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block: make sure a big bio is split into at most 256 bvecs 

After arbitrary bio size was introduced, 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: [<ffffffff811e53b4>] bio_trim+0xf/0x2a
> [  172.660289] PGD 7faf3e067 PUD 7f9279067 PMD 0
> [  172.660399] Oops: 0000 [#1] SMP
> [...]
> [  172.664780] Call Trace:
> [  172.664813]  [<ffffffffa007f3be>] ? raid1_make_request+0x2e8/0xad7 [raid1]
> [  172.664846]  [<ffffffff811f07da>] ? blk_queue_split+0x377/0x3d4
> [  172.664880]  [<ffffffffa005fb5f>] ? md_make_request+0xf6/0x1e9 [md_mod]
> [  172.664912]  [<ffffffff811eb860>] ? generic_make_request+0xb5/0x155
> [  172.664947]  [<ffffffffa0445c89>] ? prio_io+0x85/0x95 [bcache]
> [  172.664981]  [<ffffffffa0448252>] ? register_cache_set+0x355/0x8d0 [bcache]
> [  172.665016]  [<ffffffffa04497d3>] ? register_bcache+0x1006/0x1174 [bcache]

The issue can be reproduced by the following steps:
	- create one raid1 over two virtio-blk
	- build bcache device over the above raid1 and another cache device
	and bucket size is set as 2Mbytes
	- set cache mode as writeback
	- run random write over ext4 on the bcache device

Fixes: 54efd50(block: make generic_make_request handle arbitrarily sized bios)
Reported-by: Sebastian Roesner <sroesner-kernelorg@roesner-online.de>
Reported-by: Eric Wheeler <bcache@lists.ewheeler.net>
Cc: stable@vger.kernel.org (4.3+)
Cc: Shaohua Li <shli@fb.com>
Acked-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Ming Lei 2016-08-23 21:49:45 +08:00 committed by Jens Axboe
parent 9b47f77a68
commit 4d70dca4ea
1 changed files with 22 additions and 0 deletions
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22
block/blk-merge.c
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@ -94,8 +94,30 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
bool do_split = true; bool do_split = true;
struct bio *new = NULL; struct bio *new = NULL;
const unsigned max_sectors = get_max_io_size(q, bio); const unsigned max_sectors = get_max_io_size(q, bio);
unsigned bvecs = 0;
bio_for_each_segment(bv, bio, iter) { bio_for_each_segment(bv, bio, iter) {
/*
* 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 because
* bio_clone() can fail to allocate big bvecs.
*
* It should have been better to apply the limit per
* request queue in which bio_clone() is involved,
* instead of globally. The biggest blocker is the
* bio_clone() in bio bounce.
*
* If bio is splitted by this reason, we should have
* allowed to continue bios merging, but don't do
* that now for making the change simple.
*
* TODO: deal with bio bounce's bio_clone() gracefully
* and convert the global limit into per-queue limit.
*/
if (bvecs++ >= BIO_MAX_PAGES)
goto split;
/* /*
* If the queue doesn't support SG gaps and adding this * If the queue doesn't support SG gaps and adding this
* offset would create a gap, disallow it. * offset would create a gap, disallow it.