From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: [PATCH] vfs: fix race in rcu lookup of pruned dentry Date: Wed, 20 Jul 2011 10:47:21 +1000 Message-ID: <20110720104721.03a2a2f0@notabene.brown> References: <20110718194703.GI11013@ZenIV.linux.org.uk> <20110719234550.GR11013@ZenIV.linux.org.uk> <20110719235215.GS11013@ZenIV.linux.org.uk> <20110719235515.GT11013@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Linus Torvalds , Hugh Dickins , Andrew Morton , Nick Piggin , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Al Viro Return-path: In-Reply-To: <20110719235515.GT11013@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 20 Jul 2011 00:55:15 +0100 Al Viro wrote: > On Wed, Jul 20, 2011 at 12:52:16AM +0100, Al Viro wrote: > > On Wed, Jul 20, 2011 at 12:45:51AM +0100, Al Viro wrote: > > > > > You know what... I doubt that you want to mess with ->d_seq checks here. > > > It's definitely not Hugh's bug (unless he has bindings somewhere odd) and > > > both ->mnt_mountpoint and ->mnt_root are pinned (and we are holding > > > vfsmount_lock anyway). *inode assignment too early is a real bug, indeed, > > > and we want to assign nd->seq if we cross mountpoint as both versions do, > > > but check just before that is, in the best case, BUG_ON() fodder. We'd > > > just found a vfsmount with ->mnt_mountpoint equal to path->dentry; it *can't* > > > be stale, or we have a really nasty problem anyway. > > > > Kudos to neilb for spotting the pointless check, BTW; and no, his theory > > that it might be needed since we could race with umount() is wrong - due to > > vfsmount_lock being held. Thanks.. but that patch seems to introduce an unused variable "seq". NeilBrown > > Updated, pushed. Please, pull from the usual place ( > git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6.git/ for-linus > ). > > Shortlog: > Al Viro (1): > Fix cifs_get_root() > > Linus Torvalds (1): > vfs: fix race in rcu lookup of pruned dentry > > Diffstat: > fs/cifs/cifsfs.c | 100 +++++++++++++++-------------------------------------- > fs/namei.c | 10 +++++- > 2 files changed, 38 insertions(+), 72 deletions(-)