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46669e8616
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 fd3b6975e9 ("md/raid1: only allocate write behind bio for WriteMostly device")
Fixes: fd3b6975e9 ("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.