Commit-ID: a57594a13a446d1a6ab1dcd48339f799ce586843
Gitweb: http://git.kernel.org/tip/a57594a13a446d1a6ab1dcd48339f799ce586843
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 22 May 2014 03:25:54 +0000
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Sat, 21 Jun 2014 22:05:30 +0200
rtmutex: Clarify the boost/deboost part
Add a separate local variable for the boost/deboost logic to make the
code more readable. Add comments where appropriate.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
kernel/locking/rtmutex.c | 58 +++++++++++++++++++++++++++++++++++++++---------
1 file changed, 48 insertions(+), 10 deletions(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index cd517091..3e9a759 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -345,9 +345,10 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
struct rt_mutex_waiter *orig_waiter,
struct task_struct *top_task)
{
- struct rt_mutex *lock;
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
+ struct rt_mutex_waiter *prerequeue_top_waiter;
int detect_deadlock, ret = 0, depth = 0;
+ struct rt_mutex *lock;
unsigned long flags;
detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
@@ -454,9 +455,14 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
goto out_unlock_pi;
}
- top_waiter = rt_mutex_top_waiter(lock);
+ /*
+ * Store the current top waiter before doing the requeue
+ * operation on @lock. We need it for the boost/deboost
+ * decision below.
+ */
+ prerequeue_top_waiter = rt_mutex_top_waiter(lock);
- /* Requeue the waiter */
+ /* Requeue the waiter in the lock waiter list. */
rt_mutex_dequeue(lock, waiter);
waiter->prio = task->prio;
rt_mutex_enqueue(lock, waiter);
@@ -465,35 +471,58 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
put_task_struct(task);
+ /*
+ * We must abort the chain walk if there is no lock owner even
+ * in the dead lock detection case, as we have nothing to
+ * follow here. This is the end of the chain we are walking.
+ */
if (!rt_mutex_owner(lock)) {
/*
* If the requeue above changed the top waiter, then we need
* to wake the new top waiter up to try to get the lock.
*/
-
- if (top_waiter != rt_mutex_top_waiter(lock))
+ if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
wake_up_process(rt_mutex_top_waiter(lock)->task);
raw_spin_unlock(&lock->wait_lock);
return 0;
}
- /* Grab the next task */
+ /* Grab the next task, i.e. the owner of @lock */
task = rt_mutex_owner(lock);
get_task_struct(task);
raw_spin_lock_irqsave(&task->pi_lock, flags);
if (waiter == rt_mutex_top_waiter(lock)) {
- /* Boost the owner */
- rt_mutex_dequeue_pi(task, top_waiter);
+ /*
+ * The waiter became the new top (highest priority)
+ * waiter on the lock. Replace the previous top waiter
+ * in the owner tasks pi waiters list with this waiter
+ * and adjust the priority of the owner.
+ */
+ rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);
- } else if (top_waiter == waiter) {
- /* Deboost the owner */
+ } else if (prerequeue_top_waiter == waiter) {
+ /*
+ * The waiter was the top waiter on the lock, but is
+ * no longer the top prority waiter. Replace waiter in
+ * the owner tasks pi waiters list with the new top
+ * (highest priority) waiter and adjust the priority
+ * of the owner.
+ * The new top waiter is stored in @waiter so that
+ * @waiter == @top_waiter evaluates to true below and
+ * we continue to deboost the rest of the chain.
+ */
rt_mutex_dequeue_pi(task, waiter);
waiter = rt_mutex_top_waiter(lock);
rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);
+ } else {
+ /*
+ * Nothing changed. No need to do any priority
+ * adjustment.
+ */
}
/*
@@ -506,6 +535,10 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ /*
+ * Store the top waiter of @lock for the end of chain walk
+ * decision below.
+ */
top_waiter = rt_mutex_top_waiter(lock);
raw_spin_unlock(&lock->wait_lock);
@@ -516,6 +549,11 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
if (!next_lock)
goto out_put_task;
+ /*
+ * If the current waiter is not the top waiter on the lock,
+ * then we can stop the chain walk here if we are not in full
+ * deadlock detection mode.
+ */
if (!detect_deadlock && waiter != top_waiter)
goto out_put_task;
--
To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
|