On Tue, Apr 05, 2016 at 11:27:21AM -0700, Shaohua Li wrote: > On Wed, Apr 06, 2016 at 01:44:06AM +0800, 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) > > this bug is introduced by d2be537c3ba > > 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 > > can you explain why this is better than my original patch? Shaohua, what was your original patch? I'm sorry, I know I saw it at one point but I can't remember what it was. I didn't see Jeff's patch that introduced this bug until your email just now. Argh. Jeff, "block: bump BLK_DEF_MAX_SECTORS to 2560" doesn't make much sense as far as I can tell without changing the BIO_MAX_PAGES too - that's probably why you weren't seeing much performance increase from that patch... But BLK_DEF_MAX_SECTORS should not have been enforcing the BIO_MAX_PAGES limit so that patch was not at fault. -- 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