snd_pcm lockdep report from 3.3-rc6

DISCUSSION Dave Jones 3 participants 6 messages Mar 12, 2012 – Jun 8, 2012 Sound

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Dave Jones

author

2012-03-12 14:35 UTC #0 lore raw

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

Takashi Iwai

2012-03-12 17:42 UTC #1 lore raw

Hi Dave,

At Mon, 12 Mar 2012 10:35:15 -0400,

Quoted 76 lines · Dave Jones

I just hit this..

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;
}

Quoted 1 line

Should that trylock be on self_group.lock ?

No, the check above should be correct. The code tries to re-lock when the stream is linked like group-lock -> stream-lock.

However, that code is known to be too tricky and messy for long time. It'd be really better to get rid of this complexity. I tried some times but failed to reach to the final goal due to lack of time.

OK, let me respin my old patch. The refreshed one is attached below. (Note that it's totally untested. I have to leave my office now,
sorry for that. Let me know if the wonder happens and it works :)

thanks,

Takashi

---
From: Takashi Iwai <[email protected]>
Subject: [PATCH] ALSA: pcm - Simplify linked PCM substream spinlocks

The spinlocks held for PCM substreams have been always messy. For the better concurrent accessibility, we took always the substream's lock first. When substreams are linked, we need a group-wide lock, but this should be applied outside substream's lock. So, we unlock the substream's lock first, then do locks twice.

This scheme is known to be problematic with lockdep. Maybe because the nested lock isn't marked properly, and partly because the lock and unlock sequences are different (A/B -> A/B).

This patch tries to simplify the scheme. Instead of holding the substream's lock, we take the group lock always at first. A drawback of this is that the access to the individual substream in a same group won't be allowed any longer. But, the code looks much easier, and likely less buggy.

Note that the group lock is identical with the substream's lock initially before the substream is linked with others. So, in the case of non-linked PCM, the new code behaves exactly same as before.

Signed-off-by Takashi Iwai <[email protected]>

---
 include/sound/pcm.h     |   12 ++++++------
 sound/core/pcm_native.c |   36 ++++++++++++++----------------------
 2 files changed, 20 insertions(+), 28 deletions(-)

include/sound/pcm.h +6 -6

index 0cf91b2..d634dcc 100644
@@ -531,36 +531,36 @@ static inline int snd_pcm_stream_linked(struct snd_pcm_substream *substream)
 static inline void snd_pcm_stream_lock(struct snd_pcm_substream *substream)
 {
 	read_lock(&snd_pcm_link_rwlock);
-	spin_lock(&substream->self_group.lock);
+	spin_lock(&substream->group->lock);
 }
 
 static inline void snd_pcm_stream_unlock(struct snd_pcm_substream *substream)
 {
-	spin_unlock(&substream->self_group.lock);
+	spin_unlock(&substream->group->lock);
 	read_unlock(&snd_pcm_link_rwlock);
 }
 
 static inline void snd_pcm_stream_lock_irq(struct snd_pcm_substream *substream)
 {
 	read_lock_irq(&snd_pcm_link_rwlock);
-	spin_lock(&substream->self_group.lock);
+	spin_lock(&substream->group->lock);
 }
 
 static inline void snd_pcm_stream_unlock_irq(struct snd_pcm_substream *substream)
 {
-	spin_unlock(&substream->self_group.lock);
+	spin_unlock(&substream->group->lock);
 	read_unlock_irq(&snd_pcm_link_rwlock);
 }
 
 #define snd_pcm_stream_lock_irqsave(substream, flags) \
 do { \
 	read_lock_irqsave(&snd_pcm_link_rwlock, (flags)); \
-	spin_lock(&substream->self_group.lock); \
+	spin_lock(&substream->group->lock); \
 } while (0)
 
 #define snd_pcm_stream_unlock_irqrestore(substream, flags) \
 do { \
-	spin_unlock(&substream->self_group.lock); \
+	spin_unlock(&substream->group->lock); \
 	read_unlock_irqrestore(&snd_pcm_link_rwlock, (flags)); \
 } while (0)

sound/core/pcm_native.c +14 ~~-22~~

index 25ed9fe..c5f28ed 100644
@@ -712,7 +712,7 @@ static int snd_pcm_action_group(struct action_ops *ops,
 	int res = 0;
 
 	snd_pcm_group_for_each_entry(s, substream) {
-		if (do_lock && s != substream)
+		if (do_lock)
 			spin_lock_nested(&s->self_group.lock,
 					 SINGLE_DEPTH_NESTING);
 		res = ops->pre_action(s, state);

@@ -740,8 +740,7 @@ static int snd_pcm_action_group(struct action_ops *ops,
 	if (do_lock) {
 		/* unlock streams */
 		snd_pcm_group_for_each_entry(s1, substream) {
-			if (s1 != substream)
-				spin_unlock(&s1->self_group.lock);
+			spin_unlock(&s1->self_group.lock);
 			if (s1 == s)	/* end */
 				break;
 		}

@@ -779,13 +778,7 @@ static int snd_pcm_action(struct action_ops *ops,
 	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);
 	}

@@ -801,19 +794,13 @@ static int snd_pcm_action_lock_irq(struct action_ops *ops,
 {
 	int res;
 
-	read_lock_irq(&snd_pcm_link_rwlock);
+	snd_pcm_stream_lock_irq(substream);
 	if (snd_pcm_stream_linked(substream)) {
-		spin_lock(&substream->group->lock);
-		spin_lock(&substream->self_group.lock);
 		res = snd_pcm_action_group(ops, substream, state, 1);
-		spin_unlock(&substream->self_group.lock);
-		spin_unlock(&substream->group->lock);
 	} else {
-		spin_lock(&substream->self_group.lock);
 		res = snd_pcm_action_single(ops, substream, state);
-		spin_unlock(&substream->self_group.lock);
 	}
-	read_unlock_irq(&snd_pcm_link_rwlock);
+	snd_pcm_stream_unlock_irq(substream);
 	return res;
 }

@@ -1586,12 +1573,18 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
 	struct file *file;
 	struct snd_pcm_file *pcm_file;
 	struct snd_pcm_substream *substream1;
+	struct snd_pcm_group *group;
 
 	file = snd_pcm_file_fd(fd);
 	if (!file)
 		return -EBADFD;
 	pcm_file = file->private_data;
 	substream1 = pcm_file->substream;
+	group = kmalloc(sizeof(*group), GFP_KERNEL);
+	if (!group) {
+		res = -ENOMEM;
+		goto _nolock;
+	}
 	down_write(&snd_pcm_link_rwsem);
 	write_lock_irq(&snd_pcm_link_rwlock);
 	if (substream->runtime->status->state == SNDRV_PCM_STATE_OPEN ||

@@ -1604,11 +1597,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
 		goto _end;
 	}
 	if (!snd_pcm_stream_linked(substream)) {
-		substream->group = kmalloc(sizeof(struct snd_pcm_group), GFP_ATOMIC);
-		if (substream->group == NULL) {
-			res = -ENOMEM;
-			goto _end;
-		}
+		substream->group = group;
 		spin_lock_init(&substream->group->lock);
 		INIT_LIST_HEAD(&substream->group->substreams);
 		list_add_tail(&substream->link_list, &substream->group->substreams);

@@ -1620,7 +1609,10 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
  _end:
 	write_unlock_irq(&snd_pcm_link_rwlock);
 	up_write(&snd_pcm_link_rwsem);
+ _nolock:
 	fput(file);
+	if (res < 0)
+		kfree(group);
 	return res;
 }

Signature · 1 line

1.7.9.2

Dave Jones

author

2012-03-12 17:48 UTC #2 lore raw

Quoted 10 lines · Takashi Iwai

No, the check above should be correct. The code tries to re-lock when the stream is linked like group-lock -> stream-lock.
However, that code is known to be too tricky and messy for long time. It'd be really better to get rid of this complexity. I tried some times but failed to reach to the final goal due to lack of time.
OK, let me respin my old patch. The refreshed one is attached below. (Note that it's totally untested. I have to leave my office now,
sorry for that. Let me know if the wonder happens and it works :)

it certainly makes the code look a little simpler! I'll run with it for a while, and see if anything falls out.

thanks,

Dave

Dave Jones

author

2012-03-20 17:13 UTC #3 lore raw

In reply to Takashi Iwai

Quoted 7 lines · Takashi Iwai

However, that code is known to be too tricky and messy for long time. It'd be really better to get rid of this complexity. I tried some times but failed to reach to the final goal due to lack of time.
OK, let me respin my old patch. The refreshed one is attached below. (Note that it's totally untested. I have to leave my office now,
sorry for that. Let me know if the wonder happens and it works :)

I thought I was going crazy when I still saw the same trace, and made sure the patch was actually applied, and rebuilt the kernel. Seems this patch doesn't fix this.

The trace is slightly different (one fewer lock taken)..

Dave

=============================================
[ INFO: possible recursive locking detected ]
3.3.0+ #15 Not tainted
---------------------------------------------
pulseaudio/1269 is trying to acquire lock:
(&(&substream->self_group.lock)->rlock/1){......}, at: [<ffffffffa0476c00>] snd_pcm_action_group+0x90/0x250 [snd_pcm]

but task is already holding lock:
(&(&substream->self_group.lock)->rlock/1){......}, at: [<ffffffffa0476c00>] snd_pcm_action_group+0x90/0x250 [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

3 locks held by pulseaudio/1269:

 #0:  (snd_pcm_link_rwlock){......}, at: [<ffffffffa0478ac9>] snd_pcm_drop+0x49/0xe0 [snd_pcm]
 #1:  (&(&substream->group->lock)->rlock){......}, at: [<ffffffffa0478ad5>] snd_pcm_drop+0x55/0xe0 [snd_pcm]
 #2:  (&(&substream->self_group.lock)->rlock/1){......}, at: [<ffffffffa0476c00>] snd_pcm_action_group+0x90/0x250 [snd_pcm]

stack backtrace:
Pid: 1269, comm: pulseaudio Not tainted 3.3.0+ #15
Call Trace:
 [<ffffffff810cee37>] __lock_acquire+0xe47/0x1bb0
 [<ffffffff81023322>] ? native_sched_clock+0x22/0x80
 [<ffffffff810d02bd>] lock_acquire+0x9d/0x220
 [<ffffffffa0476c00>] ? snd_pcm_action_group+0x90/0x250 [snd_pcm]
 [<ffffffff810ca8be>] ? put_lock_stats+0xe/0x40
 [<ffffffff816a1a1d>] _raw_spin_lock_nested+0x4d/0x90
 [<ffffffffa0476c00>] ? snd_pcm_action_group+0x90/0x250 [snd_pcm]
 [<ffffffffa0476c00>] snd_pcm_action_group+0x90/0x250 [snd_pcm]
 [<ffffffff812c5a46>] ? avc_has_perm_noaudit+0x46/0x500
 [<ffffffffa0477f03>] snd_pcm_action+0x23/0x40 [snd_pcm]
 [<ffffffffa0477f3a>] snd_pcm_stop+0x1a/0x20 [snd_pcm]
 [<ffffffffa0478aef>] snd_pcm_drop+0x6f/0xe0 [snd_pcm]
 [<ffffffffa047ad08>] snd_pcm_common_ioctl1+0x668/0xc30 [snd_pcm]
 [<ffffffffa047b727>] snd_pcm_playback_ioctl1+0x147/0x2e0 [snd_pcm]
 [<ffffffff812c839c>] ? file_has_perm+0xdc/0xf0
 [<ffffffffa047b8f4>] snd_pcm_playback_ioctl+0x34/0x40 [snd_pcm]
 [<ffffffff811d4858>] do_vfs_ioctl+0x98/0x570
 [<ffffffff811d4dc1>] sys_ioctl+0x91/0xa0
 [<ffffffff816aa3e9>] system_call_fastpath+0x16/0x1b

Dave Jones

author

2012-06-08 03:23 UTC #4 lore raw

In reply to Takashi Iwai

On Mon, Mar 12, 2012 at 06:42:48PM +0100, Takashi Iwai wrote:

Hi Takashi,

Quoted 77 lines

Quoted 72 lines
[ 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;
}
Quoted 1 line
Should that trylock be on self_group.lock ?
No, the check above should be correct. The code tries to re-lock when the stream is linked like group-lock -> stream-lock.

Quoted 7 lines

However, that code is known to be too tricky and messy for long time. It'd be really better to get rid of this complexity. I tried some times but failed to reach to the final goal due to lack of time.
OK, let me respin my old patch. The refreshed one is attached below. (Note that it's totally untested. I have to leave my office now,
sorry for that. Let me know if the wonder happens and it works :)

I'm not sure if I got back to you on this, but that patch did nothing to change this for me, and I still see this on 3.5-rc1

Dave

Maciej Rutecki

2012-03-18 19:31 UTC #5 lore raw

In reply to Dave Jones

Quoted 81 lines · On poniedziałek, 12 marca 2012 o 15:35:15 Dave Jones wrote:

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;
}

Quoted 3 lines

Should that trylock be on self_group.lock ?
Dave

I created a Bugzilla entry at
https://bugzilla.kernel.org/show_bug.cgi?id=42958
for your bug/regression report, please add your address to the CC list in there, thanks!

Signature · 2 lines

Maciej Rutecki
http://www.mrutecki.pl