block: blk_flush_integrity() for bio-based drivers

Since they lack requests to pin the request_queue active, synchronous
bio-based drivers may have in-flight integrity work from
bio_integrity_endio() that is not flushed by blk_freeze_queue().  Flush
that work to prevent races to free the queue and the final usage of the
blk_integrity profile.

This is temporary unless/until bio-based drivers start to generically
take a q_usage_counter reference while a bio is in-flight.

Cc: Martin K. Petersen <martin.petersen@oracle.com>
[martin: fix the CONFIG_BLK_DEV_INTEGRITY=n case]
Tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-core.c b/block/blk-core.c
index 9b4d735..6ebe33e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -561,6 +561,9 @@
 	queue_flag_set(QUEUE_FLAG_DEAD, q);
 	spin_unlock_irq(lock);
 
+	/* for synchronous bio-based driver finish in-flight integrity i/o */
+	blk_flush_integrity();
+
 	/* @q won't process any more request, flush async actions */
 	del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
 	blk_sync_queue(q);