On Tue, Jul 24, 2012 at 12:28:47PM -0700, Yehuda Sadeh wrote:
> On Mon, Jul 23, 2012 at 11:06 PM, Guangliang Zhao <gzhao@xxxxxxxx> wrote:
> >
> > 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 chian from the origin directly, doesn't use
> > bio_split(without bio_pair). The new bio chain can be release
> > whenever we don't need it.
> >
> > Signed-off-by: Guangliang Zhao <gzhao@xxxxxxxx>
> > ---
> > 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..5aa45fa 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_offset -= *offset;
>
> offset is the position within the bio chain, bv_offset is the offset
> within the specific page. Does this make sense?
Sorry for that mistake, it should be:
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
> >
> --
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Thanks for you reply.
--
Best regards,
Guangliang
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