It has been reported many times that a use-after-free can be intermittently found when iterating busy requests:
- https://lore.kernel.org/linux-block/8376443a-ec1b-0cef-8244-ed584b96f...@huawei.com/ - https://lore.kernel.org/linux-block/5c3ac5af-ed81-11e4-fee3-f92175f14...@acm.org/T/#m6c1ac11540522716f645d004e2a5a13c9f218908 - https://lore.kernel.org/linux-block/04e2f9e8-79fa-f1cb-ab23-4a15bf3f6...@kernel.dk/ The issue is that when we switch scheduler or change queue nr_requests, the driver tagset may keep references to the stale requests. As a solution, clean up any references to those requests in the driver tagset when freeing. This is done with a cmpxchg to make safe any race with setting the driver tagset request from another queue. Signed-off-by: John Garry <john.ga...@huawei.com> -- Set as RFC as I need to test more. And not sure on solution method, as Bart had another idea. diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index d1eafe2c045c..9b042c7036b3 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -621,7 +621,7 @@ void blk_mq_sched_free_requests(struct request_queue *q) queue_for_each_hw_ctx(q, hctx, i) { if (hctx->sched_tags) - blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i); + blk_mq_free_rqs_ext(q->tag_set, hctx->sched_tags, i, hctx->tags); } } diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 9c92053e704d..562db72e7d79 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -576,7 +576,7 @@ int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx, return -ENOMEM; } - blk_mq_free_rqs(set, *tagsptr, hctx->queue_num); + blk_mq_free_rqs_ext(set, *tagsptr, hctx->queue_num, hctx->tags); blk_mq_free_rq_map(*tagsptr, flags); *tagsptr = new; } else { diff --git a/block/blk-mq.c b/block/blk-mq.c index 55bcee5dc032..f3aad695cd25 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2271,8 +2271,8 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio) return BLK_QC_T_NONE; } -void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, - unsigned int hctx_idx) +void blk_mq_free_rqs_ext(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, + unsigned int hctx_idx, struct blk_mq_tags *references) { struct page *page; @@ -2281,10 +2281,13 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, for (i = 0; i < tags->nr_tags; i++) { struct request *rq = tags->static_rqs[i]; + int j; if (!rq) continue; set->ops->exit_request(set, rq, hctx_idx); + for (j = 0; references && j < references->nr_tags; j++) + cmpxchg(&references->rqs[j], rq, 0); tags->static_rqs[i] = NULL; } } diff --git a/block/blk-mq.h b/block/blk-mq.h index a52703c98b77..53074844e733 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -51,8 +51,10 @@ struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx, /* * Internal helpers for allocating/freeing the request map */ -void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, - unsigned int hctx_idx); +#define blk_mq_free_rqs(set, tags, hctx_idx) \ + blk_mq_free_rqs_ext(set, tags, hctx_idx, NULL) +void blk_mq_free_rqs_ext(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, + unsigned int hctx_idx, struct blk_mq_tags *references); void blk_mq_free_rq_map(struct blk_mq_tags *tags, unsigned int flags); struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set, unsigned int hctx_idx, -- 2.26.2
