linux-kernel - Re: [PATCH 12/14 UPDATED] sysfs: implement sysfs_dirent active reference and immediate disconnect

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Message-ID: <20070411101359.GF10619@htj.dyndns.org>
Date:	Wed, 11 Apr 2007 19:13:59 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	gregkh@...e.de, maneesh@...ibm.com, dmitry.torokhov@...il.com,
	oneukum@...e.de, rpurdie@...ys.net, James.Bottomley@...elEye.com,
	stern@...land.harvard.edu, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 12/14 UPDATED] sysfs: implement sysfs_dirent active reference and immediate disconnect

On Wed, Apr 11, 2007 at 06:26:42PM +0900, Tejun Heo wrote:
> Hello,
> 
> Cornelia Huck wrote:
> > =======================================================
> > [ INFO: possible circular locking dependency detected ]
> > 2.6.21-rc6-ge666c753-dirty #54
> > -------------------------------------------------------
> > kslowcrw/64 is trying to acquire lock:
> >  (&sch->reg_mutex){--..}, at: [<00000000004233b2>] mutex_lock+0x3e/0x4c
> > 
> > but task is already holding lock:
> >  (&sd->s_active){----}, at: [<0000000000209578>] remove_dir+0xec/0x144
> > 
> > which lock already depends on the new lock.
> 
> This is probably because s_active has different write locked and
> unlocked by different threads but it doesn't tell lockdep about it.
> I'll read lockdep docs and update it.

Does this patch fix the problem?

Index: work/fs/sysfs/dir.c
===================================================================
--- work.orig/fs/sysfs/dir.c	2007-04-11 19:12:02.000000000 +0900
+++ work/fs/sysfs/dir.c	2007-04-11 19:12:12.000000000 +0900
@@ -26,7 +26,8 @@ void release_sysfs_dirent(struct sysfs_d
 	 * locked.  If @sd is cursor for directory walk or being
 	 * released prematurely, s_active has no reader or writer.
 	 */
-	down_write_trylock(&sd->s_active);
+	if (!down_write_trylock(&sd->s_active))
+		rwsem_acquire(&sd->s_active.dep_map, 0, 0, _RET_IP_);
 	up_write(&sd->s_active);
 
 	if (sd->s_type & SYSFS_KOBJ_LINK)
Index: work/fs/sysfs/sysfs.h
===================================================================
--- work.orig/fs/sysfs/sysfs.h	2007-04-11 19:12:02.000000000 +0900
+++ work/fs/sysfs/sysfs.h	2007-04-11 19:12:03.000000000 +0900
@@ -171,6 +171,7 @@ static inline void sysfs_put_active_two(
 static inline void sysfs_deactivate(struct sysfs_dirent *sd)
 {
 	down_write(&sd->s_active);
+	rwsem_release(&sd->s_active.dep_map, 1, _RET_IP_);
 }
 
 static inline int sysfs_is_shadowed_inode(struct inode *inode)
-
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