scatterlist: make sure sg_miter_next() doesn't return 0 sized mappings

Impact: fix not-so-critical but annoying bug

sg_miter_next() returns 0 sized mapping if there is an zero sized sg
entry in the list or at the end of each iteration.  As the users
always check the ->length field, this bug shouldn't be critical other
than causing unnecessary iteration.

Fix it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index b7b449dafbe5..a295e404e908 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -347,9 +347,12 @@ bool sg_miter_next(struct sg_mapping_iter *miter)
         sg_miter_stop(miter);
 
         /* get to the next sg if necessary.  __offset is adjusted by stop */
-        if (miter->__offset == miter->__sg->length && --miter->__nents) {
-                miter->__sg = sg_next(miter->__sg);
-                miter->__offset = 0;
+        while (miter->__offset == miter->__sg->length) {
+                if (--miter->__nents) {
+                        miter->__sg = sg_next(miter->__sg);
+                        miter->__offset = 0;
+                } else
+                        return false;
         }
 
         /* map the next page */