From: Qais Yousef qais.yousef@arm.com
[ Upstream commit 315c4f884800c45cb6bd8c90422fad554a8b9588 ]
Commit d81ae8aac85c ("sched/uclamp: Fix initialization of struct uclamp_rq") introduced a bug where uclamp_max of the rq is not reset to match the woken up task's uclamp_max when the rq is idle.
The code was relying on rq->uclamp_max initialized to zero, so on first enqueue
static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p, enum uclamp_id clamp_id) { ...
if (uc_se->value > READ_ONCE(uc_rq->value)) WRITE_ONCE(uc_rq->value, uc_se->value); }
was actually resetting it. But since commit d81ae8aac85c changed the default to 1024, this no longer works. And since rq->uclamp_flags is also initialized to 0, neither above code path nor uclamp_idle_reset() update the rq->uclamp_max on first wake up from idle.
This is only visible from first wake up(s) until the first dequeue to idle after enabling the static key. And it only matters if the uclamp_max of this task is < 1024 since only then its uclamp_max will be effectively ignored.
Fix it by properly initializing rq->uclamp_flags = UCLAMP_FLAG_IDLE to ensure uclamp_idle_reset() is called which then will update the rq uclamp_max value as expected.
Fixes: d81ae8aac85c ("sched/uclamp: Fix initialization of struct uclamp_rq") Signed-off-by: Qais Yousef qais.yousef@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Valentin Schneider Valentin.Schneider@arm.com Tested-by: Dietmar Eggemann dietmar.eggemann@arm.com Link: https://lkml.kernel.org/r/20211202112033.1705279-1-qais.yousef@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 304aad997da11..0a5f9fad45e4b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1526,7 +1526,7 @@ static void __init init_uclamp_rq(struct rq *rq) }; }
- rq->uclamp_flags = 0; + rq->uclamp_flags = UCLAMP_FLAG_IDLE; }
static void __init init_uclamp(void)