From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755799Ab0F2UjI (ORCPT ); Tue, 29 Jun 2010 16:39:08 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38450 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755935Ab0F2UjF convert rfc822-to-8bit (ORCPT ); Tue, 29 Jun 2010 16:39:05 -0400 MIME-Version: 1.0 In-Reply-To: References: <20100608004102.GQ31073@ZenIV.linux.org.uk> <87pqzrexon.fsf@linux.vnet.ibm.com> <871vbwe6lp.fsf@linux.vnet.ibm.com> Date: Tue, 29 Jun 2010 13:38:57 -0700 Message-ID: Subject: Re: [V9fs-developer] [GIT PULL] 9p file system bug fixes for 2.6.35-rc2 From: Linus Torvalds To: Eric Van Hensbergen Cc: Al Viro , V9FS Developers , linux-kernel Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 29, 2010 at 1:18 PM, Eric Van Hensbergen wrote: > > Does this approach satisfy your concerns?  We've been going over > several different options on how to proceed, but this seems to be the > best option. Using a p9fs rename lock does seem to be a reasonable option. That said, the patch itself seems to not be valid. You drop the lock too early in v9fs_fid_lookup() as far as I can tell. You then re-take it before doing that whole for (d = dentry, i = (n-1); i >= 0; i--, d = d->d_parent) loop with it held again, but that's totally bogus - because you dropped the lock, your 'n-1' count has absolutely no meaning any more, since a cross-directory rename might have changed the depth of the thing in the meantime. And if the depth changes, you aren't at all guaranteed to stay on the same p9fs filesystem, so now you're doing that d_parent access without the proper locking (sure: you hold the rename lock, but it's not at all guaranteed that the rename lock is the _right_ lock any more as you traverse the list down!) But I didn't look deeply at the patch. There might be some reason why it's safe (I doubt it, though), and there might be other places where you do the same. But in general, dropping and re-taking a lock is a bad idea. If you dropped the lock, you can't depend on anything you found out while having held it. Linus