Igor Raits and Bagas Sanjaya report a RQCF_ACT_SKIP leak warning. Link: https://lore.kernel.org/all/a5dd536d-041a-2ce9-f4b7-64d8d85c86dc@gmail.com

This warning may be triggered in the following situations:

CPU0 CPU1

__schedule() *rq->clock_update_flags <<= 1;* unregister_fair_sched_group() pick_next_task_fair+0x4a/0x410 destroy_cfs_bandwidth() newidle_balance+0x115/0x3e0 for_each_possible_cpu(i) *i=0* rq_unpin_lock(this_rq, rf) __cfsb_csd_unthrottle() raw_spin_rq_unlock(this_rq) rq_lock(*CPU0_rq*, &rf) rq_clock_start_loop_update() rq->clock_update_flags & RQCF_ACT_SKIP <-- raw_spin_rq_lock(this_rq)

The purpose of RQCF_ACT_SKIP is to skip the update rq clock, but the update is very early in __schedule(), but we clear RQCF_*_SKIP very late, causing it to span that gap above and triggering this warning.

In __schedule() we can clear the RQCF_*_SKIP flag immediately after update_rq_clock() to avoid this RQCF_ACT_SKIP leak warning. And set rq->clock_update_flags to RQCF_UPDATED to avoid rq->clock_update_flags < RQCF_ACT_SKIP warning that may be triggered later.

Fixes: ebb83d84e49b ("sched/core: Avoid multiple calling update_rq_clock() in __cfsb_csd_unthrottle()") Cc: stable@vger.kernel.org Reported-by: Igor Raits igor.raits@gmail.com Reported-by: Bagas Sanjaya bagasdotme@gmail.com Closes: https://lore.kernel.org/all/20230913082424.73252-1-jiahao.os@bytedance.com Suggested-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Hao Jia jiahao.os@bytedance.com --- kernel/sched/core.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 802551e0009b..afb8d213155b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5374,8 +5374,6 @@ context_switch(struct rq *rq, struct task_struct *prev, /* switch_mm_cid() requires the memory barriers above. */ switch_mm_cid(rq, prev, next);

- rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP); - prepare_lock_switch(rq, next, rf);

/* Here we just switch the register state and the stack. */ @@ -6615,6 +6613,7 @@ static void __sched notrace __schedule(unsigned int sched_mode) /* Promote REQ to ACT */ rq->clock_update_flags <<= 1; update_rq_clock(rq); + rq->clock_update_flags = RQCF_UPDATED;

switch_count = &prev->nivcsw;

@@ -6694,8 +6693,6 @@ static void __sched notrace __schedule(unsigned int sched_mode) /* Also unlocks the rq: */ rq = context_switch(rq, prev, next, &rf); } else { - rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP); - rq_unpin_lock(rq, &rf); __balance_callbacks(rq); raw_spin_rq_unlock_irq(rq);