On Thu, Apr 7, 2016 at 9:36 AM, Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx> 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: [<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+) > > 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 Thanks, > >> 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html