linux-kernel - Re: Linux 2.6.26-rc4

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Message-ID: <alpine.LFD.1.10.0806030926330.3473@woody.linux-foundation.org>
Date:	Tue, 3 Jun 2008 09:35:47 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ian Kent <raven@...maw.net>
cc:	Al Viro <viro@...IV.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>, jesper@...gh.cc,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Linux 2.6.26-rc4

On Wed, 4 Jun 2008, Ian Kent wrote:
> 
> The code we're talking about deals with a race between expiring and
> mounting an autofs mount point at the same time. 
> 
> I'll have a closer look and see if I can make it work without turning
> the dentry negative.

Hmm.

Can you walk me through this?

If the dentry is unhashed, it means that it _either_

 - has already been deleted (rmdir'ed) or d_invalidate()'d. Right?

   I don't see why you should ever return the dentry in this case..

 - or it has not yet been hashed at all

   But then d_inode should be NULL too, no?

Anyway, as far as I can tell, you should handle the race between expiring 
and re-mounting not by unhashing at expire time (which causes these kinds 
of problems), but by setting a bit in the dentry and using the dentry 
"revalidate()" callback to wait for the revalidate.

But I don't know autofs4, so you probably have some reason. Could you 
explain it?

		Linus
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