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: [<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] Fixes: 54efd50(block: make generic_make_request handle arbitrarily sized bios) Reported-by: Sebastian Roesner <sroesner-kernelorg@xxxxxxxxxxxxxxxxx> Reported-by: Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx (4.2+) Cc: Shaohua Li <shli@xxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx> --- 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
