On 06/10/2016 01:07 PM, 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] > > 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 <[email protected]> > Reported-by: Eric Wheeler <[email protected]> > Cc: [email protected] (4.3+) > Cc: Shaohua Li <[email protected]> > Acked-by: Kent Overstreet <[email protected]> > Signed-off-by: Ming Lei <[email protected]> > --- > V2: > - don't mark as REQ_NOMERGE in case the bio is splitted > for reaching the limit of bvecs count > V1: > - Kent pointed out that using max io size can't cover > the case of non-full bvecs/pages > block/blk-merge.c | 35 ++++++++++++++++++++++++++++++++--- > 1 file changed, 32 insertions(+), 3 deletions(-) > Hmm. So everybody is suffering because someone _might_ be using bio_clone? Why can't we fixup bio_clone() (or the callers of which) to correctly set the queue limits?
Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking [email protected] +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg)
