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Subject[PATCH 5.15 32/72] md/raid1: fix missing bitmap update w/o WriteMostly devices
Date
From: Song Liu <song@kernel.org>

commit 46669e8616c649c71c4cfcd712fd3d107e771380 upstream.

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@vger.kernel.org # v5.12+
Cc: Guoqing Jiang <guoqing.jiang@linux.dev>
Cc: Jens Axboe <axboe@kernel.dk>
Reported-by: Norbert Warmuth <nwarmuth@t-online.de>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/raid1.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1496,12 +1496,13 @@ static void raid1_write_request(struct m
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)) {

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