Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754088AbcDGCQP (ORCPT ); Wed, 6 Apr 2016 22:16:15 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:34075 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751925AbcDGCQO (ORCPT ); Wed, 6 Apr 2016 22:16:14 -0400 MIME-Version: 1.0 In-Reply-To: References: <1459878246-9249-1-git-send-email-ming.lei@canonical.com>

Date: Thu, 7 Apr 2016 10:16:10 +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: 4794 Lines: 129 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+. 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 >>