On Tue, Dec 01, 2020 at 09:02:18PM +0800, John Garry wrote: > 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-ed584b96fa96@xxxxxxxxxx/ > - https://lore.kernel.org/linux-block/5c3ac5af-ed81-11e4-fee3-f92175f14daf@xxxxxxx/T/#m6c1ac11540522716f645d004e2a5a13c9f218908 > - https://lore.kernel.org/linux-block/04e2f9e8-79fa-f1cb-ab23-4a15bf3f64cc@xxxxxxxxx/ > > 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.garry@xxxxxxxxxx> > -- > 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); Seems you didn't address the comment in the following link: https://lore.kernel.org/linux-block/10331543-9e45-ae63-8cdb-17e5a2a3b7ef@xxxxxxxxxx/ The request to be freed may still be refered in another path, such as blk_mq_queue_tag_busy_iter or blk_mq_tagset_busy_iter(), and cmpxchg() doesn't drain/wait for other refers. Thanks, Ming
