block: call bio_uninit in bio_endio

bio_free isn't a good place to free cgroup info. There are a
lot of cases bio is allocated in special way (for example, in stack) and
never gets called by bio_put hence bio_free, we are leaking memory. This
patch moves the free to bio endio, which should be called anyway. The
bio_uninit call in bio_free is kept, in case the bio never gets called
bio endio.

This assumes ->bi_end_io() doesn't access cgroup info, which seems true
in my audit.

This along with Christoph's integrity patch should fix the memory leak
issue.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -1833,6 +1833,8 @@ void bio_endio(struct bio *bio)
 	}
 
 	blk_throtl_bio_endio(bio);
+	/* release cgroup info */
+	bio_uninit(bio);
 	if (bio->bi_end_io)
 		bio->bi_end_io(bio);
 }