linux-kernel - Re: [PATCH] autofs4 - remove hashed check in validate

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Message-Id: <20090607220814.cc7519f6.akpm@linux-foundation.org>
Date:	Sun, 7 Jun 2009 22:08:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ian Kent <raven@...maw.net>
Cc:	autofs mailing list <autofs@...ux.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] autofs4 - remove hashed check in validate_wait()

On Mon, 08 Jun 2009 11:25:37 +0800 Ian Kent <raven@...maw.net> wrote:

> The recent ->lookup() deadlock correction required the directory
> inode mutex to be dropped while waiting for expire completion. We
> were concerned about side effects from this change and one has
> been identified.
> 
> When checking if a mount has already completed prior to adding a
> new mount request to the wait queue we check if the dentry is hashed
> and, if so, if it is a mount point. But, if a mount successfully
> completed while we slept on the wait queue mutex the dentry must
> exist for the mount to have completed so the test is not really
> needed.
> 
> Mounts can also be done on top of a global root dentry, so for the
> above case, where a mount request completes and the wait queue entry
> has already been removed, the hashed test returning false can cause
> an incorrect callback to the daemon. Also, d_mountpoint() is not
> sufficient to check if a mount has completed for the multi-mount
> case when we don't have a real mount at the base of the tree.
> 

I've been scratching my head trying to work out if this is a
needed-in-2.6.30 fix, but all I got was a bald spot.  Help?
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