[PATCH v4] rbd: fix the memory leak of bio_chain_clone

[Guangliang Zhao <gzhao@suse.com>]

The bio_pair alloced in bio_chain_clone would not be freed,
this will cause a memory leak. It could be freed actually only
after 3 times release, because the reference count of bio_pair
is initialized to 3 when bio_split and bio_pair_release only
drops the reference count.

The function bio_pair_release must be called three times for
releasing bio_pair, and the callback functions of bios on the
requests will be called when the last release time in bio_pair_release,
however, these functions will also be called in rbd_req_cb. In
other words, they will be called twice, and it may cause serious
consequences.

This patch clones bio chain from the origin directly instead of
bio_split. The new bio chain can be released whenever we don't
need it.

This patch can just handle the split of *single page* bios, but
it's enough here for the following reasons:

Only bios span across multiple osds need to be split, and these bios
*must* be single page because of rbd_merge_bvec. With the function,
the new bvec will not permitted to merge, if it make the bio cross
the osd boundary, except it is the first one. In other words, there
are two types of bio:

	- the bios don't cross the osd boundary
	  They have one or more pages. The value of offset will
	  always be 0 in this case, so nothing will be changed, and
	  the code changes tmp bios doesn't take effact at all.

	- the bios cross the osd boundary
	  Each one have only one page. These bios need to be split,
	  and the offset is used to indicate the next bio, it makes
	  sense only in this instance.

Signed-off-by: Guangliang Zhao <gzhao@suse.com>
---
 drivers/block/rbd.c |   73 +++++++++++++++++++++-----------------------------
 1 files changed, 31 insertions(+), 42 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 013c7a5..356657d 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -712,51 +712,46 @@ static void zero_bio_chain(struct bio *chain, int start_ofs)
 	}
 }
 
-/*
- * bio_chain_clone - clone a chain of bios up to a certain length.
- * might return a bio_pair that will need to be released.
+/**
+ *      bio_chain_clone - clone a chain of bios up to a certain length.
+ *      @old: bio to clone
+ *      @offset: start point for bio clone
+ *      @len: length of bio chain
+ *      @gfp_mask: allocation priority
+ *
+ *      RETURNS:
+ *      Pointer to new bio chain on success, NULL on failure.
  */
-static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
-				   struct bio_pair **bp,
+static struct bio *bio_chain_clone(struct bio **old, int *offset,
 				   int len, gfp_t gfpmask)
 {
 	struct bio *tmp, *old_chain = *old, *new_chain = NULL, *tail = NULL;
 	int total = 0;
 
-	if (*bp) {
-		bio_pair_release(*bp);
-		*bp = NULL;
-	}
-
 	while (old_chain && (total < len)) {
+		int need = len - total;
+
 		tmp = bio_kmalloc(gfpmask, old_chain->bi_max_vecs);
 		if (!tmp)
 			goto err_out;
 
-		if (total + old_chain->bi_size > len) {
-			struct bio_pair *bp;
-
-			/*
-			 * this split can only happen with a single paged bio,
-			 * split_bio will BUG_ON if this is not the case
-			 */
-			dout("bio_chain_clone split! total=%d remaining=%d"
-			     "bi_size=%d\n",
-			     (int)total, (int)len-total,
-			     (int)old_chain->bi_size);
-
-			/* split the bio. We'll release it either in the next
-			   call, or it will have to be released outside */
-			bp = bio_split(old_chain, (len - total) / SECTOR_SIZE);
-			if (!bp)
-				goto err_out;
-
-			__bio_clone(tmp, &bp->bio1);
-
-			*next = &bp->bio2;
+		__bio_clone(tmp, old_chain);
+		tmp->bi_sector += *offset >> SECTOR_SHIFT;
+		tmp->bi_io_vec->bv_offset += *offset >> SECTOR_SHIFT;
+		/*
+		 * The bios span across multiple osd objects must be
+		 * single paged, rbd_merge_bvec would guarantee it.
+		 * So we needn't worry about other things.
+		 */
+		if (tmp->bi_size - *offset > need) {
+			tmp->bi_size = need;
+			tmp->bi_io_vec->bv_len = need;
+			*offset += need;
 		} else {
-			__bio_clone(tmp, old_chain);
-			*next = old_chain->bi_next;
+			old_chain = old_chain->bi_next;
+			tmp->bi_size -= *offset;
+			tmp->bi_io_vec->bv_len -= *offset;
+			*offset = 0;
 		}
 
 		tmp->bi_bdev = NULL;
@@ -769,7 +764,6 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
 			tail->bi_next = tmp;
 			tail = tmp;
 		}
-		old_chain = old_chain->bi_next;
 
 		total += tmp->bi_size;
 	}
@@ -1447,13 +1441,12 @@ static void rbd_rq_fn(struct request_queue *q)
 {
 	struct rbd_device *rbd_dev = q->queuedata;
 	struct request *rq;
-	struct bio_pair *bp = NULL;
 
 	while ((rq = blk_fetch_request(q))) {
 		struct bio *bio;
-		struct bio *rq_bio, *next_bio = NULL;
+		struct bio *rq_bio;
 		bool do_write;
-		int size, op_size = 0;
+		int size, op_size = 0, offset = 0;
 		u64 ofs;
 		int num_segs, cur_seg = 0;
 		struct rbd_req_coll *coll;
@@ -1503,7 +1496,7 @@ static void rbd_rq_fn(struct request_queue *q)
 						  ofs, size,
 						  NULL, NULL);
 			kref_get(&coll->kref);
-			bio = bio_chain_clone(&rq_bio, &next_bio, &bp,
+			bio = bio_chain_clone(&rq_bio, &offset,
 					      op_size, GFP_ATOMIC);
 			if (!bio) {
 				rbd_coll_end_req_index(rq, coll, cur_seg,
@@ -1531,12 +1524,8 @@ next_seg:
 			ofs += op_size;
 
 			cur_seg++;
-			rq_bio = next_bio;
 		} while (size > 0);
 		kref_put(&coll->kref, rbd_coll_release);
-
-		if (bp)
-			bio_pair_release(bp);
 		spin_lock_irq(q->queue_lock);
 	}
 }
-- 
1.7.3.4