md: sync sync_completed has correct value as recovery finishes.

[ Upstream commit 5ed1df2e ]

There can be a small window between the moment that recovery
actually writes the last block and the time when various sysfs
and /proc/mdstat attributes report that it has finished.
During this time, 'sync_completed' can have the wrong value.
This can confuse monitoring software.

So:
 - don't set curr_resync_completed beyond the end of the devices,
 - set it correctly when resync/recovery has completed.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

drivers/md/md.c

@@ -7409,6 +7409,9 @@ void md_do_sync(struct md_thread *thread)
 			break;
 
 		j += sectors;
+		if (j > max_sectors)
+			/* when skipping, extra large numbers can be returned. */
+			j = max_sectors;
 		if (j > 2)
 			mddev->curr_resync = j;
 		mddev->curr_mark_cnt = io_sectors;
@@ -7468,6 +7471,12 @@ void md_do_sync(struct md_thread *thread)
 	blk_finish_plug(&plug);
 	wait_event(mddev->recovery_wait, !atomic_read(&mddev->recovery_active));
 
+	if (!test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
+	    !test_bit(MD_RECOVERY_INTR, &mddev->recovery) &&
+	    mddev->curr_resync > 2) {
+		mddev->curr_resync_completed = mddev->curr_resync;
+		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
+	}
 	/* tell personality that we are finished */
 	mddev->pers->sync_request(mddev, max_sectors, &skipped, 1);