4.4-stable review patch. If anyone has any objections, please let me know.
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From: Andrea Righi andrea.righi@canonical.com
commit 3897b6f0a859288c22fb793fad11ec2327e60fcd 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
BugLink: https://bugs.launchpad.net/bugs/1812845 Fixes: 5a6ac9eacb49 ("Btrfs, raid56: support parity scrub on raid56") CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Johannes Thumshirn jthumshirn@suse.de Signed-off-by: Andrea Righi andrea.righi@canonical.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/raid56.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/btrfs/raid56.c +++ b/fs/btrfs/raid56.c @@ -2420,8 +2420,9 @@ static noinline void finish_parity_scrub bitmap_clear(rbio->dbitmap, pagenr, 1); kunmap(p);
- for (stripe = 0; stripe < rbio->real_stripes; stripe++) + for (stripe = 0; stripe < nr_data; stripe++) kunmap(page_in_rbio(rbio, stripe, pagenr, 0)); + kunmap(p_page); }
__free_page(p_page);