Commit 2b95e85f authored by Andrea Righi's avatar Andrea Righi Committed by Greg Kroah-Hartman

btrfs: raid56: properly unmap parity page in finish_parity_scrub()

commit 3897b6f0 upstream.

Parity page is incorrectly unmapped in finish_parity_scrub(), triggering
a reference counter bug on i386, i.e.:

 [ 157.662401] kernel BUG at mm/highmem.c:349!
 [ 157.666725] invalid opcode: 0000 [#1] SMP PTI

The reason is that kunmap(p_page) was completely left out, so we never
did an unmap for the p_page and the loop unmapping the rbio page was
iterating over the wrong number of stripes: unmapping should be done
with nr_data instead of rbio->real_stripes.

Test case to reproduce the bug:

 - create a raid5 btrfs filesystem:
   # mkfs.btrfs -m raid5 -d raid5 /dev/sdb /dev/sdc /dev/sdd /dev/sde

 - mount it:
   # mount /dev/sdb /mnt

 - run btrfs scrub in a loop:
   # while :; do btrfs scrub start -BR /mnt; done

Fixes: 5a6ac9ea ("Btrfs, raid56: support parity scrub on raid56")
CC: # 4.4+
Reviewed-by: default avatarJohannes Thumshirn <>
Signed-off-by: default avatarAndrea Righi <>
Reviewed-by: default avatarDavid Sterba <>
Signed-off-by: default avatarDavid Sterba <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent da04627d
......@@ -2414,8 +2414,9 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
bitmap_clear(rbio->dbitmap, pagenr, 1);
for (stripe = 0; stripe < rbio->real_stripes; stripe++)
for (stripe = 0; stripe < nr_data; stripe++)
kunmap(page_in_rbio(rbio, stripe, pagenr, 0));
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