From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760884AbcDFDqg (ORCPT ); Tue, 5 Apr 2016 23:46:36 -0400 Received: from mail-pf0-f193.google.com ([209.85.192.193]:33495 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760262AbcDFDqd (ORCPT ); Tue, 5 Apr 2016 23:46:33 -0400 Date: Tue, 5 Apr 2016 19:46:28 -0800 From: Kent Overstreet To: Ming Lei Cc: Jens Axboe , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, Christoph Hellwig , Eric Wheeler , Sebastian Roesner , "4.3+" , Shaohua Li Subject: Re: [PATCH v1] block: make sure big bio is splitted into at most 256 bvecs Message-ID: <20160406034628.GA25428@kmo-pixel> References: <1459914212-9330-1-git-send-email-ming.lei@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1459914212-9330-1-git-send-email-ming.lei@canonical.com> 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 On Wed, Apr 06, 2016 at 11:43:32AM +0800, Ming Lei wrote: > After arbitrary bio size is supported, the incoming bio may > be very big. We have to split the bio into small bios so that > each holds at most BIO_MAX_PAGES bvecs for safety reason, such > as bio_clone(). > > This patch fixes the following kernel crash: > > > [ 172.660142] BUG: unable to handle kernel NULL pointer dereference at 0000000000000028 > > [ 172.660229] IP: [] bio_trim+0xf/0x2a > > [ 172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0 > > [ 172.660399] Oops: 0000 [#1] SMP > > [...] > > [ 172.664780] Call Trace: > > [ 172.664813] [] ? raid1_make_request+0x2e8/0xad7 [raid1] > > [ 172.664846] [] ? blk_queue_split+0x377/0x3d4 > > [ 172.664880] [] ? md_make_request+0xf6/0x1e9 [md_mod] > > [ 172.664912] [] ? generic_make_request+0xb5/0x155 > > [ 172.664947] [] ? prio_io+0x85/0x95 [bcache] > > [ 172.664981] [] ? register_cache_set+0x355/0x8d0 [bcache] > > [ 172.665016] [] ? register_bcache+0x1006/0x1174 [bcache] > > Fixes: 54efd50(block: make generic_make_request handle arbitrarily sized bios) > Reported-by: Sebastian Roesner > Reported-by: Eric Wheeler > Cc: stable@vger.kernel.org (4.3+) > Cc: Shaohua Li > Cc: Kent Overstreet > Signed-off-by: Ming Lei That'll work Acked-by: Kent Overstreet > --- > V1: > - Kent pointed out that using max io size can't cover > the case of non-full bvecs/pages > > The issue can be reproduced by the following approach: > - create one raid1 over two virtio-blk > - build bcache device over the above raid1 and another cache device > and bucket size is set 2Mbytes > - set cache mode as writeback > - run random write over ext4 on the bcache device > - then the crash can be triggered > > block/blk-merge.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index 2613531..7b96471 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -94,8 +94,10 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, > bool do_split = true; > struct bio *new = NULL; > const unsigned max_sectors = get_max_io_size(q, bio); > + unsigned bvecs = 0; > > bio_for_each_segment(bv, bio, iter) { > + bvecs++; > /* > * If the queue doesn't support SG gaps and adding this > * offset would create a gap, disallow it. > @@ -103,6 +105,23 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, > if (bvprvp && bvec_gap_to_prev(q, bvprvp, bv.bv_offset)) > goto split; > > + /* > + * With arbitrary bio size, the incoming bio may be very > + * big. We have to split the bio into small bios so that > + * each holds at most BIO_MAX_PAGES bvecs because > + * bio_clone() can fail to allocate big bvecs. > + * > + * It should have been better to apply the limit per > + * request queue in which bio_clone() is involved, > + * instead of globally. The biggest blocker is > + * bio_clone() in bio bounce. > + * > + * TODO: deal with bio bounce's bio_clone() gracefully > + * and convert the global limit into per-queue limit. > + */ > + if (bvecs >= BIO_MAX_PAGES) > + goto split; > + > if (sectors + (bv.bv_len >> 9) > max_sectors) { > /* > * Consider this a new segment if we're splitting in > -- > 1.9.1 >