Hi,
在 2025/09/09 14:39, Nilay Shroff 写道:
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.
I already access q->elevator to check input nr from patch 4, and that's
why I add comments to explain switching elevator is serialized, is this
enough?
Thanks,
Kuai
Thanks,
--Nilay
.
