linux-kernel - Re: [PATCH] configfs: add missing mutex

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Message-ID: <20070304151659.GA19972@APFDCB5C>
Date:	Mon, 5 Mar 2007 00:16:59 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org, Joel Becker <joel.becker@...cle.com>
Subject: Re: [PATCH] configfs: add missing mutex_unlock()

On Sun, Mar 04, 2007 at 03:10:19PM +0100, Arnd Bergmann wrote:
> On Sunday 04 March 2007 14:38:12 Akinobu Mita wrote:
> > @@ -1168,8 +1168,10 @@ int configfs_register_subsystem(struct c
> >  
> >         err = -ENOMEM;
> >         dentry = d_alloc(configfs_sb->s_root, &name);
> > -       if (!dentry)
> > +       if (!dentry) {
> > +               mutex_unlock(&configfs_sb->s_root->d_inode->i_mutex);
> >                 goto out_release;
> > +       }
> >  
> >         d_add(dentry, NULL);
> 
> This should be changed to jump to a new exit point, before the mutex_unlock
> at the end of the function. Having multiple places in the function that
> release the same lock easily leads to the kind of bug you are fixing here.

Agreed. Please see the patch below (untested).

Index: 2.6-mm/fs/configfs/dir.c
===================================================================
--- 2.6-mm.orig/fs/configfs/dir.c
+++ 2.6-mm/fs/configfs/dir.c
@@ -1169,25 +1169,26 @@ int configfs_register_subsystem(struct c
 	err = -ENOMEM;
 	dentry = d_alloc(configfs_sb->s_root, &name);
 	if (!dentry)
-		goto out_release;
+		goto out_unlock;
 
 	d_add(dentry, NULL);
 
 	err = configfs_attach_group(sd->s_element, &group->cg_item,
 				    dentry);
-	if (!err)
-		dentry = NULL;
-	else
-		d_delete(dentry);
+	if (err)
+		goto out_d_delete;
 
 	mutex_unlock(&configfs_sb->s_root->d_inode->i_mutex);
 
-	if (dentry) {
-	    dput(dentry);
-out_release:
-	    unlink_group(group);
-	    configfs_release_fs();
-	}
+	return 0;
+
+out_d_delete:
+	d_delete(dentry);
+	dput(dentry);
+out_unlock:
+	mutex_unlock(&configfs_sb->s_root->d_inode->i_mutex);
+	unlink_group(group);
+	configfs_release_fs();
 
 	return err;
 }
-
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