sched/rtmutex: Refactor rt_mutex_setprio()
With the introduction of SCHED_DEADLINE the whole notion that priority is a single number is gone, therefore the @prio argument to rt_mutex_setprio() doesn't make sense anymore. So rework the code to pass a pi_task instead. Note this also fixes a problem with pi_top_task caching; previously we would not set the pointer (call rt_mutex_update_top_task) if the priority didn't change, this could lead to a stale pointer. As for the XXX, I think its fine to use pi_task->prio, because if it differs from waiter->prio, a PI chain update is immenent. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: juri.lelli@arm.com Cc: bigeasy@linutronix.de Cc: xlpang@redhat.com Cc: rostedt@goodmis.org Cc: mathieu.desnoyers@efficios.com Cc: jdesfossez@efficios.com Cc: bristot@redhat.com Link: http://lkml.kernel.org/r/20170323150216.303827095@infradead.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -18,28 +18,20 @@ static inline int rt_task(struct task_struct *p)
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}
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#ifdef CONFIG_RT_MUTEXES
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extern int rt_mutex_getprio(struct task_struct *p);
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extern void rt_mutex_setprio(struct task_struct *p, int prio);
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extern int rt_mutex_get_effective_prio(struct task_struct *task, int newprio);
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extern void rt_mutex_update_top_task(struct task_struct *p);
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extern struct task_struct *rt_mutex_get_top_task(struct task_struct *task);
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/*
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* Must hold either p->pi_lock or task_rq(p)->lock.
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*/
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static inline struct task_struct *rt_mutex_get_top_task(struct task_struct *p)
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{
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return p->pi_top_task;
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}
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extern void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task);
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extern void rt_mutex_adjust_pi(struct task_struct *p);
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static inline bool tsk_is_pi_blocked(struct task_struct *tsk)
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{
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return tsk->pi_blocked_on != NULL;
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}
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#else
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static inline int rt_mutex_getprio(struct task_struct *p)
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{
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return p->normal_prio;
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}
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static inline int rt_mutex_get_effective_prio(struct task_struct *task,
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int newprio)
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{
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return newprio;
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}
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static inline struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
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{
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return NULL;
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@ -322,67 +322,16 @@ rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
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RB_CLEAR_NODE(&waiter->pi_tree_entry);
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}
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/*
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* Must hold both p->pi_lock and task_rq(p)->lock.
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*/
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void rt_mutex_update_top_task(struct task_struct *p)
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static void rt_mutex_adjust_prio(struct task_struct *p)
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{
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if (!task_has_pi_waiters(p)) {
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p->pi_top_task = NULL;
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return;
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}
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struct task_struct *pi_task = NULL;
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p->pi_top_task = task_top_pi_waiter(p)->task;
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}
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lockdep_assert_held(&p->pi_lock);
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/*
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* Calculate task priority from the waiter tree priority
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*
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* Return task->normal_prio when the waiter tree is empty or when
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* the waiter is not allowed to do priority boosting
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*/
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int rt_mutex_getprio(struct task_struct *task)
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{
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if (likely(!task_has_pi_waiters(task)))
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return task->normal_prio;
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if (task_has_pi_waiters(p))
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pi_task = task_top_pi_waiter(p)->task;
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return min(task_top_pi_waiter(task)->prio,
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task->normal_prio);
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}
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/*
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* Must hold either p->pi_lock or task_rq(p)->lock.
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*/
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struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
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{
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return task->pi_top_task;
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}
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/*
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* Called by sched_setscheduler() to get the priority which will be
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* effective after the change.
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*/
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int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
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{
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struct task_struct *top_task = rt_mutex_get_top_task(task);
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if (!top_task)
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return newprio;
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return min(top_task->prio, newprio);
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}
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/*
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* Adjust the priority of a task, after its pi_waiters got modified.
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*
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* This can be both boosting and unboosting. task->pi_lock must be held.
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*/
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static void __rt_mutex_adjust_prio(struct task_struct *task)
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{
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int prio = rt_mutex_getprio(task);
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if (task->prio != prio || dl_prio(prio))
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rt_mutex_setprio(task, prio);
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rt_mutex_setprio(p, pi_task);
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}
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/*
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@ -742,7 +691,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
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*/
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rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
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rt_mutex_enqueue_pi(task, waiter);
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__rt_mutex_adjust_prio(task);
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rt_mutex_adjust_prio(task);
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} else if (prerequeue_top_waiter == waiter) {
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/*
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@ -758,7 +707,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
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rt_mutex_dequeue_pi(task, waiter);
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waiter = rt_mutex_top_waiter(lock);
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rt_mutex_enqueue_pi(task, waiter);
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__rt_mutex_adjust_prio(task);
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rt_mutex_adjust_prio(task);
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} else {
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/*
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* Nothing changed. No need to do any priority
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@ -966,7 +915,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
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return -EDEADLK;
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raw_spin_lock(&task->pi_lock);
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__rt_mutex_adjust_prio(task);
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rt_mutex_adjust_prio(task);
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waiter->task = task;
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waiter->lock = lock;
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waiter->prio = task->prio;
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@ -988,7 +937,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
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rt_mutex_dequeue_pi(owner, top_waiter);
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rt_mutex_enqueue_pi(owner, waiter);
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__rt_mutex_adjust_prio(owner);
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rt_mutex_adjust_prio(owner);
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if (owner->pi_blocked_on)
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chain_walk = 1;
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} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
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@ -1040,13 +989,14 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
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waiter = rt_mutex_top_waiter(lock);
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/*
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* Remove it from current->pi_waiters. We do not adjust a
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* possible priority boost right now. We execute wakeup in the
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* boosted mode and go back to normal after releasing
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* lock->wait_lock.
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* Remove it from current->pi_waiters and deboost.
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*
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* We must in fact deboost here in order to ensure we call
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* rt_mutex_setprio() to update p->pi_top_task before the
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* task unblocks.
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*/
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rt_mutex_dequeue_pi(current, waiter);
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__rt_mutex_adjust_prio(current);
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rt_mutex_adjust_prio(current);
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/*
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* As we are waking up the top waiter, and the waiter stays
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@ -1058,9 +1008,19 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
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*/
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lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
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raw_spin_unlock(¤t->pi_lock);
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/*
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* We deboosted before waking the top waiter task such that we don't
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* run two tasks with the 'same' priority (and ensure the
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* p->pi_top_task pointer points to a blocked task). This however can
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* lead to priority inversion if we would get preempted after the
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* deboost but before waking our donor task, hence the preempt_disable()
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* before unlock.
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*
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* Pairs with preempt_enable() in rt_mutex_postunlock();
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*/
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preempt_disable();
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wake_q_add(wake_q, waiter->task);
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raw_spin_unlock(¤t->pi_lock);
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}
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/*
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@ -1095,7 +1055,7 @@ static void remove_waiter(struct rt_mutex *lock,
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if (rt_mutex_has_waiters(lock))
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rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
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__rt_mutex_adjust_prio(owner);
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rt_mutex_adjust_prio(owner);
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/* Store the lock on which owner is blocked or NULL */
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next_lock = task_blocked_on_lock(owner);
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@ -1134,8 +1094,7 @@ void rt_mutex_adjust_pi(struct task_struct *task)
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raw_spin_lock_irqsave(&task->pi_lock, flags);
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waiter = task->pi_blocked_on;
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if (!waiter || (waiter->prio == task->prio &&
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!dl_prio(task->prio))) {
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if (!waiter || (waiter->prio == task->prio && !dl_prio(task->prio))) {
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raw_spin_unlock_irqrestore(&task->pi_lock, flags);
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return;
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}
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@ -1389,17 +1348,6 @@ static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
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* Queue the next waiter for wakeup once we release the wait_lock.
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*/
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mark_wakeup_next_waiter(wake_q, lock);
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/*
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* We should deboost before waking the top waiter task such that
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* we don't run two tasks with the 'same' priority. This however
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* can lead to prio-inversion if we would get preempted after
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* the deboost but before waking our high-prio task, hence the
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* preempt_disable before unlock. Pairs with preempt_enable() in
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* rt_mutex_postunlock();
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*/
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preempt_disable();
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raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
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return true; /* call rt_mutex_postunlock() */
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@ -3671,10 +3671,25 @@ EXPORT_SYMBOL(default_wake_function);
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#ifdef CONFIG_RT_MUTEXES
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static inline int __rt_effective_prio(struct task_struct *pi_task, int prio)
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{
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if (pi_task)
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prio = min(prio, pi_task->prio);
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return prio;
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}
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static inline int rt_effective_prio(struct task_struct *p, int prio)
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{
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struct task_struct *pi_task = rt_mutex_get_top_task(p);
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return __rt_effective_prio(pi_task, prio);
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}
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/*
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* rt_mutex_setprio - set the current priority of a task
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* @p: task
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* @prio: prio value (kernel-internal form)
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* @p: task to boost
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* @pi_task: donor task
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*
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* This function changes the 'effective' priority of a task. It does
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* not touch ->normal_prio like __setscheduler().
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* Used by the rt_mutex code to implement priority inheritance
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* logic. Call site only calls if the priority of the task changed.
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*/
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void rt_mutex_setprio(struct task_struct *p, int prio)
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void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
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{
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int oldprio, queued, running, queue_flag =
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int prio, oldprio, queued, running, queue_flag =
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DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
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const struct sched_class *prev_class;
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struct rq_flags rf;
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struct rq *rq;
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BUG_ON(prio > MAX_PRIO);
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/* XXX used to be waiter->prio, not waiter->task->prio */
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prio = __rt_effective_prio(pi_task, p->normal_prio);
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/*
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* If nothing changed; bail early.
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*/
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if (p->pi_top_task == pi_task && prio == p->prio && !dl_prio(prio))
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return;
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rq = __task_rq_lock(p, &rf);
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update_rq_clock(rq);
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/*
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* Set under pi_lock && rq->lock, such that the value can be used under
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* either lock.
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*
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* Note that there is loads of tricky to make this pointer cache work
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* right. rt_mutex_slowunlock()+rt_mutex_postunlock() work together to
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* ensure a task is de-boosted (pi_task is set to NULL) before the
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* task is allowed to run again (and can exit). This ensures the pointer
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* points to a blocked task -- which guaratees the task is present.
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*/
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p->pi_top_task = pi_task;
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/*
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* For FIFO/RR we only need to set prio, if that matches we're done.
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*/
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if (prio == p->prio && !dl_prio(prio))
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goto out_unlock;
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/*
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* Idle task boosting is a nono in general. There is one
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goto out_unlock;
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}
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rt_mutex_update_top_task(p);
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trace_sched_pi_setprio(p, prio);
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trace_sched_pi_setprio(p, prio); /* broken */
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oldprio = p->prio;
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if (oldprio == prio)
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* running task
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*/
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if (dl_prio(prio)) {
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struct task_struct *pi_task = rt_mutex_get_top_task(p);
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if (!dl_prio(p->normal_prio) ||
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(pi_task && dl_entity_preempt(&pi_task->dl, &p->dl))) {
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p->dl.dl_boosted = 1;
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balance_callback(rq);
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preempt_enable();
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}
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#else
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static inline int rt_effective_prio(struct task_struct *p, int prio)
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{
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return prio;
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}
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#endif
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void set_user_nice(struct task_struct *p, long nice)
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* Keep a potential priority boosting if called from
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* sched_setscheduler().
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*/
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p->prio = normal_prio(p);
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if (keep_boost)
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p->prio = rt_mutex_get_effective_prio(p, normal_prio(p));
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else
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p->prio = normal_prio(p);
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p->prio = rt_effective_prio(p, p->prio);
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if (dl_prio(p->prio))
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p->sched_class = &dl_sched_class;
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* the runqueue. This will be done when the task deboost
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* itself.
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*/
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new_effective_prio = rt_mutex_get_effective_prio(p, newprio);
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new_effective_prio = rt_effective_prio(p, newprio);
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if (new_effective_prio == oldprio)
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queue_flags &= ~DEQUEUE_MOVE;
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}
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