linux-kernel - Re: [PATCH 2.6.24-rc7 2/2] sysfs: fix bugs in sysfs_rename/move

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Date:	Tue, 15 Jan 2008 19:41:58 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tejun Heo <htejun@...il.com>
cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	Gabor Gombas <gombasg@...aki.hu>, Greg KH <greg@...ah.com>,
	Dave Young <hidave.darkstar@...il.com>,
	bluez-devel@...ts.sourceforge.net
Subject: Re: [PATCH 2.6.24-rc7 2/2] sysfs: fix bugs in
 sysfs_rename/move_dir()

On Wed, 16 Jan 2008, Tejun Heo wrote:
>
> * sysfs_move_dir() has an extra dput() on success path.

Are you sure? How did this ever work?

Also, looking at this, I think the "how did this ever work" question is 
answered by "it didn't", but I also think there are still serious problems 
there. Look at

	again:
	        mutex_lock(&old_parent->d_inode->i_mutex);
	        if (!mutex_trylock(&new_parent->d_inode->i_mutex)) {
	                mutex_unlock(&old_parent->d_inode->i_mutex);
	                goto again;
	        }

and wonder what happen sif old_parent == new_parent. Is that trying to 
avoid an ABBA deadlock? Normally you'd do it by ordering the locks, or by 
taking a third lock to guarantee serialization at a higher level (ie the 
"s_vfs_rename_mutex" on the VFS layer)

I'd like to apply these two patches, but I really want to get more of an 
ack for them from somebody like Al, or at least more of an explanation for 
why it's all the right thing.

			Linus
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