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authorThomas Gleixner <tglx@linutronix.de>2014-05-22 03:25:57 +0000
committerAnders Roxell <anders.roxell@linaro.org>2015-06-01 12:03:33 +0200
commit011af1d97ff4114bccfb89a42f2ef2b7e614c118 (patch)
tree0e4651352449d5989308288708898a30eb361ead
parenta4039564aa89495d06b14046250f3eea5aea7faf (diff)
downloadlinux-linaro-stable-011af1d97ff4114bccfb89a42f2ef2b7e614c118.tar.gz
rtmutex: Avoid pointless requeueing in the deadlock detection chain walk
upstream commit: 67792e2cabadbadd1a93f6790fa7bcbd47eca7c3 In case the dead lock detector is enabled we follow the lock chain to the end in rt_mutex_adjust_prio_chain, even if we could stop earlier due to the priority/waiter constellation. But once we are no longer the top priority waiter in a certain step or the task holding the lock has already the same priority then there is no point in dequeing and enqueing along the lock chain as there is no change at all. So stop the queueing at this point. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Link: http://lkml.kernel.org/r/20140522031950.280830190@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
-rw-r--r--kernel/locking/rtmutex.c77
1 files changed, 70 insertions, 7 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 07fb4d717039..a0d9eadcfe02 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -440,6 +440,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
struct rt_mutex *lock;
bool detect_deadlock;
unsigned long flags;
+ bool requeue = true;
detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
@@ -529,18 +530,31 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
goto out_unlock_pi;
/*
* If deadlock detection is off, we stop here if we
- * are not the top pi waiter of the task.
+ * are not the top pi waiter of the task. If deadlock
+ * detection is enabled we continue, but stop the
+ * requeueing in the chain walk.
*/
- if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
- goto out_unlock_pi;
+ if (top_waiter != task_top_pi_waiter(task)) {
+ if (!detect_deadlock)
+ goto out_unlock_pi;
+ else
+ requeue = false;
+ }
}
/*
- * When deadlock detection is off then we check, if further
- * priority adjustment is necessary.
+ * If the waiter priority is the same as the task priority
+ * then there is no further priority adjustment necessary. If
+ * deadlock detection is off, we stop the chain walk. If its
+ * enabled we continue, but stop the requeueing in the chain
+ * walk.
*/
- if (!detect_deadlock && waiter->prio == task->prio)
- goto out_unlock_pi;
+ if (waiter->prio == task->prio) {
+ if (!detect_deadlock)
+ goto out_unlock_pi;
+ else
+ requeue = false;
+ }
/*
* [4] Get the next lock
@@ -574,6 +588,55 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
}
/*
+ * If we just follow the lock chain for deadlock detection, no
+ * need to do all the requeue operations. To avoid a truckload
+ * of conditionals around the various places below, just do the
+ * minimum chain walk checks.
+ */
+ if (!requeue) {
+ /*
+ * No requeue[7] here. Just release @task [8]
+ */
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ put_task_struct(task);
+
+ /*
+ * [9] check_exit_conditions_3 protected by lock->wait_lock.
+ * If there is no owner of the lock, end of chain.
+ */
+ if (!rt_mutex_owner(lock)) {
+ raw_spin_unlock(&lock->wait_lock);
+ return 0;
+ }
+
+ /* [10] Grab the next task, i.e. owner of @lock */
+ task = rt_mutex_owner(lock);
+ get_task_struct(task);
+ raw_spin_lock_irqsave(&task->pi_lock, flags);
+
+ /*
+ * No requeue [11] here. We just do deadlock detection.
+ *
+ * [12] Store whether owner is blocked
+ * itself. Decision is made after dropping the locks
+ */
+ next_lock = task_blocked_on_lock(task);
+ /*
+ * Get the top waiter for the next iteration
+ */
+ top_waiter = rt_mutex_top_waiter(lock);
+
+ /* [13] Drop locks */
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+ raw_spin_unlock(&lock->wait_lock);
+
+ /* If owner is not blocked, end of chain. */
+ if (!next_lock)
+ goto out_put_task;
+ goto again;
+ }
+
+ /*
* Store the current top waiter before doing the requeue
* operation on @lock. We need it for the boost/deboost
* decision below.