[dm-devel] [PATCH v5.10] dm: interlock pending dm_io and dm_wait_for_bios_completion

[Mikulas Patocka]

This is backport of the patch 9f6dc6337610 ("dm: interlock pending dm_io
and dm_wait_for_bios_completion") for the kernel 5.10.

The bugs fixed by this patch can cause random crashing when reloading dm
table, so it is eligible for stable backport.

Note that the percpu variable md->pending_io is not needed in the stable
kernels, because the "in_flight" counter in struct disk_stats counts the
same value, so it is not backported. In order to fix this bug, we swap the
calls to bio_end_io_acct and dm_stats_account_io.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Reviewed-by: Mike Snitzer <snitzer at kernel.org>

---
 drivers/md/dm.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux-stable/drivers/md/dm.c
===================================================================
--- linux-stable.orig/drivers/md/dm.c	2022-04-30 20:09:28.000000000 +0200
+++ linux-stable/drivers/md/dm.c	2022-04-30 20:10:19.000000000 +0200
@@ -612,13 +612,15 @@ static void end_io_acct(struct mapped_de
 {
 	unsigned long duration = jiffies - start_time;
 
-	bio_end_io_acct(bio, 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();
+
+	bio_end_io_acct(bio, start_time);
+
 	/* nudge anyone waiting on suspend queue */
 	if (unlikely(wq_has_sleeper(&md->wait)))
 		wake_up(&md->wait);
@@ -2348,6 +2350,8 @@ static int dm_wait_for_bios_completion(s
 	}
 	finish_wait(&md->wait, &wait);
 
+	smp_rmb();
+
 	return r;
 }