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Commit 19830e55 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

rtmutex: Fix more prio comparisons 



There was a pure ->prio comparison left in try_to_wake_rt_mutex(),
convert it to use rt_mutex_waiter_less(), noting that greater-or-equal
is not-less (both in kernel priority view).

This necessitated the introduction of cmp_task() which creates a
pointer to an unnamed stack variable of struct rt_mutex_waiter type to
compare against tasks.

With this, we can now also create and employ rt_mutex_waiter_equal().

Reviewed-and-tested-by: default avatarJuri Lelli <juri.lelli@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
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/20170323150216.455584638@infradead.org


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent e0aad5b4

kernel/locking/rtmutex.c

+29 −3
Original line number Diff line number Diff line
@@ -224,6 +224,12 @@ static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock, 
}

#endif



/*

 * Only use with rt_mutex_waiter_{less,equal}()

 */

#define task_to_waiter(p)	\

	&(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }



static inline int

rt_mutex_waiter_less(struct rt_mutex_waiter *left,

		     struct rt_mutex_waiter *right)
@@ -243,6 +249,25 @@ rt_mutex_waiter_less(struct rt_mutex_waiter *left, 
	return 0;

}



static inline int

rt_mutex_waiter_equal(struct rt_mutex_waiter *left,

		      struct rt_mutex_waiter *right)

{

	if (left->prio != right->prio)

		return 0;



	/*

	 * If both waiters have dl_prio(), we check the deadlines of the

	 * associated tasks.

	 * If left waiter has a dl_prio(), and we didn't return 0 above,

	 * then right waiter has a dl_prio() too.

	 */

	if (dl_prio(left->prio))

		return left->deadline == right->deadline;



	return 1;

}



static void

rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)

{
@@ -553,7 +578,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task, 
	 * enabled we continue, but stop the requeueing in the chain

	 * walk.

	 */

	if (waiter->prio == task->prio && !dl_task(task)) {

	if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {

		if (!detect_deadlock)

			goto out_unlock_pi;

		else
@@ -856,7 +881,8 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task, 
			 * the top waiter priority (kernel view),

			 * @task lost.

			 */

			if (task->prio >= rt_mutex_top_waiter(lock)->prio)

			if (!rt_mutex_waiter_less(task_to_waiter(task),

						  rt_mutex_top_waiter(lock)))

				return 0;



			/*
@@ -1119,7 +1145,7 @@ 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 || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {

		raw_spin_unlock_irqrestore(&task->pi_lock, flags);

		return;

	}