From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753553Ab2DRArK (ORCPT ); Tue, 17 Apr 2012 20:47:10 -0400 Received: from fieldses.org ([174.143.236.118]:46208 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752229Ab2DRArJ (ORCPT ); Tue, 17 Apr 2012 20:47:09 -0400 Date: Tue, 17 Apr 2012 20:47:06 -0400 From: "J. Bruce Fields" To: Linus Torvalds Cc: Al Viro , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [git pull] vfs and fs fixes Message-ID: <20120418004706.GA1924@fieldses.org> References: <20120417052511.GU6589@ZenIV.linux.org.uk> <20120417180129.GW6589@ZenIV.linux.org.uk> <20120417182825.GX6589@ZenIV.linux.org.uk> <20120417211419.GC27426@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 17, 2012 at 03:08:26PM -0700, Linus Torvalds wrote: > On Tue, Apr 17, 2012 at 2:14 PM, J. Bruce Fields wrote: > > On Tue, Apr 17, 2012 at 07:28:26PM +0100, Al Viro wrote:> > > Maybe instead I could continue using the i_mutex but handle rename some > > other way; e.g. in delegation code: > > > >        if (!mutex_trylock(inode->i_mutex)) > >                return -EAGAIN; > >        if (atomic_read(inode->i_renames_in_progress)) > >                return -EAGAIN; > > > > and add an > > > >        atomic_inc(inode->i_renames_in_progress); > >        atomic_dec(inode->i_renames_in_progress); > > > > pair around rename. > > Please don't make up your own locking. Plus it's broken anyway, since > a rename could come in directly after your atomic_read (and this is > *why* people shouldn't make up their own locks - they are invariably > broken). Doh, yes, sounds like a good rule. (I was misremembering some previous attempt at this--which admittedly may just have failed in some more complicated way.) --b. > > Or I could increment that counter for all the conflicting operations and > > rely on it instead of the i_mutex.  I was trying to avoid adding > > something like that (an inc, a dec, another error path) to every > > operation.  And hoping to avoid adding another field to struct inode. > > Oh well. > > We could just say that we can do a double inode lock, but then > standardize on the order. And the only sane order is comparing inode > pointers, not inode numbers like ext4 apparently does. > > With a standard order, I don't think it would be at all wrong to just > take the inode lock on rename. > > Linus