Hi,
在 2025/08/06 1:17, Nilay Shroff 写道:
When a QoS function is removed via rq_qos_del(), and it happens to be the
last QoS function on the request queue, q->rq_qos becomes NULL. In this
case, the QUEUE_FLAG_QOS_ENABLED bit should also be cleared to reflect
that no QoS hooks remain active.
This patch ensures that the QUEUE_FLAG_QOS_ENABLED flag is cleared if the
queue no longer has any associated rq_qos policies. Failing to do so
could cause unnecessary dereferences of a now-null q->rq_qos pointer in
the I/O path.
Signed-off-by: Nilay Shroff <nilay@xxxxxxxxxxxxx>
---
block/blk-rq-qos.c | 2 ++
1 file changed, 2 insertions(+)
There is no fixtag, and can be missing during backport easily.
I feel it's better to fix missing static_branch_dec() in rq_qos_del()
first, and then fix the deadlock problem.
Thanks,
Kuai
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index 460c04715321..654478dfbc20 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -375,6 +375,8 @@ void rq_qos_del(struct rq_qos *rqos)
break;
}
}
+ if (!q->rq_qos)
+ blk_queue_flag_clear(QUEUE_FLAG_QOS_ENABLED, q);
blk_mq_unfreeze_queue(q, memflags);
mutex_lock(&q->debugfs_mutex);
