linux-kernel - Re: [PATCH 0/3] Fixes for vfs-scale and vfs-automount

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Message-ID: <20110224054701.GU22723@ZenIV.linux.org.uk>
Date:	Thu, 24 Feb 2011 05:47:01 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Ian Kent <raven@...maw.net>
Cc:	Nick Piggin <npiggin@...nel.dk>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	David Howells <dhowells@...hat.com>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH 0/3] Fixes for vfs-scale and vfs-automount

On Thu, Feb 24, 2011 at 03:58:37AM +0000, Al Viro wrote:
> On Thu, Feb 24, 2011 at 11:28:57AM +0800, Ian Kent wrote:
> 
> > Ha, I haven't even turned on my Ultrsparc 2 in months, it's only got an
> > old version of Solaris on it now anyway, ;)
> 
> U60, with lenny (and mainline kernel) on it.  Probably ought to upgrade
> to squeeze one of those days...  It works, all right, but it's only 2-way,
> so reproducing would probably be harder.  Plus the fun of building the tests
> themselves on somewhat different userland...
> 
> Anyway, I wonder why you care about __d_lookup_rcu() and ->d_inode stability;
> d_mountpoint() _is_ stable at that point (we hold vfsmount_lock) and you
> don't seem to look at ->d_inode at all in RCU case.  Note that ->d_automount()
> is never called in RCU case at all; nor is ->lookup() and friends, so you
> really only have ->d_manage() to cope with, what with autofs4 having no
> ->d_revalidate() anymore.

FWIW, can we _ever_ get to __do_follow_link() with link->mnt != nd->path.mnt?
It's probably not what's happening here, or we would've stepped on another
BUG_ON(), but still it might be worth checking...

AFAICS, if we ever get there that way, we are fscked, so the check before
mntget() ought to replaced with BUG_ON(link->mnt != nd->path.mnt)...
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