Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759778AbcDERoQ (ORCPT ); Tue, 5 Apr 2016 13:44:16 -0400 Received: from mail-pa0-f66.google.com ([209.85.220.66]:33553 "EHLO mail-pa0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758299AbcDERoO (ORCPT ); Tue, 5 Apr 2016 13:44:14 -0400 From: Ming Lei To: Jens Axboe , linux-kernel@vger.kernel.org Cc: linux-block@vger.kernel.org, kent.overstreet@gmail.com, Christoph Hellwig , Eric Wheeler , Sebastian Roesner , Ming Lei , stable@vger.kernel.org (4.2+), Shaohua Li Subject: [PATCH] block: make sure big bio is splitted into at most 256 bvecs Date: Wed, 6 Apr 2016 01:44:06 +0800 Message-Id: <1459878246-9249-1-git-send-email-ming.lei@canonical.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2442 Lines: 64 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+) 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