From: Ted Ts'o Subject: Re: [PATCH -v2 6/6] ext4: use bio layer instead of buffer layer in mpage_da_submit_io Date: Mon, 25 Oct 2010 08:33:53 -0400 Message-ID: <20101025123353.GA16981@thunk.org> References: <1287866420-23762-1-git-send-email-tytso@mit.edu> <1287866420-23762-7-git-send-email-tytso@mit.edu> <87tykavom7.fsf@dmon-lap.sw.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, akpm@linux-foundation.org, axboe@kernel.dk To: Dmitry Return-path: Received: from thunk.org ([69.25.196.29]:50650 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753432Ab0JYMeH (ORCPT ); Mon, 25 Oct 2010 08:34:07 -0400 Content-Disposition: inline In-Reply-To: <87tykavom7.fsf@dmon-lap.sw.ru> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Oct 25, 2010 at 09:16:16AM +0400, Dmitry wrote: > > + if (bio) { > > + bio_get(io->io_bio); > > + submit_bio(io->io_op, io->io_bio); > > + BUG_ON(bio_flagged(io->io_bio, BIO_EOPNOTSUPP)); > Definitly this BUG_ON should be converted to ext4_error or something > similar, otherwhise writeback attempt to removed usb-stick will be fatal > for a whole system. IMHO it is reasonable to skip this check at all, > because all work will be done in ext4_end_bio() anyway. > > + bio_put(io->io_bio); Cut and pasted from XFS. From what I could tell from the block I/O layer, the only time the buffer I/O layer should return BIO_EOPNOTSUPP is if we pass it a discard or barrier request, and we're doing neither here. So I don't think it should trigger on a removed usb-stick. At the same time, it's not clear what good the BUG_ON() is doing here, either. So perhaps we could could drop the BUG_ON, at which point we could drop the bio_get() and bio_put() calls, too. To be honest I'm not entirely sure why the XFS code does this. Jens? Any reason why I shouldn't just remove the bio_get(), the BUG_ON()check, and bio_put() calls? - Ted