Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 30 Jul 2002 17:27:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 30 Jul 2002 17:27:53 -0400 Received: from perninha.conectiva.com.br ([200.250.58.156]:44817 "HELO perninha.conectiva.com.br") by vger.kernel.org with SMTP id ; Tue, 30 Jul 2002 17:27:51 -0400 Date: Tue, 30 Jul 2002 17:40:16 -0300 (BRT) From: Marcelo Tosatti X-X-Sender: marcelo@freak.distro.conectiva To: Andrew Morton Cc: lkml , Andrea Arcangeli Subject: Re: [patch] disable READA In-Reply-To: <3D47043E.413E9803@zip.com.au> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2055 Lines: 62 Who is using READA this days ? On Tue, 30 Jul 2002, Andrew Morton wrote: > > There's a bug in bread() which can cause it to misinterpret a > failed READA request as an IO error on SMP. > > If a filesytem block is subject to READA and __make_request() > decides that the request would block then __make_request() > will (via end_buffer_io_sync) mark the buffer as not uptodate > and will unlock it. > > But if another CPU attempts to bread() the same buffer at the same > time, the following happens: > > 1: ll_rw_block() sees the buffer is locked and does nothing at all > > 2: bread() does a wait_on_buffer() > > 3: the other CPU (the one doing READA) unlocks the non uptodate buffer > > 4: bread() sees the buffer come unlocked. It's not uptodate, so > bread() bogusly reports an IO error. > > I haven't seen it in the wild, because it is rare to get that > much read I/O in flight. reiserfs and ext3 (at least) use READA. > > An appropriate fix for 2.4 is to disable READA. > > > ll_rw_blk.c | 2 ++ > 1 files changed, 2 insertions > > --- 2.4.19-rc3/drivers/block/ll_rw_blk.c~no-readahead Tue Jul 30 14:18:17 2002 > +++ 2.4.19-rc3-akpm/drivers/block/ll_rw_blk.c Tue Jul 30 14:19:52 2002 > @@ -841,7 +841,9 @@ static int __make_request(request_queue_ > rw_ahead = 0; /* normal case; gets changed below for READA */ > switch (rw) { > case READA: > +#if 0 /* bread() misinterprets failed READA attempts as IO errors on SMP */ > rw_ahead = 1; > +#endif > rw = READ; /* drop into READ */ > case READ: > case WRITE: > > . > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/