linux-kernel - Re: 2.6.21-rc3 snd-usb-audio lockdep report.

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Message-ID: <s5h6496sohu.wl%tiwai@suse.de>
Date:	Mon, 12 Mar 2007 12:14:05 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Dave Jones <davej@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-rc3 snd-usb-audio lockdep report.

At Sat, 10 Mar 2007 00:31:33 -0500,
Dave Jones wrote:
> 
> =============================================
> [ INFO: possible recursive locking detected ]
> 2.6.20-1.2962.fc7 #1
> ---------------------------------------------
> rosegardenseque/5229 is trying to acquire lock:
>  (&grp->list_mutex){----}, at: [<ffffffff881d4352>] snd_seq_deliver_event+0x93/0x173 [snd_seq]
> 
> but task is already holding lock:
>  (&grp->list_mutex){----}, at: [<ffffffff881d4352>] snd_seq_deliver_event+0x93/0x173 [snd_seq]
> 
> other info that might help us debug this:
> 1 lock held by rosegardenseque/5229:
>  #0:  (&grp->list_mutex){----}, at: [<ffffffff881d4352>] snd_seq_deliver_event+0x93/0x173 [snd_seq]

Hm, these are read-only so they should never conflict.
Is there a better workaround than *_non_owner()?


Takashi

diff -r a8aa25c670eb sound/core/seq/seq_clientmgr.c
--- a/sound/core/seq/seq_clientmgr.c	Mon Mar 12 11:39:01 2007 +0100
+++ b/sound/core/seq/seq_clientmgr.c	Mon Mar 12 12:12:44 2007 +0100
@@ -672,7 +672,7 @@ static int deliver_to_subscribers(struct
 	if (atomic)
 		read_lock(&grp->list_lock);
 	else
-		down_read(&grp->list_mutex);
+		down_read_non_owner(&grp->list_mutex);
 	list_for_each_entry(subs, &grp->list_head, src_list) {
 		event->dest = subs->info.dest;
 		if (subs->info.flags & SNDRV_SEQ_PORT_SUBS_TIMESTAMP)
@@ -690,7 +690,7 @@ static int deliver_to_subscribers(struct
 	if (atomic)
 		read_unlock(&grp->list_lock);
 	else
-		up_read(&grp->list_mutex);
+		up_read_non_owner(&grp->list_mutex);
 	*event = event_saved; /* restore */
 	snd_seq_port_unlock(src_port);
 	return (err < 0) ? err : num_ev;
-
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