The following commit has been merged into the sched/core branch of tip: Commit-ID: 3015ef4b98f53fe7eba4f5f82f562c0e074d213c Gitweb: https://git.kernel.org/tip/3015ef4b98f53fe7eba4f5f82f562c0e074d213c Author: Thomas Gleixner <t...@linutronix.de> AuthorDate: Wed, 26 Aug 2020 14:08:10 +02:00 Committer: Peter Zijlstra <pet...@infradead.org> CommitterDate: Tue, 10 Nov 2020 18:39:00 +01:00
sched/core: Make migrate disable and CPU hotplug cooperative On CPU unplug tasks which are in a migrate disabled region cannot be pushed to a different CPU until they returned to migrateable state. Account the number of tasks on a runqueue which are in a migrate disabled section and make the hotplug wait mechanism respect that. Signed-off-by: Thomas Gleixner <t...@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Reviewed-by: Valentin Schneider <valentin.schnei...@arm.com> Reviewed-by: Daniel Bristot de Oliveira <bris...@redhat.com> Link: https://lkml.kernel.org/r/20201023102347.067278...@infradead.org --- kernel/sched/core.c | 36 ++++++++++++++++++++++++++++++------ kernel/sched/sched.h | 4 ++++ 2 files changed, 34 insertions(+), 6 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0efc1e4..6ea593c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1721,10 +1721,17 @@ static void migrate_disable_switch(struct rq *rq, struct task_struct *p) void migrate_disable(void) { - if (current->migration_disabled++) + struct task_struct *p = current; + + if (p->migration_disabled) { + p->migration_disabled++; return; + } - barrier(); + preempt_disable(); + this_rq()->nr_pinned++; + p->migration_disabled = 1; + preempt_enable(); } EXPORT_SYMBOL_GPL(migrate_disable); @@ -1751,6 +1758,7 @@ void migrate_enable(void) */ barrier(); p->migration_disabled = 0; + this_rq()->nr_pinned--; preempt_enable(); } EXPORT_SYMBOL_GPL(migrate_enable); @@ -1760,6 +1768,11 @@ static inline bool is_migration_disabled(struct task_struct *p) return p->migration_disabled; } +static inline bool rq_has_pinned_tasks(struct rq *rq) +{ + return rq->nr_pinned; +} + #endif /* @@ -2693,6 +2706,11 @@ static inline bool is_migration_disabled(struct task_struct *p) return false; } +static inline bool rq_has_pinned_tasks(struct rq *rq) +{ + return false; +} + #endif static void @@ -7066,15 +7084,20 @@ static void balance_push(struct rq *rq) * Both the cpu-hotplug and stop task are in this case and are * required to complete the hotplug process. */ - if (is_per_cpu_kthread(push_task)) { + if (is_per_cpu_kthread(push_task) || is_migration_disabled(push_task)) { /* * If this is the idle task on the outgoing CPU try to wake * up the hotplug control thread which might wait for the * last task to vanish. The rcuwait_active() check is * accurate here because the waiter is pinned on this CPU * and can't obviously be running in parallel. + * + * On RT kernels this also has to check whether there are + * pinned and scheduled out tasks on the runqueue. They + * need to leave the migrate disabled section first. */ - if (!rq->nr_running && rcuwait_active(&rq->hotplug_wait)) { + if (!rq->nr_running && !rq_has_pinned_tasks(rq) && + rcuwait_active(&rq->hotplug_wait)) { raw_spin_unlock(&rq->lock); rcuwait_wake_up(&rq->hotplug_wait); raw_spin_lock(&rq->lock); @@ -7121,7 +7144,8 @@ static void balance_hotplug_wait(void) { struct rq *rq = this_rq(); - rcuwait_wait_event(&rq->hotplug_wait, rq->nr_running == 1, + rcuwait_wait_event(&rq->hotplug_wait, + rq->nr_running == 1 && !rq_has_pinned_tasks(rq), TASK_UNINTERRUPTIBLE); } @@ -7366,7 +7390,7 @@ int sched_cpu_dying(unsigned int cpu) sched_tick_stop(cpu); rq_lock_irqsave(rq, &rf); - BUG_ON(rq->nr_running != 1); + BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq)); rq_unlock_irqrestore(rq, &rf); calc_load_migrate(rq); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 72d8e47..42de140 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1053,6 +1053,10 @@ struct rq { /* Must be inspected within a rcu lock section */ struct cpuidle_state *idle_state; #endif + +#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP) + unsigned int nr_pinned; +#endif }; #ifdef CONFIG_FAIR_GROUP_SCHED
