On 1/4/22 7:04 AM, Song Liu wrote:
commit [1] causes missing bitmap updates when there isn't any WriteMostly devices. Detailed steps to reproduce by Norbert (which somehow didn't make to lore): # setup md10 (raid1) with two drives (1 GByte sparse files) dd if=/dev/zero of=disk1 bs=1024k seek=1024 count=0 dd if=/dev/zero of=disk2 bs=1024k seek=1024 count=0 losetup /dev/loop11 disk1 losetup /dev/loop12 disk2 mdadm --create /dev/md10 --level=1 --raid-devices=2 /dev/loop11 /dev/loop12 # add bitmap (aka write-intent log) mdadm /dev/md10 --grow --bitmap=internal echo check > /sys/block/md10/md/sync_action root:# cat /sys/block/md10/md/mismatch_cnt 0 root:# # remove member drive disk2 (loop12) mdadm /dev/md10 -f loop12 ; mdadm /dev/md10 -r loop12 # modify degraded md device dd if=/dev/urandom of=/dev/md10 bs=512 count=1 # no blocks recorded as out of sync on the remaining member disk1/loop11 root:# mdadm -X /dev/loop11 | grep Bitmap Bitmap : 16 bits (chunks), 0 dirty (0.0%) root:# # re-add disk2, nothing synced because of empty bitmap mdadm /dev/md10 --re-add /dev/loop12 # check integrity again echo check > /sys/block/md10/md/sync_action # disk1 and disk2 are no longer in sync, reads return differend data root:# cat /sys/block/md10/md/mismatch_cnt 128 root:# # clean up mdadm -S /dev/md10 losetup -d /dev/loop11 losetup -d /dev/loop12 rm disk1 disk2 Fix this by moving the WriteMostly check to the if condition for alloc_behind_master_bio(). [1] commit fd3b6975e9c1 ("md/raid1: only allocate write behind bio for WriteMostly device") Fixes: fd3b6975e9c1 ("md/raid1: only allocate write behind bio for WriteMostly device") Cc: stable@xxxxxxxxxxxxxxx # v5.12+ Cc: Guoqing Jiang <guoqing.jiang@xxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Reported-by: Norbert Warmuth <nwarmuth@xxxxxxxxxxx> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Song Liu <song@xxxxxxxxxx> --- drivers/md/raid1.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index 7dc8026cf6ee..85505424f7a4 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -1496,12 +1496,13 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio, if (!r1_bio->bios[i]) continue;- if (first_clone && test_bit(WriteMostly, &rdev->flags)) {+ if (first_clone) { /* do behind I/O ? * Not if there are too many, or cannot * allocate memory, or a reader on WriteMostly * is waiting for behind writes to flush */ if (bitmap && + test_bit(WriteMostly, &rdev->flags) && (atomic_read(&bitmap->behind_writes) < mddev->bitmap_info.max_write_behind) && !waitqueue_active(&bitmap->behind_wait)) {
Indeed, I missed that md_bitmap_startwrite should be always called for the first clone.
Thanks, Guoqing
