dm stats: fix too short end duration_ns when using precise_timestamps

dm_stats_account_io()'s STAT_PRECISE_TIMESTAMPS support doesn't handle
the fact that with commit b879f915bc48 ("dm: properly fix redundant
bio-based IO accounting") io->start_time _may_ be in the past (meaning
the start_io_acct() was deferred until later).

Add a new dm_stats_recalc_precise_timestamps() helper that will
set/clear a new 'precise_timestamps' flag in the dm_stats struct based
on whether any configured stats enable STAT_PRECISE_TIMESTAMPS.
And update DM core's alloc_io() to use dm_stats_record_start() to set
stats_aux.duration_ns if stats->precise_timestamps is true.

Also, remove unused 'last_sector' and 'last_rw' members from the
dm_stats struct.

Fixes: b879f915bc48 ("dm: properly fix redundant bio-based IO accounting")
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>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index c72a271ea999..3ae76900023b 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -552,6 +552,8 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
 
 	io->start_time = jiffies;
 
+	dm_stats_record_start(&md->stats, &io->stats_aux);
+
 	return io;
 }