From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH 02/46] fs: d_validate fixes Date: Wed, 8 Dec 2010 12:53:44 +1100 Message-ID: <20101208015344.GE29333@dastard> References: <0fff695735c9b652a3f63b8480686c64811e89d0.1290852958.git.npiggin@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Nick Piggin Return-path: Content-Disposition: inline In-Reply-To: <0fff695735c9b652a3f63b8480686c64811e89d0.1290852958.git.npiggin@kernel.dk> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Sat, Nov 27, 2010 at 08:44:32PM +1100, Nick Piggin wrote: > d_validate has been broken for a long time. > > kmem_ptr_validate does not guarantee that a pointer can be dereferenced > if it can go away at any time. Even rcu_read_lock doesn't help, because > the pointer might be queued in RCU callbacks but not executed yet. > > So the parent cannot be checked, nor the name hashed. The dentry pointer > can not be touched until it can be verified under lock. Hashing simply > cannot be used. > > Instead, verify the parent/child relationship by traversing parent's > d_child list. It's slow, but only ncpfs and the destaged smbfs care > about it, at this point. I'd drop the previous revert patch and just convert the RCU hash traversal straight to the d_child traversal code you introduce here. This is a much better explanation of why the d_validate mechanism needs to be changed, and the revert is really an unnecessary extra step... Cheers, Dave. -- Dave Chinner david@fromorbit.com