From: Yu Kuai <yukuai3@huawei.com>
request_queue->nr_requests can be changed by:
a) switching elevator by update nr_hw_queues
b) switching elevator by elevator sysfs attribute
c) configue queue sysfs attribute nr_requests
Current lock order is:
1) update_nr_hwq_lock, case a,b
- allocate elevator tags
2) freeze_queue
3) elevator_lock, cas a,b,c
- update nr_requests
The update_nr_hwq_lock is not held by case c for now, and we need to check
nr_requests while elevator_lock is held, however, we can't allocate
elevator_tags whih queue freezed.
Hence also require update_nr_hwq_lock and check nr_requests, make it
possible to allocate new elevator_tags without queue freezed, also
prevent nr_requests to be changed concurrently by other contexts.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
block/blk-sysfs.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index f3d08edcc34f..37eae7927b45 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -68,13 +68,14 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count)
int ret, err;
unsigned int memflags;
struct request_queue *q = disk->queue;
+ struct blk_mq_tag_set *set = q->tag_set;
ret = queue_var_store(&nr, page, count);
if (ret < 0)
return ret;
- memflags = blk_mq_freeze_queue(q);
- mutex_lock(&q->elevator_lock);
+ /* serialize with switching elevator */
+ down_write(&set->update_nr_hwq_lock);
if (q->nr_requests == nr)
goto unlock;
@@ -89,13 +90,17 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count)
goto unlock;
}
+ memflags = blk_mq_freeze_queue(q);
+ mutex_lock(&q->elevator_lock);
err = blk_mq_update_nr_requests(disk->queue, nr);
if (err)
ret = err;
-unlock:
mutex_unlock(&q->elevator_lock);
blk_mq_unfreeze_queue(q, memflags);
+
+unlock:
+ up_write(&set->update_nr_hwq_lock);
return ret;
}
--
2.39.2