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authorPeter Zijlstra <peterz@infradead.org>2017-03-23 17:56:11 +0300
committerThomas Gleixner <tglx@linutronix.de>2017-04-04 12:44:06 +0300
commitacd58620e415aee4a43a808d7d2fd87259ee0001 (patch)
treeb0971a53edac32523a6b99b4bd5f15200041634e /kernel/locking/rtmutex.c
parentaa2bfe55366552cb7e93e8709d66e698d79ccc47 (diff)
downloadlinux-acd58620e415aee4a43a808d7d2fd87259ee0001.tar.xz
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>
Diffstat (limited to 'kernel/locking/rtmutex.c')
-rw-r--r--kernel/locking/rtmutex.c112
1 files changed, 30 insertions, 82 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 4b1015ef0dc7..00b49cdbb4e0 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -322,67 +322,16 @@ rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
RB_CLEAR_NODE(&waiter->pi_tree_entry);
}
-/*
- * Must hold both p->pi_lock and task_rq(p)->lock.
- */
-void rt_mutex_update_top_task(struct task_struct *p)
-{
- if (!task_has_pi_waiters(p)) {
- p->pi_top_task = NULL;
- return;
- }
-
- p->pi_top_task = task_top_pi_waiter(p)->task;
-}
-
-/*
- * Calculate task priority from the waiter tree priority
- *
- * Return task->normal_prio when the waiter tree is empty or when
- * the waiter is not allowed to do priority boosting
- */
-int rt_mutex_getprio(struct task_struct *task)
-{
- if (likely(!task_has_pi_waiters(task)))
- return task->normal_prio;
-
- return min(task_top_pi_waiter(task)->prio,
- task->normal_prio);
-}
-
-/*
- * Must hold either p->pi_lock or task_rq(p)->lock.
- */
-struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
-{
- return task->pi_top_task;
-}
-
-/*
- * Called by sched_setscheduler() to get the priority which will be
- * effective after the change.
- */
-int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
+static void rt_mutex_adjust_prio(struct task_struct *p)
{
- struct task_struct *top_task = rt_mutex_get_top_task(task);
+ struct task_struct *pi_task = NULL;
- if (!top_task)
- return newprio;
+ lockdep_assert_held(&p->pi_lock);
- return min(top_task->prio, newprio);
-}
+ if (task_has_pi_waiters(p))
+ pi_task = task_top_pi_waiter(p)->task;
-/*
- * Adjust the priority of a task, after its pi_waiters got modified.
- *
- * This can be both boosting and unboosting. task->pi_lock must be held.
- */
-static void __rt_mutex_adjust_prio(struct task_struct *task)
-{
- int prio = rt_mutex_getprio(task);
-
- if (task->prio != prio || dl_prio(prio))
- rt_mutex_setprio(task, prio);
+ rt_mutex_setprio(p, pi_task);
}
/*
@@ -742,7 +691,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
*/
rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
rt_mutex_enqueue_pi(task, waiter);
- __rt_mutex_adjust_prio(task);
+ rt_mutex_adjust_prio(task);
} else if (prerequeue_top_waiter == waiter) {
/*
@@ -758,7 +707,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
rt_mutex_dequeue_pi(task, waiter);
waiter = rt_mutex_top_waiter(lock);
rt_mutex_enqueue_pi(task, waiter);
- __rt_mutex_adjust_prio(task);
+ rt_mutex_adjust_prio(task);
} else {
/*
* Nothing changed. No need to do any priority
@@ -966,7 +915,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
return -EDEADLK;
raw_spin_lock(&task->pi_lock);
- __rt_mutex_adjust_prio(task);
+ rt_mutex_adjust_prio(task);
waiter->task = task;
waiter->lock = lock;
waiter->prio = task->prio;
@@ -988,7 +937,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
rt_mutex_dequeue_pi(owner, top_waiter);
rt_mutex_enqueue_pi(owner, waiter);
- __rt_mutex_adjust_prio(owner);
+ rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on)
chain_walk = 1;
} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
@@ -1040,13 +989,14 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
waiter = rt_mutex_top_waiter(lock);
/*
- * Remove it from current->pi_waiters. We do not adjust a
- * possible priority boost right now. We execute wakeup in the
- * boosted mode and go back to normal after releasing
- * lock->wait_lock.
+ * Remove it from current->pi_waiters and deboost.
+ *
+ * We must in fact deboost here in order to ensure we call
+ * rt_mutex_setprio() to update p->pi_top_task before the
+ * task unblocks.
*/
rt_mutex_dequeue_pi(current, waiter);
- __rt_mutex_adjust_prio(current);
+ rt_mutex_adjust_prio(current);
/*
* As we are waking up the top waiter, and the waiter stays
@@ -1058,9 +1008,19 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
*/
lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
- raw_spin_unlock(&current->pi_lock);
-
+ /*
+ * We deboosted before waking the top waiter task such that we don't
+ * run two tasks with the 'same' priority (and ensure the
+ * p->pi_top_task pointer points to a blocked task). This however can
+ * lead to priority inversion if we would get preempted after the
+ * deboost but before waking our donor task, hence the preempt_disable()
+ * before unlock.
+ *
+ * Pairs with preempt_enable() in rt_mutex_postunlock();
+ */
+ preempt_disable();
wake_q_add(wake_q, waiter->task);
+ raw_spin_unlock(&current->pi_lock);
}
/*
@@ -1095,7 +1055,7 @@ static void remove_waiter(struct rt_mutex *lock,
if (rt_mutex_has_waiters(lock))
rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
- __rt_mutex_adjust_prio(owner);
+ rt_mutex_adjust_prio(owner);
/* Store the lock on which owner is blocked or NULL */
next_lock = task_blocked_on_lock(owner);
@@ -1134,8 +1094,7 @@ void rt_mutex_adjust_pi(struct task_struct *task)
raw_spin_lock_irqsave(&task->pi_lock, flags);
waiter = task->pi_blocked_on;
- if (!waiter || (waiter->prio == task->prio &&
- !dl_prio(task->prio))) {
+ if (!waiter || (waiter->prio == task->prio && !dl_prio(task->prio))) {
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
return;
}
@@ -1389,17 +1348,6 @@ static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
* Queue the next waiter for wakeup once we release the wait_lock.
*/
mark_wakeup_next_waiter(wake_q, lock);
-
- /*
- * We should deboost before waking the top waiter task such that
- * we don't run two tasks with the 'same' priority. This however
- * can lead to prio-inversion if we would get preempted after
- * the deboost but before waking our high-prio task, hence the
- * preempt_disable before unlock. Pairs with preempt_enable() in
- * rt_mutex_postunlock();
- */
- preempt_disable();
-
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
return true; /* call rt_mutex_postunlock() */