Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756647AbcDGX32 (ORCPT ); Thu, 7 Apr 2016 19:29:28 -0400 Received: from mx.ewheeler.net ([71.19.153.34]:52420 "EHLO mail.ewheeler.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752258AbcDGX3Z (ORCPT ); Thu, 7 Apr 2016 19:29:25 -0400 Date: Thu, 7 Apr 2016 23:29:07 +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 Content-Length: 5379 Lines: 148 On Thu, 7 Apr 2016, Ming Lei wrote: > On Thu, Apr 7, 2016 at 9:56 AM, Eric Wheeler wrote: > > 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? > > Can you see the issue with v4.1? > > You mentioned there are three reports: > > > [2014-02-04] https://bugzilla.redhat.com/show_bug.cgi?id=1061339 > > [2016-01-13] http://www.spinics.net/lists/linux-bcache/msg03335.html > https://bugzilla.kernel.org/show_bug.cgi?id=110771 > > [2016-03-25] http://thread.gmane.org/gmane.linux.kernel.bcache.devel/3607 [this thread] > https://bugzilla.kernel.org/show_bug.cgi?id=114871 > > The first one has been fixed by '8423ae3 block: Fix cloning of > discard/write same bios', as mentioned in bugzilla. > > The other two are reported on v4.4 and v4.5. > > If you look at the patch description, it is just needed for 4.3+. Oh, that could be---but just to be sure: I had thought perhaps this was an old issue since the first mention of this backtrace (but not bcache) was in 3.14 back in 2014 based on this post: https://bugzilla.redhat.com/show_bug.cgi?id=1061339 Is this relevant? -- Eric Wheeler > > Or I am wrong? > > > Thanks, > > > > > -- > > 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 > >> >