Patch "dm io: fix duplicate bio completion due to missing ref count" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dm-io-fix-duplicate-bio-completion-due-to-missing-ref-count.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Mike Snitzer <[email protected]>
Date: Tue, 20 Jun 2017 19:14:30 -0400
Subject: dm io: fix duplicate bio completion due to missing ref count

From: Mike Snitzer <[email protected]>

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.

---
 drivers/md/dm-io.c |    1 +
 1 file changed, 1 insertion(+)

@@ -302,6 +302,7 @@ static void do_region(int op, int op_fla
 		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;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/dm-io-fix-duplicate-bio-completion-due-to-missing-ref-count.patch