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 old bios which will be split may be modified by
the callback fn, so their copys need to be saved(called split_bio).
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.
The original bios may be modifid by the callback fn before the next
bio_chain_clone() called, when a bio need to be split, so its copy
will be saved.
Signed-off-by: Guangliang Zhao <gzhao@xxxxxxxx>
---
drivers/block/rbd.c | 102 ++++++++++++++++++++++++++++++---------------------
1 file changed, 60 insertions(+), 42 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 9917943..a605e1c 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -717,50 +717,70 @@ 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.
+ * @old: bio to clone
+ * @split_bio: bio which will be split
+ * @offset: start point for bio clone
+ * @len: length of bio chain
+ * @gfp_mask: allocation priority
+ *
+ * Value of split_bio will be !NULL only when there is a bio need to be
+ * split. NULL otherwise.
+ *
+ * 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,
- int len, gfp_t gfpmask)
+static struct bio *bio_chain_clone(struct bio **old, struct bio **split_bio,
+ 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;
- }
+ struct bio *tmp, *old_chain, *split, *new_chain = NULL, *tail = NULL;
+ int total = 0, need = len;
+ split = *split_bio;
+ old_chain = split ? split : *old;
while (old_chain && (total < len)) {
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=%u\n",
- total, len - total, 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;
+ if (!split) {
+ /*
+ * Because the old bio may be modified by the
+ * callback function, its copy should be saved.
+ */
+ split = bio_clone(old_chain, gfpmask);
+ /*
+ * This is always the last allocation in this
+ * loop, so we only need release the bio chain
+ * when failed.
+ */
+ if (!split)
+ goto err_out;
+
+ split->bi_next = old_chain->bi_next;
+ }
} 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;
+ if (split) {
+ bio_put(split);
+ split = NULL;
+ }
}
tmp->bi_bdev = NULL;
@@ -773,9 +793,9 @@ 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;
+ need -= tmp->bi_size;
}
BUG_ON(total < len);
@@ -784,6 +804,7 @@ static struct bio *bio_chain_clone(struct bio **old, struct bio **next,
tail->bi_next = NULL;
*old = old_chain;
+ *split_bio = split;
return new_chain;
@@ -1434,16 +1455,15 @@ 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, *split_bio = NULL;
bool do_write;
unsigned int size;
u64 op_size = 0;
u64 ofs;
- int num_segs, cur_seg = 0;
+ int num_segs, cur_seg = 0, offset = 0;
struct rbd_req_coll *coll;
struct ceph_snap_context *snapc;
@@ -1507,7 +1527,7 @@ 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, &split_bio, &offset,
op_size, GFP_ATOMIC);
if (!bio) {
rbd_coll_end_req_index(rq, coll, cur_seg,
@@ -1535,12 +1555,10 @@ 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);
+ BUG_ON(split_bio);
spin_lock_irq(q->queue_lock);
ceph_put_snap_context(snapc);
--
1.7.10.4
--
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