Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932499AbcDHAVZ (ORCPT ); Thu, 7 Apr 2016 20:21:25 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:45884 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932217AbcDHAVV (ORCPT ); Thu, 7 Apr 2016 20:21:21 -0400 MIME-Version: 1.0 In-Reply-To: References: <1459878246-9249-1-git-send-email-ming.lei@canonical.com>

Date: Fri, 8 Apr 2016 08:21:17 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] block: make sure big bio is splitted into at most 256 bvecs From: Ming Lei To: Eric Wheeler Cc: Jens Axboe , Linux Kernel Mailing List , linux-block@vger.kernel.org, Kent Overstreet , Christoph Hellwig , Sebastian Roesner , "4.2+" , Shaohua Li Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6092 Lines: 164 On Fri, Apr 8, 2016 at 7:29 AM, Eric Wheeler wrote: > 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, That is another bio_clone() issue, which was fixed by commit '8423ae3 block: Fix cloning of discard/write same bios'. If you did read the bugzillar comment and my reply, you should get the answer already. I am sorry for having to answer your same question again and again... > > -- > 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 >> >> >> > -- > 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