block: clear bio->bi_bdev when putting a bio back in the cache

This isn't strictly needed in terms of correctness, but it does allow
polling to know if the bio has been put already by a different task
and hence avoid polling something that we don't need to.

Cc: stable@vger.kernel.org
Fixes: be4d234d ("bio: add allocation cache abstraction")
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -772,6 +772,7 @@ static inline void bio_put_percpu_cache(struct bio *bio)
 
 	if ((bio->bi_opf & REQ_POLLED) && !WARN_ON_ONCE(in_interrupt())) {
 		bio->bi_next = cache->free_list;
+		bio->bi_bdev = NULL;
 		cache->free_list = bio;
 		cache->nr++;
 	} else {