md/raid1: fix data lost for writemostly rdev

JIRA: https://issues.redhat.com/browse/RHEL-94433

commit 93dec51
Author: Yu Kuai <yukuai3@huawei.com>
Date:   Wed Sep 3 09:41:40 2025 +0800

    md/raid1: fix data lost for writemostly rdev

    If writemostly is enabled, alloc_behind_master_bio() will allocate a new
    bio for rdev, with bi_opf set to 0. Later, raid1_write_request() will
    clone from this bio, hence bi_opf is still 0 for the cloned bio. Submit
    this cloned bio will end up to be read, causing write data lost.

    Fix this problem by inheriting bi_opf from original bio for
    behind_mast_bio.

    Fixes: e879a0d ("md/raid1,raid10: don't ignore IO flags")
    Reported-and-tested-by: Ian Dall <ian@beware.dropbear.id.au>
    Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220507
    Link: https://lore.kernel.org/linux-raid/20250903014140.3690499-1-yukuai1@huaweicloud.com
    Signed-off-by: Yu Kuai <yukuai3@huawei.com>
    Reviewed-by: Li Nan <linan122@huawei.com>

Signed-off-by: Nigel Croxon <ncroxon@redhat.com>

Author: ncroxon

drivers/md/raid1.c

@@ -1225,7 +1225,7 @@ static void alloc_behind_master_bio(struct r1bio *r1_bio,
 	int i = 0;
 	struct bio *behind_bio = NULL;
 
-	behind_bio = bio_alloc_bioset(NULL, vcnt, 0, GFP_NOIO,
+	behind_bio = bio_alloc_bioset(NULL, vcnt, bio->bi_opf, GFP_NOIO,
 				      &r1_bio->mddev->bio_set);
 
 	/* discard op, we don't support writezero/writesame yet */