On 9/8/25 11:45 AM, Yu Kuai wrote: > From: Yu Kuai <yukuai3@xxxxxxxxxx> > > Allocate and free sched_tags while queue is freezed can deadlock[1], > this is a long term problem, hence allocate memory before freezing > queue and free memory after queue is unfreezed. > > [1] https://lore.kernel.org/all/0659ea8d-a463-47c8-9180-43c719e106eb@xxxxxxxxxxxxx/ > Fixes: e3a2b3f931f5 ("blk-mq: allow changing of queue depth through sysfs") > > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx> [...] [...] > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > index 7ea15bf68b4b..a0a7ebad378f 100644 > --- a/block/blk-sysfs.c > +++ b/block/blk-sysfs.c > @@ -64,11 +64,12 @@ static ssize_t queue_requests_show(struct gendisk *disk, char *page) > static ssize_t > queue_requests_store(struct gendisk *disk, const char *page, size_t count) > { > - unsigned long nr; > - int ret, err; > - unsigned int memflags; > struct request_queue *q = disk->queue; > struct blk_mq_tag_set *set = q->tag_set; > + struct elevator_tags *et = NULL; > + unsigned int memflags; > + unsigned long nr; > + int ret; > > ret = queue_var_store(&nr, page, count); > if (ret < 0) > @@ -90,16 +91,24 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) > goto unlock; > } > > + if (q->elevator && nr > q->elevator->et->nr_requests) { > + /* allocate memory before freezing queue to prevent deadlock */ > + et = blk_mq_alloc_sched_tags(set, q->nr_hw_queues, nr); > + if (!et) { > + ret = -ENOMEM; > + goto unlock; > + } > + } > + I think we should add a comment above explaining why is it safe to access q->elevator without holding ->elevator_lock. Thanks, --Nilay
