On Wed, 1 Jun 2016, James Johnston wrote: > Hi Mikulas, > > > bio_alloc can allocate a bio with at most BIO_MAX_PAGES (256) vector > > entries. However, the incoming bio may have more vector entries if it was > > allocated by other means. For example, bcache submits bios with more than > > BIO_MAX_PAGES entries. This results in bio_alloc failure. > > > > To avoid the failure, change the code so that it allocates bio with at > > most BIO_MAX_PAGES entries. If the incoming bio has more entries, > > bio_add_page will fail and a new bio will be allocated - the code that > > handles bio_add_page failure already exists in the dm-log-writes target. > > > > Also, move atomic_inc(&lc->io_blocks) before bio_alloc to fix a bug that > > the target hangs if bio_alloc fails. The error path does put_io_block(lc), > > so we must do atomic_inc(&lc->io_blocks) before invoking the error path to > > avoid underflow of lc->io_blocks. > > > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx # v4.1+ > > How does this relate to the previous patch you made to dm-crypt? How best > should I test this? It looks like the dm-crypt patch fixed the problem. > > Should I test by applying this patch ONLY and reverting the dm-crypt patch? > (i.e. does this patch also fix the problem.) Or should I just test with > both patches applied simultaneously? > > James When I found a bug in dm-crypt, I searched the other targets for the same problem and found out that the same bug is also present in dm-log-writes. The bug in dm-log-writes can be reproduced if you make a bcache device with 2MiB bucket size and place in on the dm-log-writes target. When the bug is present, the dm-log-writes target reports "device-mapper: log-writes: Couldn't alloc log bio". This is a script that triggers the bug for dm-log-writes. Before running the script, create devices /dev/mapper/loop-test1, loop-test2 and loop-test3. Mikulas wipefs -a /dev/mapper/loop-test1 ./make-bcache --wipe-bcache --bucket 2M -C /dev/mapper/loop-test1 dmsetup create backCrypt --table "0 `blockdev --getsize /dev/mapper/loop-test2` log-writes /dev/mapper/loop-test2 /dev/mapper/loop-test3" wipefs -a /dev/mapper/backCrypt ./make-bcache --wipe-bcache -B /dev/mapper/backCrypt modprobe bcache echo /dev/mapper/loop-test1 > /sys/fs/bcache/register echo /dev/mapper/backCrypt > /sys/fs/bcache/register ./bcache-super-show /dev/mapper/loop-test1 | grep cset.uuid | cut -f 3 >/sys/block/bcache0/bcache/attach echo writeback > /sys/block/bcache0/bcache/cache_mode cd /sys/block/bcache0/bcache echo 0 > sequential_cutoff # Verify that the cache is attached (i.e. does not say "no cache") cat state dd if=/dev/urandom of=/dev/bcache0 bs=1M count=250 cat dirty_data cat state echo 1 > detach cat dirty_data cat state -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
