block: deal with stale req count of plug list

In both legacy and mq path, req count of plug list is computed before allocating request, so the number can be stale when falling back to slept allocation, also the new introduced wbt can sleep too. This patch deals with the case by checking if plug list becomes empty, and fixes the KASAN report of 'BUG: KASAN: stack-out-of-bounds' which is introduced by Shaohua's patches of dispatching big request. Fixes: 600271d(blk-mq: immediately dispatch big size request) Fixes: 50d24c3(block: immediately dispatch big size request) Cc: Shaohua Li <[email protected]> Signed-off-by: Ming Lei <[email protected]> Signed-off-by: Jens Axboe <[email protected]>
mrcsosa · Nov 16, 2016 · 0a6219a · 0a6219a
1 parent 2868f13
commit 0a6219a
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Showing 2 changed files with 11 additions and 1 deletion.
diff --git a/block/blk-core.c b/block/blk-core.c
@@ -1753,8 +1753,11 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 		/*
 		 * If this is the first request added after a plug, fire
 		 * of a plug trace.
+		 *
+		 * @request_count may become stale because of schedule
+		 * out, so check plug list again.
 		 */
-		if (!request_count)
+		if (!request_count || list_empty(&plug->list))
 			trace_block_plug(q);
 		else {
 			struct request *last = list_entry_rq(plug->list.prev);

diff --git a/block/blk-mq.c b/block/blk-mq.c
@@ -1497,6 +1497,13 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 		struct request *last = NULL;
 
 		blk_mq_bio_to_request(rq, bio);
+
+		/*
+		 * @request_count may become stale because of schedule
+		 * out, so check the list again.
+		 */
+		if (list_empty(&plug->mq_list))
+			request_count = 0;
 		if (!request_count)
 			trace_block_plug(q);
 		else