On Tue, Apr 05, 2016 at 04:27:33PM -0800, Kent Overstreet wrote: > 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-kernel...@roesner-online.de> > > > Reported-by: Eric Wheeler <bca...@lists.ewheeler.net> > > > Cc: sta...@vger.kernel.org (4.2+) > > > Cc: Shaohua Li <s...@fb.com> > > > Signed-off-by: Ming Lei <ming....@canonical.com> > > > --- > > > 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.
this one: http://marc.info/?l=linux-kernel&m=145926976808760&w=2
