On Fri, Aug 02, 2013 at 06:40:27PM +0200, Roger Pau Monne wrote:
> In blkif_queue_request blkfront iterates over the scatterlist in order
> to set the segments of the request, and in blkif_completion blkfront
> iterates over the raw request, which makes it hard to know the exact
> position of the source and destination memory positions.
>
> This can be solved by allocating a scatterlist for each request, that
> will be keep until the request is finished, allowing us to copy the
> data back to the original memory without having to iterate over the
> raw request.
>
> This is a backport of b7649158a0d241f8d53d13ff7441858539e16656 to
> apply against the 3.10-stable tree.
Thank you!
>
> Oracle-Bug: 16660413 - LARGE ASYNCHRONOUS READS APPEAR BROKEN ON 2.6.39-400
> CC: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Reported-by: Anne Milicia <anne.milicia@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Anne Milicia <anne.milicia@xxxxxxxxxx>
> ---
> drivers/block/xen-blkfront.c | 36 +++++++++++++++++-------------------
> 1 files changed, 17 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index d89ef86..69b45fc 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -75,6 +75,7 @@ struct blk_shadow {
> struct blkif_request req;
> struct request *request;
> struct grant *grants_used[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + struct scatterlist sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> };
>
> static DEFINE_MUTEX(blkfront_mutex);
> @@ -98,7 +99,6 @@ struct blkfront_info
> enum blkif_state connected;
> int ring_ref;
> struct blkif_front_ring ring;
> - struct scatterlist sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> unsigned int evtchn, irq;
> struct request_queue *rq;
> struct work_struct work;
> @@ -422,11 +422,11 @@ static int blkif_queue_request(struct request *req)
> ring_req->u.discard.flag = 0;
> } else {
> ring_req->u.rw.nr_segments = blk_rq_map_sg(req->q, req,
> - info->sg);
> + info->shadow[id].sg);
> BUG_ON(ring_req->u.rw.nr_segments >
> BLKIF_MAX_SEGMENTS_PER_REQUEST);
>
> - for_each_sg(info->sg, sg, ring_req->u.rw.nr_segments, i) {
> + for_each_sg(info->shadow[id].sg, sg, ring_req->u.rw.nr_segments, i) {
> fsect = sg->offset >> 9;
> lsect = fsect + (sg->length >> 9) - 1;
>
> @@ -867,12 +867,12 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
> struct blkif_response *bret)
> {
> int i = 0;
> - struct bio_vec *bvec;
> - struct req_iterator iter;
> - unsigned long flags;
> + struct scatterlist *sg;
> char *bvec_data;
> void *shared_data;
> - unsigned int offset = 0;
> + int nseg;
> +
> + nseg = s->req.u.rw.nr_segments;
>
> if (bret->operation == BLKIF_OP_READ) {
> /*
> @@ -881,19 +881,16 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
> * than PAGE_SIZE, we have to keep track of the current offset,
> * to be sure we are copying the data from the right shared page.
> */
> - rq_for_each_segment(bvec, s->request, iter) {
> - BUG_ON((bvec->bv_offset + bvec->bv_len) > PAGE_SIZE);
> - if (bvec->bv_offset < offset)
> - i++;
> - BUG_ON(i >= s->req.u.rw.nr_segments);
> + for_each_sg(s->sg, sg, nseg, i) {
> + BUG_ON(sg->offset + sg->length > PAGE_SIZE);
> shared_data = kmap_atomic(
> pfn_to_page(s->grants_used[i]->pfn));
> - bvec_data = bvec_kmap_irq(bvec, &flags);
> - memcpy(bvec_data, shared_data + bvec->bv_offset,
> - bvec->bv_len);
> - bvec_kunmap_irq(bvec_data, &flags);
> + bvec_data = kmap_atomic(sg_page(sg));
> + memcpy(bvec_data + sg->offset,
> + shared_data + sg->offset,
> + sg->length);
> + kunmap_atomic(bvec_data);
> kunmap_atomic(shared_data);
> - offset = bvec->bv_offset + bvec->bv_len;
> }
> }
> /* Add the persistent grant into the list of free grants */
> @@ -1022,7 +1019,7 @@ static int setup_blkring(struct xenbus_device *dev,
> struct blkfront_info *info)
> {
> struct blkif_sring *sring;
> - int err;
> + int err, i;
>
> info->ring_ref = GRANT_INVALID_REF;
>
> @@ -1034,7 +1031,8 @@ static int setup_blkring(struct xenbus_device *dev,
> SHARED_RING_INIT(sring);
> FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
>
> - sg_init_table(info->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
> + for (i = 0; i < BLK_RING_SIZE; i++)
> + sg_init_table(info->shadow[i].sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
>
> /* Allocate memory for grants */
> err = fill_grant_buffer(info, BLK_RING_SIZE *
> --
> 1.7.7.5 (Apple Git-26)
>
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