diff options
Diffstat (limited to 'kernel/sched/core.c')
| -rw-r--r-- | kernel/sched/core.c | 1104 |
1 files changed, 859 insertions, 245 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e0948cbb1d70..3636b80222ac 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -97,7 +97,7 @@ int sysctl_sched_rt_runtime = 950000; * * Normal scheduling state is serialized by rq->lock. __schedule() takes the * local CPU's rq->lock, it optionally removes the task from the runqueue and - * always looks at the local rq data structures to find the most elegible task + * always looks at the local rq data structures to find the most eligible task * to run next. * * Task enqueue is also under rq->lock, possibly taken from another CPU. @@ -320,14 +320,6 @@ void update_rq_clock(struct rq *rq) update_rq_clock_task(rq, delta); } -static inline void -rq_csd_init(struct rq *rq, call_single_data_t *csd, smp_call_func_t func) -{ - csd->flags = 0; - csd->func = func; - csd->info = rq; -} - #ifdef CONFIG_SCHED_HRTICK /* * Use HR-timers to deliver accurate preemption points. @@ -428,7 +420,7 @@ void hrtick_start(struct rq *rq, u64 delay) static void hrtick_rq_init(struct rq *rq) { #ifdef CONFIG_SMP - rq_csd_init(rq, &rq->hrtick_csd, __hrtick_start); + INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq); #endif hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD); rq->hrtick_timer.function = hrtick; @@ -518,7 +510,7 @@ static bool __wake_q_add(struct wake_q_head *head, struct task_struct *task) /* * Atomically grab the task, if ->wake_q is !nil already it means - * its already queued (either by us or someone else) and will get the + * it's already queued (either by us or someone else) and will get the * wakeup due to that. * * In order to ensure that a pending wakeup will observe our pending @@ -769,7 +761,7 @@ bool sched_can_stop_tick(struct rq *rq) return false; /* - * If there are more than one RR tasks, we need the tick to effect the + * If there are more than one RR tasks, we need the tick to affect the * actual RR behaviour. */ if (rq->rt.rr_nr_running) { @@ -1187,14 +1179,14 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p, * accounting was performed at enqueue time and we can just return * here. * - * Need to be careful of the following enqeueue/dequeue ordering + * Need to be careful of the following enqueue/dequeue ordering * problem too * * enqueue(taskA) * // sched_uclamp_used gets enabled * enqueue(taskB) * dequeue(taskA) - * // Must not decrement bukcet->tasks here + * // Must not decrement bucket->tasks here * dequeue(taskB) * * where we could end up with stale data in uc_se and @@ -1413,17 +1405,24 @@ done: static int uclamp_validate(struct task_struct *p, const struct sched_attr *attr) { - unsigned int lower_bound = p->uclamp_req[UCLAMP_MIN].value; - unsigned int upper_bound = p->uclamp_req[UCLAMP_MAX].value; + int util_min = p->uclamp_req[UCLAMP_MIN].value; + int util_max = p->uclamp_req[UCLAMP_MAX].value; - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) - lower_bound = attr->sched_util_min; - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) - upper_bound = attr->sched_util_max; + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { + util_min = attr->sched_util_min; - if (lower_bound > upper_bound) - return -EINVAL; - if (upper_bound > SCHED_CAPACITY_SCALE) + if (util_min + 1 > SCHED_CAPACITY_SCALE + 1) + return -EINVAL; + } + + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { + util_max = attr->sched_util_max; + + if (util_max + 1 > SCHED_CAPACITY_SCALE + 1) + return -EINVAL; + } + + if (util_min != -1 && util_max != -1 && util_min > util_max) return -EINVAL; /* @@ -1438,20 +1437,41 @@ static int uclamp_validate(struct task_struct *p, return 0; } +static bool uclamp_reset(const struct sched_attr *attr, + enum uclamp_id clamp_id, + struct uclamp_se *uc_se) +{ + /* Reset on sched class change for a non user-defined clamp value. */ + if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)) && + !uc_se->user_defined) + return true; + + /* Reset on sched_util_{min,max} == -1. */ + if (clamp_id == UCLAMP_MIN && + attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN && + attr->sched_util_min == -1) { + return true; + } + + if (clamp_id == UCLAMP_MAX && + attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX && + attr->sched_util_max == -1) { + return true; + } + + return false; +} + static void __setscheduler_uclamp(struct task_struct *p, const struct sched_attr *attr) { enum uclamp_id clamp_id; - /* - * On scheduling class change, reset to default clamps for tasks - * without a task-specific value. - */ for_each_clamp_id(clamp_id) { struct uclamp_se *uc_se = &p->uclamp_req[clamp_id]; + unsigned int value; - /* Keep using defined clamps across class changes */ - if (uc_se->user_defined) + if (!uclamp_reset(attr, clamp_id, uc_se)) continue; /* @@ -1459,21 +1479,25 @@ static void __setscheduler_uclamp(struct task_struct *p, * at runtime. */ if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN)) - __uclamp_update_util_min_rt_default(p); + value = sysctl_sched_uclamp_util_min_rt_default; else - uclamp_se_set(uc_se, uclamp_none(clamp_id), false); + value = uclamp_none(clamp_id); + + uclamp_se_set(uc_se, value, false); } if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP))) return; - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN && + attr->sched_util_min != -1) { uclamp_se_set(&p->uclamp_req[UCLAMP_MIN], attr->sched_util_min, true); } - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX && + attr->sched_util_max != -1) { uclamp_se_set(&p->uclamp_req[UCLAMP_MAX], attr->sched_util_max, true); } @@ -1696,6 +1720,76 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags) #ifdef CONFIG_SMP +static void +__do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags); + +static int __set_cpus_allowed_ptr(struct task_struct *p, + const struct cpumask *new_mask, + u32 flags); + +static void migrate_disable_switch(struct rq *rq, struct task_struct *p) +{ + if (likely(!p->migration_disabled)) + return; + + if (p->cpus_ptr != &p->cpus_mask) + return; + + /* + * Violates locking rules! see comment in __do_set_cpus_allowed(). + */ + __do_set_cpus_allowed(p, cpumask_of(rq->cpu), SCA_MIGRATE_DISABLE); +} + +void migrate_disable(void) +{ + struct task_struct *p = current; + + if (p->migration_disabled) { + p->migration_disabled++; + return; + } + + preempt_disable(); + this_rq()->nr_pinned++; + p->migration_disabled = 1; + preempt_enable(); +} +EXPORT_SYMBOL_GPL(migrate_disable); + +void migrate_enable(void) +{ + struct task_struct *p = current; + + if (p->migration_disabled > 1) { + p->migration_disabled--; + return; + } + + /* + * Ensure stop_task runs either before or after this, and that + * __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule(). + */ + preempt_disable(); + if (p->cpus_ptr != &p->cpus_mask) + __set_cpus_allowed_ptr(p, &p->cpus_mask, SCA_MIGRATE_ENABLE); + /* + * Mustn't clear migration_disabled() until cpus_ptr points back at the + * regular cpus_mask, otherwise things that race (eg. + * select_fallback_rq) get confused. + */ + barrier(); + p->migration_disabled = 0; + this_rq()->nr_pinned--; + preempt_enable(); +} +EXPORT_SYMBOL_GPL(migrate_enable); + +static inline bool rq_has_pinned_tasks(struct rq *rq) +{ + return rq->nr_pinned; +} + /* * Per-CPU kthreads are allowed to run on !active && online CPUs, see * __set_cpus_allowed_ptr() and select_fallback_rq(). @@ -1705,7 +1799,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu) if (!cpumask_test_cpu(cpu, p->cpus_ptr)) return false; - if (is_per_cpu_kthread(p)) + if (is_per_cpu_kthread(p) || is_migration_disabled(p)) return cpu_online(cpu); return cpu_active(cpu); @@ -1750,8 +1844,16 @@ static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf, } struct migration_arg { - struct task_struct *task; - int dest_cpu; + struct task_struct *task; + int dest_cpu; + struct set_affinity_pending *pending; +}; + +struct set_affinity_pending { + refcount_t refs; + struct completion done; + struct cpu_stop_work stop_work; + struct migration_arg arg; }; /* @@ -1783,16 +1885,19 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf, */ static int migration_cpu_stop(void *data) { + struct set_affinity_pending *pending; struct migration_arg *arg = data; struct task_struct *p = arg->task; + int dest_cpu = arg->dest_cpu; struct rq *rq = this_rq(); + bool complete = false; struct rq_flags rf; /* * The original target CPU might have gone down and we might * be on another CPU but it doesn't matter. */ - local_irq_disable(); + local_irq_save(rf.flags); /* * We need to explicitly wake pending tasks before running * __migrate_task() such that we will not miss enforcing cpus_ptr @@ -1802,21 +1907,137 @@ static int migration_cpu_stop(void *data) raw_spin_lock(&p->pi_lock); rq_lock(rq, &rf); + + pending = p->migration_pending; /* * If task_rq(p) != rq, it cannot be migrated here, because we're * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because * we're holding p->pi_lock. */ if (task_rq(p) == rq) { + if (is_migration_disabled(p)) + goto out; + + if (pending) { + p->migration_pending = NULL; + complete = true; + } + + /* migrate_enable() -- we must not race against SCA */ + if (dest_cpu < 0) { + /* + * When this was migrate_enable() but we no longer + * have a @pending, a concurrent SCA 'fixed' things + * and we should be valid again. Nothing to do. + */ + if (!pending) { + WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)); + goto out; + } + + dest_cpu = cpumask_any_distribute(&p->cpus_mask); + } + if (task_on_rq_queued(p)) - rq = __migrate_task(rq, &rf, p, arg->dest_cpu); + rq = __migrate_task(rq, &rf, p, dest_cpu); else - p->wake_cpu = arg->dest_cpu; + p->wake_cpu = dest_cpu; + + } else if (dest_cpu < 0 || pending) { + /* + * This happens when we get migrated between migrate_enable()'s + * preempt_enable() and scheduling the stopper task. At that + * point we're a regular task again and not current anymore. + * + * A !PREEMPT kernel has a giant hole here, which makes it far + * more likely. + */ + + /* + * The task moved before the stopper got to run. We're holding + * ->pi_lock, so the allowed mask is stable - if it got + * somewhere allowed, we're done. + */ + if (pending && cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) { + p->migration_pending = NULL; + complete = true; + goto out; + } + + /* + * When this was migrate_enable() but we no longer have an + * @pending, a concurrent SCA 'fixed' things and we should be + * valid again. Nothing to do. + */ + if (!pending) { + WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)); + goto out; + } + + /* + * When migrate_enable() hits a rq mis-match we can't reliably + * determine is_migration_disabled() and so have to chase after + * it. + */ + task_rq_unlock(rq, p, &rf); + stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop, + &pending->arg, &pending->stop_work); + return 0; } - rq_unlock(rq, &rf); - raw_spin_unlock(&p->pi_lock); +out: + task_rq_unlock(rq, p, &rf); + + if (complete) + complete_all(&pending->done); + + /* For pending->{arg,stop_work} */ + pending = arg->pending; + if (pending && refcount_dec_and_test(&pending->refs)) + wake_up_var(&pending->refs); - local_irq_enable(); + return 0; +} + +int push_cpu_stop(void *arg) +{ + struct rq *lowest_rq = NULL, *rq = this_rq(); + struct task_struct *p = arg; + + raw_spin_lock_irq(&p->pi_lock); + raw_spin_lock(&rq->lock); + + if (task_rq(p) != rq) + goto out_unlock; + + if (is_migration_disabled(p)) { + p->migration_flags |= MDF_PUSH; + goto out_unlock; + } + + p->migration_flags &= ~MDF_PUSH; + + if (p->sched_class->find_lock_rq) + lowest_rq = p->sched_class->find_lock_rq(p, rq); + + if (!lowest_rq) + goto out_unlock; + + // XXX validate p is still the highest prio task + if (task_rq(p) == rq) { + deactivate_task(rq, p, 0); + set_task_cpu(p, lowest_rq->cpu); + activate_task(lowest_rq, p, 0); + resched_curr(lowest_rq); + } + + double_unlock_balance(rq, lowest_rq); + +out_unlock: + rq->push_busy = false; + raw_spin_unlock(&rq->lock); + raw_spin_unlock_irq(&p->pi_lock); + + put_task_struct(p); return 0; } @@ -1824,18 +2045,39 @@ static int migration_cpu_stop(void *data) * sched_class::set_cpus_allowed must do the below, but is not required to * actually call this function. */ -void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask) +void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask, u32 flags) { + if (flags & (SCA_MIGRATE_ENABLE | SCA_MIGRATE_DISABLE)) { + p->cpus_ptr = new_mask; + return; + } + cpumask_copy(&p->cpus_mask, new_mask); p->nr_cpus_allowed = cpumask_weight(new_mask); } -void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) +static void +__do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 flags) { struct rq *rq = task_rq(p); bool queued, running; - lockdep_assert_held(&p->pi_lock); + /* + * This here violates the locking rules for affinity, since we're only + * supposed to change these variables while holding both rq->lock and + * p->pi_lock. + * + * HOWEVER, it magically works, because ttwu() is the only code that + * accesses these variables under p->pi_lock and only does so after + * smp_cond_load_acquire(&p->on_cpu, !VAL), and we're in __schedule() + * before finish_task(). + * + * XXX do further audits, this smells like something putrid. + */ + if (flags & SCA_MIGRATE_DISABLE) + SCHED_WARN_ON(!p->on_cpu); + else + lockdep_assert_held(&p->pi_lock); queued = task_on_rq_queued(p); running = task_current(rq, p); @@ -1851,7 +2093,7 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) if (running) put_prev_task(rq, p); - p->sched_class->set_cpus_allowed(p, new_mask); + p->sched_class->set_cpus_allowed(p, new_mask, flags); if (queued) enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK); @@ -1859,6 +2101,208 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) set_next_task(rq, p); } +void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) +{ + __do_set_cpus_allowed(p, new_mask, 0); +} + +/* + * This function is wildly self concurrent; here be dragons. + * + * + * When given a valid mask, __set_cpus_allowed_ptr() must block until the + * designated task is enqueued on an allowed CPU. If that task is currently + * running, we have to kick it out using the CPU stopper. + * + * Migrate-Disable comes along and tramples all over our nice sandcastle. + * Consider: + * + * Initial conditions: P0->cpus_mask = [0, 1] + * + * P0@CPU0 P1 + * + * migrate_disable(); + * <preempted> + * set_cpus_allowed_ptr(P0, [1]); + * + * P1 *cannot* return from this set_cpus_allowed_ptr() call until P0 executes + * its outermost migrate_enable() (i.e. it exits its Migrate-Disable region). + * This means we need the following scheme: + * + * P0@CPU0 P1 + * + * migrate_disable(); + * <preempted> + * set_cpus_allowed_ptr(P0, [1]); + * <blocks> + * <resumes> + * migrate_enable(); + * __set_cpus_allowed_ptr(); + * <wakes local stopper> + * `--> <woken on migration completion> + * + * Now the fun stuff: there may be several P1-like tasks, i.e. multiple + * concurrent set_cpus_allowed_ptr(P0, [*]) calls. CPU affinity changes of any + * task p are serialized by p->pi_lock, which we can leverage: the one that + * should come into effect at the end of the Migrate-Disable region is the last + * one. This means we only need to track a single cpumask (i.e. p->cpus_mask), + * but we still need to properly signal those waiting tasks at the appropriate + * moment. + * + * This is implemented using struct set_affinity_pending. The first + * __set_cpus_allowed_ptr() caller within a given Migrate-Disable region will + * setup an instance of that struct and install it on the targeted task_struct. + * Any and all further callers will reuse that instance. Those then wait for + * a completion signaled at the tail of the CPU stopper callback (1), triggered + * on the end of the Migrate-Disable region (i.e. outermost migrate_enable()). + * + * + * (1) In the cases covered above. There is one more where the completion is + * signaled within affine_move_task() itself: when a subsequent affinity request + * cancels the need for an active migration. Consider: + * + * Initial conditions: P0->cpus_mask = [0, 1] + * + * P0@CPU0 P1 P2 + * + * migrate_disable(); + * <preempted> + * set_cpus_allowed_ptr(P0, [1]); + * <blocks> + * set_cpus_allowed_ptr(P0, [0, 1]); + * <signal completion> + * <awakes> + * + * Note that the above is safe vs a concurrent migrate_enable(), as any + * pending affinity completion is preceded by an uninstallation of + * p->migration_pending done with p->pi_lock held. + */ +static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flags *rf, + int dest_cpu, unsigned int flags) +{ + struct set_affinity_pending my_pending = { }, *pending = NULL; + struct migration_arg arg = { + .task = p, + .dest_cpu = dest_cpu, + }; + bool complete = false; + + /* Can the task run on the task's current CPU? If so, we're done */ + if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) { + struct task_struct *push_task = NULL; + + if ((flags & SCA_MIGRATE_ENABLE) && + (p->migration_flags & MDF_PUSH) && !rq->push_busy) { + rq->push_busy = true; + push_task = get_task_struct(p); + } + + pending = p->migration_pending; + if (pending) { + refcount_inc(&pending->refs); + p->migration_pending = NULL; + complete = true; + } + task_rq_unlock(rq, p, rf); + + if (push_task) { + stop_one_cpu_nowait(rq->cpu, push_cpu_stop, + p, &rq->push_work); + } + + if (complete) + goto do_complete; + + return 0; + } + + if (!(flags & SCA_MIGRATE_ENABLE)) { + /* serialized by p->pi_lock */ + if (!p->migration_pending) { + /* Install the request */ + refcount_set(&my_pending.refs, 1); + init_completion(&my_pending.done); + p->migration_pending = &my_pending; + } else { + pending = p->migration_pending; + refcount_inc(&pending->refs); + } + } + pending = p->migration_pending; + /* + * - !MIGRATE_ENABLE: + * we'll have installed a pending if there wasn't one already. + * + * - MIGRATE_ENABLE: + * we're here because the current CPU isn't matching anymore, + * the only way that can happen is because of a concurrent + * set_cpus_allowed_ptr() call, which should then still be + * pending completion. + * + * Either way, we really should have a @pending here. + */ + if (WARN_ON_ONCE(!pending)) { + task_rq_unlock(rq, p, rf); + return -EINVAL; + } + + if (flags & SCA_MIGRATE_ENABLE) { + + refcount_inc(&pending->refs); /* pending->{arg,stop_work} */ + p->migration_flags &= ~MDF_PUSH; + task_rq_unlock(rq, p, rf); + + pending->arg = (struct migration_arg) { + .task = p, + .dest_cpu = -1, + .pending = pending, + }; + + stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop, + &pending->arg, &pending->stop_work); + + return 0; + } + + if (task_running(rq, p) || p->state == TASK_WAKING) { + /* + * Lessen races (and headaches) by delegating + * is_migration_disabled(p) checks to the stopper, which will + * run on the same CPU as said p. + */ + task_rq_unlock(rq, p, rf); + stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg); + + } else { + + if (!is_migration_disabled(p)) { + if (task_on_rq_queued(p)) + rq = move_queued_task(rq, rf, p, dest_cpu); + + p->migration_pending = NULL; + complete = true; + } + task_rq_unlock(rq, p, rf); + +do_complete: + if (complete) + complete_all(&pending->done); + } + + wait_for_completion(&pending->done); + + if (refcount_dec_and_test(&pending->refs)) + wake_up_var(&pending->refs); + + /* + * Block the original owner of &pending until all subsequent callers + * have seen the completion and decremented the refcount + */ + wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs)); + + return 0; +} + /* * Change a given task's CPU affinity. Migrate the thread to a * proper CPU and schedule it away if the CPU it's executing on @@ -1869,7 +2313,8 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) * call is not atomic; no spinlocks may be held. */ static int __set_cpus_allowed_ptr(struct task_struct *p, - const struct cpumask *new_mask, bool check) + const struct cpumask *new_mask, + u32 flags) { const struct cpumask *cpu_valid_mask = cpu_active_mask; unsigned int dest_cpu; @@ -1880,9 +2325,14 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, rq = task_rq_lock(p, &rf); update_rq_clock(rq); - if (p->flags & PF_KTHREAD) { + if (p->flags & PF_KTHREAD || is_migration_disabled(p)) { /* - * Kernel threads are allowed on online && !active CPUs + * Kernel threads are allowed on online && !active CPUs. + * + * Specifically, migration_disabled() tasks must not fail the + * cpumask_any_and_distribute() pick below, esp. so on + * SCA_MIGRATE_ENABLE, otherwise we'll not call + * set_cpus_allowed_common() and actually reset p->cpus_ptr. */ cpu_valid_mask = cpu_online_mask; } @@ -1891,13 +2341,22 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, * Must re-check here, to close a race against __kthread_bind(), * sched_setaffinity() is not guaranteed to observe the flag. */ - if (check && (p->flags & PF_NO_SETAFFINITY)) { + if ((flags & SCA_CHECK) && (p->flags & PF_NO_SETAFFINITY)) { ret = -EINVAL; goto out; } - if (cpumask_equal(&p->cpus_mask, new_mask)) - goto out; + if (!(flags & SCA_MIGRATE_ENABLE)) { + if (cpumask_equal(&p->cpus_mask, new_mask)) + goto out; + + if (WARN_ON_ONCE(p == current && + is_migration_disabled(p) && + !cpumask_test_cpu(task_cpu(p), new_mask))) { + ret = -EBUSY; + goto out; + } + } /* * Picking a ~random cpu helps in cases where we are changing affinity @@ -1910,7 +2369,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, goto out; } - do_set_cpus_allowed(p, new_mask); + __do_set_cpus_allowed(p, new_mask, flags); if (p->flags & PF_KTHREAD) { /* @@ -1922,23 +2381,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, p->nr_cpus_allowed != 1); } - /* Can the task run on the task's current CPU? If so, we're done */ - if (cpumask_test_cpu(task_cpu(p), new_mask)) - goto out; + return affine_move_task(rq, p, &rf, dest_cpu, flags); - if (task_running(rq, p) || p->state == TASK_WAKING) { - struct migration_arg arg = { p, dest_cpu }; - /* Need help from migration thread: drop lock and wait. */ - task_rq_unlock(rq, p, &rf); - stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg); - return 0; - } else if (task_on_rq_queued(p)) { - /* - * OK, since we're going to drop the lock immediately - * afterwards anyway. - */ - rq = move_queued_task(rq, &rf, p, dest_cpu); - } out: task_rq_unlock(rq, p, &rf); @@ -1947,7 +2391,7 @@ out: int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask) { - return __set_cpus_allowed_ptr(p, new_mask, false); + return __set_cpus_allowed_ptr(p, new_mask, 0); } EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr); @@ -1988,6 +2432,8 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu) * Clearly, migrating tasks to offline CPUs is a fairly daft thing. */ WARN_ON_ONCE(!cpu_online(new_cpu)); + + WARN_ON_ONCE(is_migration_disabled(p)); #endif trace_sched_migrate_task(p, new_cpu); @@ -2318,6 +2764,12 @@ static int select_fallback_rq(int cpu, struct task_struct *p) } fallthrough; case possible: + /* + * XXX When called from select_task_rq() we only + * hold p->pi_lock and again violate locking order. + * + * More yuck to audit. + */ do_set_cpus_allowed(p, cpu_possible_mask); state = fail; break; @@ -2348,12 +2800,12 @@ out: * The caller (fork, wakeup) owns p->pi_lock, ->cpus_ptr is stable. */ static inline -int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags) +int select_task_rq(struct task_struct *p, int cpu, int wake_flags) { lockdep_assert_held(&p->pi_lock); - if (p->nr_cpus_allowed > 1) - cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags); + if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p)) + cpu = p->sched_class->select_task_rq(p, cpu, wake_flags); else cpu = cpumask_any(p->cpus_ptr); @@ -2375,6 +2827,7 @@ int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags) void sched_set_stop_task(int cpu, struct task_struct *stop) { + static struct lock_class_key stop_pi_lock; struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 }; struct task_struct *old_stop = cpu_rq(cpu)->stop; @@ -2390,6 +2843,20 @@ void sched_set_stop_task(int cpu, struct task_struct *stop) sched_setscheduler_nocheck(stop, SCHED_FIFO, ¶m); stop->sched_class = &stop_sched_class; + + /* + * The PI code calls rt_mutex_setprio() with ->pi_lock held to + * adjust the effective priority of a task. As a result, + * rt_mutex_setprio() can trigger (RT) balancing operations, + * which can then trigger wakeups of the stop thread to push + * around the current task. + * + * The stop task itself will never be part of the PI-chain, it + * never blocks, therefore that ->pi_lock recursion is safe. + * Tell lockdep about this by placing the stop->pi_lock in its + * own class. + */ + lockdep_set_class(&stop->pi_lock, &stop_pi_lock); } cpu_rq(cpu)->stop = stop; @@ -2403,15 +2870,23 @@ void sched_set_stop_task(int cpu, struct task_struct *stop) } } -#else +#else /* CONFIG_SMP */ static inline int __set_cpus_allowed_ptr(struct task_struct *p, - const struct cpumask *new_mask, bool check) + const struct cpumask *new_mask, + u32 flags) { return set_cpus_allowed_ptr(p, new_mask); } -#endif /* CONFIG_SMP */ +static inline void migrate_disable_switch(struct rq *rq, struct task_struct *p) { } + +static inline bool rq_has_pinned_tasks(struct rq *rq) +{ + return false; +} + +#endif /* !CONFIG_SMP */ static void ttwu_stat(struct task_struct *p, int cpu, int wake_flags) @@ -2465,7 +2940,7 @@ static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags, #ifdef CONFIG_SMP if (p->sched_class->task_woken) { /* - * Our task @p is fully woken up and running; so its safe to + * Our task @p is fully woken up and running; so it's safe to * drop the rq->lock, hereafter rq is only used for statistics. */ rq_unpin_lock(rq, rf); @@ -2952,7 +3427,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) /* * If the owning (remote) CPU is still in the middle of schedule() with - * this task as prev, wait until its done referencing the task. + * this task as prev, wait until it's done referencing the task. * * Pairs with the smp_store_release() in finish_task(). * @@ -2961,7 +3436,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) */ smp_cond_load_acquire(&p->on_cpu, !VAL); - cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags); + cpu = select_task_rq(p, p->wake_cpu, wake_flags | WF_TTWU); if (task_cpu(p) != cpu) { if (p->in_iowait) { delayacct_blkio_end(p); @@ -3103,6 +3578,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p) init_numa_balancing(clone_flags, p); #ifdef CONFIG_SMP p->wake_entry.u_flags = CSD_TYPE_TTWU; + p->migration_pending = NULL; #endif } @@ -3349,7 +3825,7 @@ void wake_up_new_task(struct task_struct *p) */ p->recent_used_cpu = task_cpu(p); rseq_migrate(p); - __set_task_cpu(p, select_task_rq(p, task_cpu(p), SD_BALANCE_FORK, 0)); + __set_task_cpu(p, select_task_rq(p, task_cpu(p), WF_FORK)); #endif rq = __task_rq_lock(p, &rf); update_rq_clock(rq); @@ -3361,7 +3837,7 @@ void wake_up_new_task(struct task_struct *p) #ifdef CONFIG_SMP if (p->sched_class->task_woken) { /* - * Nothing relies on rq->lock after this, so its fine to + * Nothing relies on rq->lock after this, so it's fine to * drop it. */ rq_unpin_lock(rq, &rf); @@ -3490,6 +3966,90 @@ static inline void finish_task(struct task_struct *prev) #endif } +#ifdef CONFIG_SMP + +static void do_balance_callbacks(struct rq *rq, struct callback_head *head) +{ + void (*func)(struct rq *rq); + struct callback_head *next; + + lockdep_assert_held(&rq->lock); + + while (head) { + func = (void (*)(struct rq *))head->func; + next = head->next; + head->next = NULL; + head = next; + + func(rq); + } +} + +static inline struct callback_head *splice_balance_callbacks(struct rq *rq) +{ + struct callback_head *head = rq->balance_callback; + + lockdep_assert_held(&rq->lock); + if (head) { + rq->balance_callback = NULL; + rq->balance_flags &= ~BALANCE_WORK; + } + + return head; +} + +static void __balance_callbacks(struct rq *rq) +{ + do_balance_callbacks(rq, splice_balance_callbacks(rq)); +} + +static inline void balance_callbacks(struct rq *rq, struct callback_head *head) +{ + unsigned long flags; + + if (unlikely(head)) { + raw_spin_lock_irqsave(&rq->lock, flags); + do_balance_callbacks(rq, head); + raw_spin_unlock_irqrestore(&rq->lock, flags); + } +} + +static void balance_push(struct rq *rq); + +static inline void balance_switch(struct rq *rq) +{ + if (likely(!rq->balance_flags)) + return; + + if (rq->balance_flags & BALANCE_PUSH) { + balance_push(rq); + return; + } + + __balance_callbacks(rq); +} + +#else + +static inline void __balance_callbacks(struct rq *rq) +{ +} + +static inline struct callback_head *splice_balance_callbacks(struct rq *rq) +{ + return NULL; +} + +static inline void balance_callbacks(struct rq *rq, struct callback_head *head) +{ +} + +static inline void balance_switch(struct rq *rq) +{ +} + +#endif + static inline void prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf) { @@ -3515,6 +4075,7 @@ static inline void finish_lock_switch(struct rq *rq) * prev into current: */ spin_acquire(&rq->lock.dep_map, 0, 0, _THIS_IP_); + balance_switch(rq); raw_spin_unlock_irq(&rq->lock); } @@ -3656,43 +4217,6 @@ static struct rq *finish_task_switch(struct task_struct *prev) return rq; } -#ifdef CONFIG_SMP - -/* rq->lock is NOT held, but preemption is disabled */ -static void __balance_callback(struct rq *rq) -{ - struct callback_head *head, *next; - void (*func)(struct rq *rq); - unsigned long flags; - - raw_spin_lock_irqsave(&rq->lock, flags); - head = rq->balance_callback; - rq->balance_callback = NULL; - while (head) { - func = (void (*)(struct rq *))head->func; - next = head->next; - head->next = NULL; - head = next; - - func(rq); - } - raw_spin_unlock_irqrestore(&rq->lock, flags); -} - -static inline void balance_callback(struct rq *rq) -{ - if (unlikely(rq->balance_callback)) - __balance_callback(rq); -} - -#else - -static inline void balance_callback(struct rq *rq) -{ -} - -#endif - /** * schedule_tail - first thing a freshly forked thread must call. * @prev: the thread we just switched away from. @@ -3712,7 +4236,6 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev) */ rq = finish_task_switch(prev); - balance_callback(rq); preempt_enable(); if (current->set_child_tid) @@ -3841,7 +4364,7 @@ unsigned long nr_iowait_cpu(int cpu) } /* - * IO-wait accounting, and how its mostly bollocks (on SMP). + * IO-wait accounting, and how it's mostly bollocks (on SMP). * * The idea behind IO-wait account is to account the idle time that we could * have spend running if it were not for IO. That is, if we were to improve the @@ -3893,7 +4416,7 @@ void sched_exec(void) int dest_cpu; raw_spin_lock_irqsave(&p->pi_lock, flags); - dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), SD_BALANCE_EXEC, 0); + dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), WF_EXEC); if (dest_cpu == smp_processor_id()) goto unlock; @@ -4337,7 +4860,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) /* * Optimization: we know that if all tasks are in the fair class we can * call that function directly, but only if the @prev task wasn't of a - * higher scheduling class, because otherwise those loose the + * higher scheduling class, because otherwise those lose the * opportunity to pull in more work from other CPUs. */ if (likely(prev->sched_class <= &fair_sched_class && @@ -4521,6 +5044,7 @@ static void __sched notrace __schedule(bool preempt) */ ++*switch_count; + migrate_disable_switch(rq, prev); psi_sche |