From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: next-20130117 - kernel BUG with aio Date: Thu, 24 Jan 2013 14:13:52 -0800 Message-ID: <20130124221352.GK26407@google.com> References: <3544.1358774694@turing-police.cc.vt.edu> <2553.1358890098@turing-police.cc.vt.edu> <13450.1359048141@turing-police.cc.vt.edu> <20130124211850.GH26407@google.com> <20130124132759.c892fb4c.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Valdis.Kletnieks@vt.edu, Hillf Danton , Benjamin LaHaise , linux-kernel@vger.kernel.org, linux-aio@kvack.org, zab@zabbo.net, linux-fsdevel@vger.kernel.org To: Andrew Morton , jack@suse.cz, tytso@mit.edu Return-path: Received: from mail-pb0-f53.google.com ([209.85.160.53]:64283 "EHLO mail-pb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755400Ab3AXWN4 (ORCPT ); Thu, 24 Jan 2013 17:13:56 -0500 Received: by mail-pb0-f53.google.com with SMTP id un1so5037476pbc.26 for ; Thu, 24 Jan 2013 14:13:55 -0800 (PST) Content-Disposition: inline In-Reply-To: <20130124132759.c892fb4c.akpm@linux-foundation.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Thu, Jan 24, 2013 at 01:27:59PM -0800, Andrew Morton wrote: > Please also take a look at Jan's recent > http://www.spinics.net/lists/linux-fsdevel/msg61738.html and have a > think about how this plays with your patchset. I can't think of any possible interactions - none of my aio stuff messes with the way the fput() happens; the aio code does call fput() when the kiocb is freed and my patches do touch _that_ code but none of the behaviour there changes. Might be worth documenting this though, I can't think of any reason it'd be obvious looking at the aio code that the fput() has to happen after aio_complete(). As with the bugs I just sent you patches for it's not terribly clear who owns what in the kiocb when. Reading those patches though - the main change is to call inode_dio_done() before calling aio_complete(). All inode_dio_done() does though is issue a wakeup - to whatever called inode_dio_wait(). That means whatever called inode_dio_wait() needs its own ref on the inode, and from a cursory glance at the code it is _not_ at all clear to me that's the case - if inode_dio_wait() is merely finishing things for that specific IO that need to be done in process context, I can easily imagine it not being the case. Assuming whatever does call inode_dio_wait() does have its own ref, there was only a real use after free when nothing was waiting on the inode. Similarly for the ext4 code to write unwritten extents - and having seen and helped chase a bug in that code before, that code _definitely_ needs auditing.