Re: [PATCHv3 2/3] block: decrement block_rq_qos static key in rq_qos_del()
From: Yu Kuai <hidden>
Date: 2025-08-14 09:14:55
Hi, 在 2025/08/14 16:24, Nilay Shroff 写道:
rq_qos_add() increments the block_rq_qos static key when a QoS policy is attached. When a QoS policy is removed via rq_qos_del(), we must symmetrically decrement the static key. If this removal drops the last QoS policy from the queue (q->rq_qos becomes NULL), the static branch can be disabled and the jump label patched to a NOP, avoiding overhead on the hot path. This change ensures rq_qos_add()/rq_qos_del() keep the block_rq_qos static key balanced and prevents leaving the branch permanently enabled after the last policy is removed.
BTW, this problem is unlikely to happen in real users cases, because rq_qos_del is only called from error path, where activate cgroup policy failed with -ENOMEM.
quoted hunk ↗ jump to hunk
Fixes: 033b667a823e ("block: blk-rq-qos: guard rq-qos helpers by static key") Signed-off-by: Nilay Shroff <redacted> --- block/blk-rq-qos.c | 1 + 1 file changed, 1 insertion(+)diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index 848591fb3c57..b1e24bb85ad2 100644 --- a/block/blk-rq-qos.c +++ b/block/blk-rq-qos.c@@ -374,6 +374,7 @@ void rq_qos_del(struct rq_qos *rqos) for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) { if (*cur == rqos) { *cur = rqos->next; + static_branch_dec(&block_rq_qos); break; } }
Reviewed-by: Yu Kuai <redacted> Thanks