diff options
author | Thomas Gleixner <tglx@linutronix.de> | 2014-05-22 03:25:54 +0000 |
---|---|---|
committer | Steven Rostedt <rostedt@goodmis.org> | 2016-11-16 14:23:03 -0500 |
commit | b34fcb2f35285229d21e4cce4abb2141e1b64f7c (patch) | |
tree | d327f7006ede1ff73822e5da99805813216d0d41 | |
parent | 91542cf0531c6da3c1e24887a63e42fc7970620f (diff) | |
download | linux-rt-b34fcb2f35285229d21e4cce4abb2141e1b64f7c.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/rtmutex.c
-rw-r--r-- | kernel/rtmutex.c | 57 |
1 files changed, 48 insertions, 9 deletions
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c index 865190821088..5431db127f64 100644 --- a/kernel/rtmutex.c +++ b/kernel/rtmutex.c @@ -273,9 +273,10 @@ 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, @@ -382,9 +383,14 @@ 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->list_entry.prio = task->prio; rt_mutex_enqueue(lock, waiter); @@ -393,6 +399,11 @@ 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; @@ -401,29 +412,48 @@ 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. + */ } /* @@ -436,6 +466,10 @@ 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); @@ -446,6 +480,11 @@ 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; |