From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264537AbUAARc2 (ORCPT ); Thu, 1 Jan 2004 12:32:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264539AbUAARc2 (ORCPT ); Thu, 1 Jan 2004 12:32:28 -0500 Received: from websrv.werbeagentur-aufwind.de ([213.239.197.241]:13991 "EHLO mail.werbeagentur-aufwind.de") by vger.kernel.org with ESMTP id S264537AbUAARcS (ORCPT ); Thu, 1 Jan 2004 12:32:18 -0500 Date: Thu, 1 Jan 2004 18:32:14 +0100 From: Christophe Saout To: Linux-Kernel Mailing List Cc: Jens Axboe , Andrew Morton Subject: [RFC][PATCH] Move bv_offset/bv_len update after bio_endio in __end_that_request_first Message-ID: <20040101173214.GA4496@leto.cs.pocnet.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.5.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! Can we move the update of bio_index(bio)->bv_offset and bv_len after the bio_endio call in __end_that_request_first please (if a bvec is partially completed)? The bi_idx is currently also updated after the bio_endio call. Currently the bi_end_io function cannot exactly determine whether a bvec was completed or not. Think of the following situation: bv_offset is 0 and bv_len is 4096, now the driver completes 2048 bytes of that bvec. At the moment bv_offset and bv_len are set to 2048 first. The bi_end_io function can't distinguish between this situation and the situation where bv_offset and bv_len were 2048 before and that bvec was completed (because bi_idx is incremented afterwards). This shouldn't break any user since most users are waiting for the whole bio to complete with if (bio->bi_size > 0) return 1;. I need this because I want to release buffers as soon as possible. The incoming bio can get split by my driver due to problems allocating buffers. If the partial bio returns and can't release its buffers immediately the whole thing might deadlock. That's why I need to know exactly how many and which bvecs were completed in my bi_end_io function. Or do you think it is safer to count backwards using bi_vcnt and bi_size? diff -Nur linux-2.6.0.orig/drivers/block/ll_rw_blk.c linux-2.6.0/drivers/block/ll_rw_blk.c --- linux-2.6.0.orig/drivers/block/ll_rw_blk.c 2003-11-24 02:31:11.000000000 +0100 +++ linux-2.6.0/drivers/block/ll_rw_blk.c 2004-01-01 14:27:34.222352384 +0100 @@ -2494,8 +2494,6 @@ * not a complete bvec done */ if (unlikely(nbytes > nr_bytes)) { - bio_iovec_idx(bio, idx)->bv_offset += nr_bytes; - bio_iovec_idx(bio, idx)->bv_len -= nr_bytes; bio_nbytes += nr_bytes; total_bytes += nr_bytes; break; @@ -2531,7 +2529,9 @@ */ if (bio_nbytes) { bio_endio(bio, bio_nbytes, error); - req->bio->bi_idx += next_idx; + bio->bi_idx += next_idx; + bio_iovec(bio)->bv_offset += nr_bytes; + bio_iovec(bio)->bv_len -= nr_bytes; } blk_recalc_rq_sectors(req, total_bytes >> 9);