blk-mq: fix false negative out-of-tags condition

[mirror_ubuntu-zesty-kernel.git] / block / blk-mq-tag.c

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 60c9d4a93fe470ced7471cd8653d8a00fc8922d7..d4daee385a235ebd7c8bb86c3ecbaef74e46f233 100644 (file)
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -142,29 +142,30 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 
 static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
 {
-       int tag, org_last_tag, end;
-       bool wrap = last_tag != 0;
+       int tag, org_last_tag = last_tag;
 
-       org_last_tag = last_tag;
-       end = bm->depth;
-       do {
-restart:
-               tag = find_next_zero_bit(&bm->word, end, last_tag);
-               if (unlikely(tag >= end)) {
+       while (1) {
+               tag = find_next_zero_bit(&bm->word, bm->depth, last_tag);
+               if (unlikely(tag >= bm->depth)) {
                        /*
-                        * We started with an offset, start from 0 to
+                        * We started with an offset, and we didn't reset the
+                        * offset to 0 in a failure case, so start from 0 to
                         * exhaust the map.
                         */
-                       if (wrap) {
-                               wrap = false;
-                               end = org_last_tag;
-                               last_tag = 0;
-                               goto restart;
+                       if (org_last_tag && last_tag) {
+                               last_tag = org_last_tag = 0;
+                               continue;
                        }
                        return -1;
                }
+
+               if (!test_and_set_bit(tag, &bm->word))
+                       break;
+
                last_tag = tag + 1;
-       } while (test_and_set_bit(tag, &bm->word));
+               if (last_tag >= bm->depth - 1)
+                       last_tag = 0;
+       }
 
        return tag;
 }
@@ -199,9 +200,17 @@ static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
                        goto done;
                }
 
-               last_tag = 0;
-               if (++index >= bt->map_nr)
+               /*
+                * Jump to next index, and reset the last tag to be the
+                * first tag of that index
+                */
+               index++;
+               last_tag = (index << bt->bits_per_word);
+
+               if (index >= bt->map_nr) {
                        index = 0;
+                       last_tag = 0;
+               }
        }
 
        *tag_cache = 0;