block: bfq: swap puts in bfqg_and_blkg_put

commit d5274b3c upstream.

Fix trivial use-after-free. This could be last reference to bfqg.

Fixes: 8f9bebc3 ("block, bfq: access and cache blkg data only when safe")
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

block/bfq-cgroup.c

@@ -224,9 +224,9 @@ static void bfqg_and_blkg_get(struct bfq_group *bfqg)
 
 void bfqg_and_blkg_put(struct bfq_group *bfqg)
 {
-	bfqg_put(bfqg);
-
 	blkg_put(bfqg_to_blkg(bfqg));
+
+	bfqg_put(bfqg);
 }
 
 void bfqg_stats_update_io_add(struct bfq_group *bfqg, struct bfq_queue *bfqq,