[BLOCK] blk_rq_map_sg() next_sg fixup

Don't ever use sg_next() on the last entry, it may not be valid!

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 9e3f3cc85d0d..3935469e3662 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1322,8 +1322,8 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
                   struct scatterlist *sglist)
 {
         struct bio_vec *bvec, *bvprv;
-        struct scatterlist *next_sg, *sg;
         struct req_iterator iter;
+        struct scatterlist *sg;
         int nsegs, cluster;
 
         nsegs = 0;
@@ -1333,7 +1333,7 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
          * for each bio in rq
          */
         bvprv = NULL;
-        sg = next_sg = &sglist[0];
+        sg = NULL;
         rq_for_each_segment(bvec, rq, iter) {
                 int nbytes = bvec->bv_len;
 
@@ -1349,8 +1349,10 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
                         sg->length += nbytes;
                 } else {
 new_segment:
-                        sg = next_sg;
-                        next_sg = sg_next(sg);
+                        if (!sg)
+                                sg = sglist;
+                        else
+                                sg = sg_next(sg);
 
                         memset(sg, 0, sizeof(*sg));
                         sg->page = bvec->bv_page;