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sched/rtmutex: Refactor rt_mutex_setprio()

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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>
This commit is contained in:
Peter Zijlstra 2017-03-23 15:56:11 +01:00 • committed by Thomas Gleixner
parent aa2bfe5536
commit acd58620e4
3 changed files with 91 additions and 111 deletions
Download patch file Download diff file Expand all files Collapse all files

112
kernel/locking/rtmutex.c
View file

@ -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)
static void rt_mutex_adjust_prio(struct task_struct *p)
{
if (!task_has_pi_waiters(p)) {
p->pi_top_task = NULL;
return;
}
struct task_struct *pi_task = NULL;
p->pi_top_task = task_top_pi_waiter(p)->task;
}
lockdep_assert_held(&p->pi_lock);
/*
* 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;
if (task_has_pi_waiters(p))
pi_task = task_top_pi_waiter(p)->task;
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)
{
struct task_struct *top_task = rt_mutex_get_top_task(task);
if (!top_task)
return newprio;
return min(top_task->prio, newprio);
}
/*
* 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() */