Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752841AbcCLOgW (ORCPT ); Sat, 12 Mar 2016 09:36:22 -0500 Received: from mail-pf0-f173.google.com ([209.85.192.173]:33329 "EHLO mail-pf0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750998AbcCLOgR (ORCPT ); Sat, 12 Mar 2016 09:36:17 -0500 Date: Sat, 12 Mar 2016 05:36:12 -0900 From: Kent Overstreet To: Ming Lei Cc: Ming Lin , Jens Axboe , Linux Kernel Mailing List , torvalds@linux-foundation.org Subject: Re: e827091cb1 "block: merge: get the 1st and last bvec via helpers" broken Message-ID: <20160312143612.GA30418@kmo-pixel> References: <20160312074329.GA19066@kmo-pixel> <20160312092421.GA20839@kmo-pixel> <20160312121236.GA25403@kmo-pixel> <20160312134843.GA27821@kmo-pixel> <20160312140256.GA29313@kmo-pixel> <20160312222548.6a81d13b@tom-T450> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160312222548.6a81d13b@tom-T450> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1659 Lines: 48 On Sat, Mar 12, 2016 at 10:25:48PM +0800, Ming Lei wrote: > On Sat, 12 Mar 2016 05:02:56 -0900 > Kent Overstreet wrote: > > > Here's the output of the patch below: > > > > generic/036 11s ...run fstests generic/036 at 2016-03-12 13:58:21 > > end 4096 0 ffffea0001d611c0 end2 1024 0 ffffea0001d611c0 > > len 1024 offset 0 page ffffea0001d611c0 > > KGDB: Waiting for remote debugger > > > > Your code gives a biovec with bv_len of 4096, the old code gives a biovec with > > bv_len of 1024 (and then we dump every biovec, we see that the bio had only a > > single biovec that did indeed have bv_len == 1024). > > I guess we shouldn't have optimized for the case of non-cloned bio, could you > try the following patch? > > -- > diff --git a/include/linux/bio.h b/include/linux/bio.h > index 1e7248f..4abc129 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -267,11 +267,6 @@ static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv) > struct bvec_iter iter = bio->bi_iter; > int idx; > > - if (!bio_flagged(bio, BIO_CLONED)) { > - *bv = bio->bi_io_vec[bio->bi_vcnt - 1]; > - return; > - } > - > if (unlikely(!bio_multiple_segments(bio))) { > *bv = bio_iovec(bio); > return; > > Thanks, > Ming Yes, that's it. !BIO_CLONED is _not_ a guarantee that bi_size doesn't straddle the middle of a bvec - bcachefs was hitting this by bouncing a bio that had already been split (which can happen elsewhere in the kernel...) but there's other (perfectly legal) ways it can happen. I would still strongly suggest reverting the patch for 4.5 and resubmitting during the next merge window.