The following commit has been merged into the sched/urgent branch of tip: Commit-ID: 975707f227b07a8212060f94447171d15d7a681b Gitweb: https://git.kernel.org/tip/975707f227b07a8212060f94447171d15d7a681b Author: Peter Zijlstra <[email protected]> AuthorDate: Wed, 20 Jan 2021 15:05:41 +01:00 Committer: Peter Zijlstra <[email protected]> CommitterDate: Fri, 22 Jan 2021 15:09:43 +01:00
sched: Prepare to use balance_push in ttwu() In preparation of using the balance_push state in ttwu() we need it to provide a reliable and consistent state. The immediate problem is that rq->balance_callback gets cleared every schedule() and then re-set in the balance_push_callback() itself. This is not a reliable signal, so add a variable that stays set during the entire time. Also move setting it before the synchronize_rcu() in sched_cpu_deactivate(), such that we get guaranteed visibility to ttwu(), which is a preempt-disable region. Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Reviewed-by: Valentin Schneider <[email protected]> Tested-by: Valentin Schneider <[email protected]> Link: https://lkml.kernel.org/r/[email protected] --- kernel/sched/core.c | 11 ++++++----- kernel/sched/sched.h | 1 + 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8da0fd7..16946b5 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7320,6 +7320,7 @@ static void balance_push_set(int cpu, bool on) struct rq_flags rf; rq_lock_irqsave(rq, &rf); + rq->balance_push = on; if (on) { WARN_ON_ONCE(rq->balance_callback); rq->balance_callback = &balance_push_callback; @@ -7489,17 +7490,17 @@ int sched_cpu_deactivate(unsigned int cpu) int ret; set_cpu_active(cpu, false); + balance_push_set(cpu, true); + /* - * We've cleared cpu_active_mask, wait for all preempt-disabled and RCU - * users of this state to go away such that all new such users will - * observe it. + * We've cleared cpu_active_mask / set balance_push, wait for all + * preempt-disabled and RCU users of this state to go away such that + * all new such users will observe it. * * Do sync before park smpboot threads to take care the rcu boost case. */ synchronize_rcu(); - balance_push_set(cpu, true); - rq_lock_irqsave(rq, &rf); if (rq->rd) { update_rq_clock(rq); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 12ada79..bb09988 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -975,6 +975,7 @@ struct rq { unsigned long cpu_capacity_orig; struct callback_head *balance_callback; + unsigned char balance_push; unsigned char nohz_idle_balance; unsigned char idle_balance;
