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From: Peter Zijlstra <peterz@infradead.org>
Date: Thu, 23 Mar 2017 15:56:14 +0100
Subject: [PATCH 8/9] 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: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas 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: Thomas Gleixner <tglx@linutronix.de>
---
kernel/locking/rtmutex.c | 32 +++++++++++++++++++++++++++++---
1 file changed, 29 insertions(+), 3 deletions(-)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -224,6 +224,12 @@ static inline bool unlock_rt_mutex_safe(
}
#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_wai
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(st
* 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 r
* 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_stru
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;
}
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