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authorThomas Gleixner <tglx@linutronix.de>2014-05-22 03:25:54 +0000
committerAnders Roxell <anders.roxell@linaro.org>2015-06-01 12:03:32 +0200
commit9b24b11f5b4d7d0a37b7b45fa48b4a00e9587879 (patch)
tree2958a4db925ca07afcf8f655af86ad115b96768d
parent66147569ce90e0c4b9ce8b90e2dc7c37da999c6c (diff)
downloadlinux-linaro-stable-9b24b11f5b4d7d0a37b7b45fa48b4a00e9587879.tar.gz
rtmutex: Clarify the boost/deboost part
upstream commit: a57594a13a446d1a6ab1dcd48339f799ce586843 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@linutronix.de> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Conflicts: kernel/locking/rtmutex.c
-rw-r--r--kernel/locking/rtmutex.c57
1 files changed, 48 insertions, 9 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 901a29345451..85f5369e27f3 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -366,9 +366,10 @@ 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,
@@ -475,9 +476,14 @@ 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);
@@ -486,6 +492,11 @@ 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)) {
struct rt_mutex_waiter *lock_top_waiter;
@@ -494,29 +505,48 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
* to wake the new top waiter up to try to get the lock.
*/
lock_top_waiter = rt_mutex_top_waiter(lock);
- if (top_waiter != lock_top_waiter)
+ if (prerequeue_top_waiter != lock_top_waiter)
rt_mutex_wake_waiter(lock_top_waiter);
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.
+ */
}
/*
@@ -529,6 +559,10 @@ 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);
@@ -539,6 +573,11 @@ 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;