd_pcm]
 #1:  (&(&substream->self_group.lock)->rlock){......}, at: [<ffffffffa046ab98>] snd_pcm_drop+0x68/0x100 [snd_pcm]
 #2:  (&(&substream->group->lock)->rlock){......}, at: [<ffffffffa0469ffe>] snd_pcm_action+0x3e/0xb0 [snd_pcm]
 #3:  (&(&substream->self_group.lock)->rlock/1){......}, at: [<ffffffffa0468c0b>] snd_pcm_action_group+0x9b/0x260 [snd_pcm]

stack backtrace:
Pid: 1306, comm: pulseaudio Not tainted 3.3.0-rc6+ #5
Call Trace:
 [<ffffffff810cee87>] __lock_acquire+0xe47/0x1bb0
 [<ffffffff810a62b8>] ? sched_clock_cpu+0xb8/0x130
 [<ffffffff810d030d>] lock_acquire+0x9d/0x220
 [<ffffffffa0468c0b>] ? snd_pcm_action_group+0x9b/0x260 [snd_pcm]
 [<ffffffff810ca91e>] ? put_lock_stats+0xe/0x40
 [<ffffffff8169d3cd>] _raw_spin_lock_nested+0x4d/0x90
 [<ffffffffa0468c0b>] ? snd_pcm_action_group+0x9b/0x260 [snd_pcm]
 [<ffffffffa0468c0b>] snd_pcm_action_group+0x9b/0x260 [snd_pcm]
 [<ffffffffa046a031>] snd_pcm_action+0x71/0xb0 [snd_pcm]
 [<ffffffffa046a08a>] snd_pcm_stop+0x1a/0x20 [snd_pcm]
 [<ffffffffa046abb1>] snd_pcm_drop+0x81/0x100 [snd_pcm]
 [<ffffffffa046cdf8>] snd_pcm_common_ioctl1+0x678/0xc00 [snd_pcm]
 [<ffffffffa046d7d7>] snd_pcm_playback_ioctl1+0x147/0x2e0 [snd_pcm]
 [<ffffffff812c1cbc>] ? file_has_perm+0xdc/0xf0
 [<ffffffffa046d9a4>] snd_pcm_playback_ioctl+0x34/0x40 [snd_pcm]
 [<ffffffff811d2398>] do_vfs_ioctl+0x98/0x570
 [<ffffffff811d2901>] sys_ioctl+0x91/0xa0
 [<ffffffff816a5de9>] system_call_fastpath+0x16/0x1b

I suspect this ..

static int snd_pcm_action(struct action_ops *ops,
                          struct snd_pcm_substream *substream,
                          int state)
{
        int res;

        if (snd_pcm_stream_linked(substream)) {
-->             if (!spin_trylock(&substream->group->lock)) {
                        spin_unlock(&substream->self_group.lock);
                        spin_lock(&substream->group->lock);
                        spin_lock(&substream->self_group.lock);
                }
                res = snd_pcm_action_group(ops, substream, state, 1);
                spin_unlock(&substream->group->lock);
        } else {
                res = snd_pcm_action_single(ops, substream, state);
        }
        return res;
}

Should that trylock be on self_group.lock ?

	Dave
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