From: Theodore Tso Subject: Re: potential regression in ext[34] call to __page_symlink()? Date: Tue, 28 Oct 2008 22:40:48 -0400 Message-ID: <20081029024048.GB3766@mit.edu> References: <170fa0d20810281711s2a508ed2o1af0db30733e8d2d@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, Nick Piggin , Kirill Korotaev To: Mike Snitzer Return-path: Received: from www.church-of-our-saviour.org ([69.25.196.31]:49373 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752314AbYJ2Ckv (ORCPT ); Tue, 28 Oct 2008 22:40:51 -0400 Content-Disposition: inline In-Reply-To: <170fa0d20810281711s2a508ed2o1af0db30733e8d2d@mail.gmail.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Oct 28, 2008 at 08:11:48PM -0400, Mike Snitzer wrote: > The gfp_mask that is passed to __page_symlink() is being completely > dropped on the floor. Historically this mask was at least used by > ext3 and ext4 to avoid recursing back into the FS from within a > journal transaction; Kirill fixed that issue with this commit: > 0adb25d2e71ab047423d6fc63d5d184590d0a66f > > I'm quite naive when it comes to Nick's relatively new (>= 2.6.24) AOP > pagecache_write_{begin,end} code that motivated __page_symlink to > change with this commit: > afddba49d18f346e5cc2938b6ed7c512db18ca68 > > Nick's change clearly did away with using the explicitly passed > gfp_mask in __page_symlink(). > So at a minimum it would seem __page_symlink() now has an unused > parameter that should be removed. > > But a more serious concern would be: have ext[34]_symlink() regressed > to being susceptible to the bug that Kirill fixed some time ago? Yeah, I think this would be a potential problem for ext3/4. Looks like pagemap_write_begin() should take a gfp_mask argument, and then pass it down through to __grab_cache_page(), which should then call __page_cache_alloc() instead of _page_cache_alloc(). Then __page_symlink() can actually pass in its gfp_mask to pagemap_write_begin(). Nick, do you agree? - Ted