[PATCH 5.4 49/52] dm: interlock pending dm_io and dm_wait_for_bios_completion

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Mike Snitzer <snitzer@redhat.com>

commit 9f6dc633761006f974701d4c88da71ab68670749 upstream.

Commit d208b89401e0 ("dm: fix mempool NULL pointer race when
completing IO") didn't go far enough.

When bio_end_io_acct ends the count of in-flight I/Os may reach zero
and the DM device may be suspended. There is a possibility that the
suspend races with dm_stats_account_io.

Fix this by adding percpu "pending_io" counters to track outstanding
dm_io. Move kicking of suspend queue to dm_io_dec_pending(). Also,
rename md_in_flight_bios() to dm_in_flight_bios() and update it to
iterate all pending_io counters.

Fixes: d208b89401e0 ("dm: fix mempool NULL pointer race when completing IO")
Cc: stable@vger.kernel.org
Co-developed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/md/dm.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -681,14 +681,16 @@ static void end_io_acct(struct mapped_de
 {
 	unsigned long duration = jiffies - start_time;
 
-	generic_end_io_acct(md->queue, bio_op(bio), &dm_disk(md)->part0,
-			    start_time);
-
 	if (unlikely(dm_stats_used(&md->stats)))
 		dm_stats_account_io(&md->stats, bio_data_dir(bio),
 				    bio->bi_iter.bi_sector, bio_sectors(bio),
 				    true, duration, stats_aux);
 
+	smp_wmb();
+
+	generic_end_io_acct(md->queue, bio_op(bio), &dm_disk(md)->part0,
+			    start_time);
+
 	/* nudge anyone waiting on suspend queue */
 	if (unlikely(wq_has_sleeper(&md->wait)))
 		wake_up(&md->wait);
@@ -2494,6 +2496,8 @@ static int dm_wait_for_completion(struct
 	}
 	finish_wait(&md->wait, &wait);
 
+	smp_rmb();
+
 	return r;
 }