dm io: fix duplicate bio completion due to missing ref count

commit feb7695fe9fb83084aa29de0094774f4c9d4c9fc upstream.

If only a subset of the devices associated with multiple regions support
a given special operation (eg. DISCARD) then the dec_count() that is
used to set error for the region must increment the io->count.

Otherwise, when the dec_count() is called it can cause the dm-io
caller's bio to be completed multiple times.  As was reported against
the dm-mirror target that had mirror legs with a mix of discard
capabilities.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=196077
Reported-by: Zhang Yi <yizhan@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 0bf1a12..ee6045d 100644 (file)
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -302,6 +302,7 @@ static void do_region(int op, int op_flags, unsigned region,
                special_cmd_max_sectors = q->limits.max_write_same_sectors;
        if ((op == REQ_OP_DISCARD || op == REQ_OP_WRITE_SAME) &&
            special_cmd_max_sectors == 0) {
+               atomic_inc(&io->count);
                dec_count(io, region, -EOPNOTSUPP);
                return;
        }