From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754239AbcDGB41 (ORCPT ); Wed, 6 Apr 2016 21:56:27 -0400 Received: from mx.ewheeler.net ([71.19.153.34]:47109 "EHLO mail.ewheeler.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752346AbcDGB4Z (ORCPT ); Wed, 6 Apr 2016 21:56:25 -0400 Date: Thu, 7 Apr 2016 01:56:19 +0000 (UTC) From: Eric Wheeler X-X-Sender: lists@mail.ewheeler.net To: Ming Lei cc: Jens Axboe , Linux Kernel Mailing List , linux-block@vger.kernel.org, Kent Overstreet , Christoph Hellwig , Sebastian Roesner , "4.2+" , Shaohua Li Subject: Re: [PATCH] block: make sure big bio is splitted into at most 256 bvecs In-Reply-To: Message-ID: References: <1459878246-9249-1-git-send-email-ming.lei@canonical.com> User-Agent: Alpine 2.11 (LRH 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 7 Apr 2016, Ming Lei wrote: > On Thu, Apr 7, 2016 at 9:36 AM, Eric Wheeler wrote: > > On Wed, 6 Apr 2016, 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 (4.2+) > > > > Ming Lei, > > > > get_max_io_size doesn't appear until 4.5 based on a quick LXR check so we > > won't see it in stable I don't think. > > > > It would be nice to see this fixed in 4.1 (if affected there). Is there > > The issue should be introduced to v4.3 via 54efd50 > > > another place this could be applied to be a bit more backward compatible? > > The v1 needn't change to get_max_io_size(), and it should be simple enough > to backport to previous stables, please try it: > > http://marc.info/?l=linux-block&m=145991422422927&w=2 V1 changes blk_bio_segment_split() which doesn't exist until 4.3. How might you port this to v4.1.y? -- Eric Wheeler > > Thanks, > > > > >> Cc: Shaohua Li > >> Signed-off-by: Ming Lei > >> --- > >> I can reproduce the issue and verify the fix by the following approach: > >> - create one raid1 over two virtio-blk > >> - build bcache device over the above raid1 and another cache device. > >> - set cache mode as writeback > >> - run random write over ext4 on the bcache device > >> - then the crash can be triggered > >> > >> block/blk-merge.c | 12 ++++++++++++ > >> 1 file changed, 12 insertions(+) > >> > >> diff --git a/block/blk-merge.c b/block/blk-merge.c > >> index 2613531..9a8651f 100644 > >> --- a/block/blk-merge.c > >> +++ b/block/blk-merge.c > >> @@ -79,6 +79,18 @@ static inline unsigned get_max_io_size(struct request_queue *q, > >> /* aligned to logical block size */ > >> sectors &= ~(mask >> 9); > >> > >> + /* > >> + * 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 for safety reason, such as > >> + * bio_clone(). > >> + * > >> + * In the future, the limit might be converted into per-queue > >> + * flag. > >> + */ > >> + sectors = min_t(unsigned, sectors, BIO_MAX_PAGES << > >> + (PAGE_CACHE_SHIFT - 9)); > >> + > >> return sectors; > >> } > >> > >> -- > >> 1.9.1 > >> > >> > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-block" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html >