bcache: do not subtract sectors_to_gc for bypassed IO

Since bypassed IOs use no bucket, so do not subtract sectors_to_gc to
trigger gc thread.
Signed-off-by: Ntang.junhui <tang.junhui@zte.com.cn>
Acked-by: NColy Li <colyli@suse.de>
Reviewed-by: NEric Wheeler <bcache@linux.ewheeler.net>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/md/bcache/request.c

@@ -196,12 +196,12 @@ static void bch_data_insert_start(struct closure *cl)
 	struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);
 	struct bio *bio = op->bio, *n;
 
-	if (atomic_sub_return(bio_sectors(bio), &op->c->sectors_to_gc) < 0)
-		wake_up_gc(op->c);
-
 	if (op->bypass)
 		return bch_data_invalidate(cl);
 
+	if (atomic_sub_return(bio_sectors(bio), &op->c->sectors_to_gc) < 0)
+		wake_up_gc(op->c);
+
 	/*
 	 * Journal writes are marked REQ_PREFLUSH; if the original write was a
 	 * flush, it'll wait on the journal write.