rtmutex: Turn the plist into an rb-tree

Turn the pi-chains from plist to rb-tree, in the rt_mutex code,
and provide a proper comparison function for -deadline and
-priority tasks.

This is done mainly because:
 - classical prio field of the plist is just an int, which might
   not be enough for representing a deadline;
 - manipulating such a list would become O(nr_deadline_tasks),
   which might be to much, as the number of -deadline task increases.

Therefore, an rb-tree is used, and tasks are queued in it according
to the following logic:
 - among two -priority (i.e., SCHED_BATCH/OTHER/RR/FIFO) tasks, the
   one with the higher (lower, actually!) prio wins;
 - among a -priority and a -deadline task, the latter always wins;
 - among two -deadline tasks, the one with the earliest deadline
   wins.

Queueing and dequeueing functions are changed accordingly, for both
the list of a task's pi-waiters and the list of tasks blocked on
a pi-lock.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dario Faggioli <raistlin@linux.it>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-again-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-10-git-send-email-juri.lelli@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 134 insertions, 47 deletions

diff --git a/kernel/locking/rtmutex-debug.c b/kernel/locking/rtmutex-debug.c
index 13b243a323fa..49b2ed3dced8 100644
--- a/kernel/locking/rtmutex-debug.c
+++ b/kernel/locking/rtmutex-debug.c
@@ -24,7 +24,7 @@
 #include <linux/kallsyms.h>
 #include <linux/syscalls.h>
 #include <linux/interrupt.h>
-#include <linux/plist.h>
+#include <linux/rbtree.h>
 #include <linux/fs.h>
 #include <linux/debug_locks.h>
 
@@ -57,7 +57,7 @@ static void printk_lock(struct rt_mutex *lock, int print_owner)
 
 void rt_mutex_debug_task_free(struct task_struct *task)
 {
-        DEBUG_LOCKS_WARN_ON(!plist_head_empty(&task->pi_waiters));
+        DEBUG_LOCKS_WARN_ON(!RB_EMPTY_ROOT(&task->pi_waiters));
         DEBUG_LOCKS_WARN_ON(task->pi_blocked_on);
 }
 
@@ -154,16 +154,12 @@ void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock)
 void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
 {
         memset(waiter, 0x11, sizeof(*waiter));
-        plist_node_init(&waiter->list_entry, MAX_PRIO);
-        plist_node_init(&waiter->pi_list_entry, MAX_PRIO);
         waiter->deadlock_task_pid = NULL;
 }
 
 void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
 {
         put_pid(waiter->deadlock_task_pid);
-        DEBUG_LOCKS_WARN_ON(!plist_node_empty(&waiter->list_entry));
-        DEBUG_LOCKS_WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
         memset(waiter, 0x22, sizeof(*waiter));
 }
 
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 0dd6aec1cb6a..3bf0aa68dd3f 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -14,6 +14,7 @@
 #include <linux/export.h>
 #include <linux/sched.h>
 #include <linux/sched/rt.h>
+#include <linux/sched/deadline.h>
 #include <linux/timer.h>
 
 #include "rtmutex_common.h"
@@ -91,10 +92,104 @@ static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 }
 #endif
 
+static inline int
+rt_mutex_waiter_less(struct rt_mutex_waiter *left,
+                     struct rt_mutex_waiter *right)
+{
+        if (left->task->prio < right->task->prio)
+                return 1;
+
+        /*
+         * If both tasks are dl_task(), we check their deadlines.
+         */
+        if (dl_prio(left->task->prio) && dl_prio(right->task->prio))
+                return (left->task->dl.deadline < right->task->dl.deadline);
+
+        return 0;
+}
+
+static void
+rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
+{
+        struct rb_node **link = &lock->waiters.rb_node;
+        struct rb_node *parent = NULL;
+        struct rt_mutex_waiter *entry;
+        int leftmost = 1;
+
+        while (*link) {
+                parent = *link;
+                entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
+                if (rt_mutex_waiter_less(waiter, entry)) {
+                        link = &parent->rb_left;
+                } else {
+                        link = &parent->rb_right;
+                        leftmost = 0;
+                }
+        }
+
+        if (leftmost)
+                lock->waiters_leftmost = &waiter->tree_entry;
+
+        rb_link_node(&waiter->tree_entry, parent, link);
+        rb_insert_color(&waiter->tree_entry, &lock->waiters);
+}
+
+static void
+rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
+{
+        if (RB_EMPTY_NODE(&waiter->tree_entry))
+                return;
+
+        if (lock->waiters_leftmost == &waiter->tree_entry)
+                lock->waiters_leftmost = rb_next(&waiter->tree_entry);
+
+        rb_erase(&waiter->tree_entry, &lock->waiters);
+        RB_CLEAR_NODE(&waiter->tree_entry);
+}
+
+static void
+rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
+{
+        struct rb_node **link = &task->pi_waiters.rb_node;
+        struct rb_node *parent = NULL;
+        struct rt_mutex_waiter *entry;
+        int leftmost = 1;
+
+        while (*link) {
+                parent = *link;
+                entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
+                if (rt_mutex_waiter_less(waiter, entry)) {
+                        link = &parent->rb_left;
+                } else {
+                        link = &parent->rb_right;
+                        leftmost = 0;
+                }
+        }
+
+        if (leftmost)
+                task->pi_waiters_leftmost = &waiter->pi_tree_entry;
+
+        rb_link_node(&waiter->pi_tree_entry, parent, link);
+        rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
+}
+
+static void
+rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
+{
+        if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
+                return;
+
+        if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
+                task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
+
+        rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
+        RB_CLEAR_NODE(&waiter->pi_tree_entry);
+}
+
 /*
- * Calculate task priority from the waiter list priority
+ * Calculate task priority from the waiter tree priority
  *
- * Return task->normal_prio when the waiter list is empty or when
+ * Return task->normal_prio when the waiter tree is empty or when
  * the waiter is not allowed to do priority boosting
  */
 int rt_mutex_getprio(struct task_struct *task)
@@ -102,7 +197,7 @@ int rt_mutex_getprio(struct task_struct *task)
         if (likely(!task_has_pi_waiters(task)))
                 return task->normal_prio;
 
-        return min(task_top_pi_waiter(task)->pi_list_entry.prio,
+        return min(task_top_pi_waiter(task)->task->prio,
                    task->normal_prio);
 }
 
@@ -233,7 +328,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
          * When deadlock detection is off then we check, if further
          * priority adjustment is necessary.
          */
-        if (!detect_deadlock && waiter->list_entry.prio == task->prio)
+        if (!detect_deadlock && waiter->task->prio == task->prio)
                 goto out_unlock_pi;
 
         lock = waiter->lock;
@@ -254,9 +349,9 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
         top_waiter = rt_mutex_top_waiter(lock);
 
         /* Requeue the waiter */
-        plist_del(&waiter->list_entry, &lock->wait_list);
-        waiter->list_entry.prio = task->prio;
-        plist_add(&waiter->list_entry, &lock->wait_list);
+        rt_mutex_dequeue(lock, waiter);
+        waiter->task->prio = task->prio;
+        rt_mutex_enqueue(lock, waiter);
 
         /* Release the task */
         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
@@ -280,17 +375,15 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 
         if (waiter == rt_mutex_top_waiter(lock)) {
                 /* Boost the owner */
-                plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
-                waiter->pi_list_entry.prio = waiter->list_entry.prio;
-                plist_add(&waiter->pi_list_entry, &task->pi_waiters);
+                rt_mutex_dequeue_pi(task, top_waiter);
+                rt_mutex_enqueue_pi(task, waiter);
                 __rt_mutex_adjust_prio(task);
 
         } else if (top_waiter == waiter) {
                 /* Deboost the owner */
-                plist_del(&waiter->pi_list_entry, &task->pi_waiters);
+                rt_mutex_dequeue_pi(task, waiter);
                 waiter = rt_mutex_top_waiter(lock);
-                waiter->pi_list_entry.prio = waiter->list_entry.prio;
-                plist_add(&waiter->pi_list_entry, &task->pi_waiters);
+                rt_mutex_enqueue_pi(task, waiter);
                 __rt_mutex_adjust_prio(task);
         }
 
@@ -355,7 +448,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
          * 3) it is top waiter
          */
         if (rt_mutex_has_waiters(lock)) {
-                if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) {
+                if (task->prio >= rt_mutex_top_waiter(lock)->task->prio) {
                         if (!waiter || waiter != rt_mutex_top_waiter(lock))
                                 return 0;
                 }
@@ -369,7 +462,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 
                 /* remove the queued waiter. */
                 if (waiter) {
-                        plist_del(&waiter->list_entry, &lock->wait_list);
+                        rt_mutex_dequeue(lock, waiter);
                         task->pi_blocked_on = NULL;
                 }
 
@@ -379,8 +472,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
                  */
                 if (rt_mutex_has_waiters(lock)) {
                         top = rt_mutex_top_waiter(lock);
-                        top->pi_list_entry.prio = top->list_entry.prio;
-                        plist_add(&top->pi_list_entry, &task->pi_waiters);
+                        rt_mutex_enqueue_pi(task, top);
                 }
                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
         }
@@ -416,13 +508,11 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
         __rt_mutex_adjust_prio(task);
         waiter->task = task;
         waiter->lock = lock;
-        plist_node_init(&waiter->list_entry, task->prio);
-        plist_node_init(&waiter->pi_list_entry, task->prio);
 
         /* Get the top priority waiter on the lock */
         if (rt_mutex_has_waiters(lock))
                 top_waiter = rt_mutex_top_waiter(lock);
-        plist_add(&waiter->list_entry, &lock->wait_list);
+        rt_mutex_enqueue(lock, waiter);
 
         task->pi_blocked_on = waiter;
 
@@ -433,8 +523,8 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 
         if (waiter == rt_mutex_top_waiter(lock)) {
                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
-                plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
-                plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
+                rt_mutex_dequeue_pi(owner, top_waiter);
+                rt_mutex_enqueue_pi(owner, waiter);
 
                 __rt_mutex_adjust_prio(owner);
                 if (owner->pi_blocked_on)
@@ -486,7 +576,7 @@ static void wakeup_next_waiter(struct rt_mutex *lock)
          * boosted mode and go back to normal after releasing
          * lock->wait_lock.
          */
-        plist_del(&waiter->pi_list_entry, &current->pi_waiters);
+        rt_mutex_dequeue_pi(current, waiter);
 
         rt_mutex_set_owner(lock, NULL);
 
@@ -510,7 +600,7 @@ static void remove_waiter(struct rt_mutex *lock,
         int chain_walk = 0;
 
         raw_spin_lock_irqsave(&current->pi_lock, flags);
-        plist_del(&waiter->list_entry, &lock->wait_list);
+        rt_mutex_dequeue(lock, waiter);
         current->pi_blocked_on = NULL;
         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 
@@ -521,13 +611,13 @@ static void remove_waiter(struct rt_mutex *lock,
 
                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 
-                plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
+                rt_mutex_dequeue_pi(owner, waiter);
 
                 if (rt_mutex_has_waiters(lock)) {
                         struct rt_mutex_waiter *next;
 
                         next = rt_mutex_top_waiter(lock);
-                        plist_add(&next->pi_list_entry, &owner->pi_waiters);
+                        rt_mutex_enqueue_pi(owner, next);
                 }
                 __rt_mutex_adjust_prio(owner);
 
@@ -537,8 +627,6 @@ static void remove_waiter(struct rt_mutex *lock,
                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
         }
 
-        WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
-
         if (!chain_walk)
                 return;
 
@@ -565,7 +653,7 @@ void rt_mutex_adjust_pi(struct task_struct *task)
         raw_spin_lock_irqsave(&task->pi_lock, flags);
 
         waiter = task->pi_blocked_on;
-        if (!waiter || waiter->list_entry.prio == task->prio) {
+        if (!waiter || waiter->task->prio == task->prio) {
                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
                 return;
         }
@@ -638,6 +726,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
         int ret = 0;
 
         debug_rt_mutex_init_waiter(&waiter);
+        RB_CLEAR_NODE(&waiter.pi_tree_entry);
+        RB_CLEAR_NODE(&waiter.tree_entry);
 
         raw_spin_lock(&lock->wait_lock);
 
@@ -904,7 +994,8 @@ void __rt_mutex_init(struct rt_mutex *lock, const char *name)
 {
         lock->owner = NULL;
         raw_spin_lock_init(&lock->wait_lock);
-        plist_head_init(&lock->wait_list);
+        lock->waiters = RB_ROOT;
+        lock->waiters_leftmost = NULL;
 
         debug_rt_mutex_init(lock, name);
 }
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 53a66c85261b..b65442fe5ade 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -40,13 +40,13 @@ extern void schedule_rt_mutex_test(struct rt_mutex *lock);
  * This is the control structure for tasks blocked on a rt_mutex,
  * which is allocated on the kernel stack on of the blocked task.
  *
- * @list_entry:         pi node to enqueue into the mutex waiters list
- * @pi_list_entry:      pi node to enqueue into the mutex owner waiters list
+ * @tree_entry:         pi node to enqueue into the mutex waiters tree
+ * @pi_tree_entry:      pi node to enqueue into the mutex owner waiters tree
  * @task:               task reference to the blocked task
  */
 struct rt_mutex_waiter {
-        struct plist_node       list_entry;
-        struct plist_node       pi_list_entry;
+        struct rb_node          tree_entry;
+        struct rb_node          pi_tree_entry;
         struct task_struct      *task;
         struct rt_mutex         *lock;
 #ifdef CONFIG_DEBUG_RT_MUTEXES
@@ -57,11 +57,11 @@ struct rt_mutex_waiter {
 };
 
 /*
- * Various helpers to access the waiters-plist:
+ * Various helpers to access the waiters-tree:
  */
 static inline int rt_mutex_has_waiters(struct rt_mutex *lock)
 {
-        return !plist_head_empty(&lock->wait_list);
+        return !RB_EMPTY_ROOT(&lock->waiters);
 }
 
 static inline struct rt_mutex_waiter *
@@ -69,8 +69,8 @@ rt_mutex_top_waiter(struct rt_mutex *lock)
 {
         struct rt_mutex_waiter *w;
 
-        w = plist_first_entry(&lock->wait_list, struct rt_mutex_waiter,
-                               list_entry);
+        w = rb_entry(lock->waiters_leftmost, struct rt_mutex_waiter,
+                     tree_entry);
         BUG_ON(w->lock != lock);
 
         return w;
@@ -78,14 +78,14 @@ rt_mutex_top_waiter(struct rt_mutex *lock)
 
 static inline int task_has_pi_waiters(struct task_struct *p)
 {
-        return !plist_head_empty(&p->pi_waiters);
+        return !RB_EMPTY_ROOT(&p->pi_waiters);
 }
 
 static inline struct rt_mutex_waiter *
 task_top_pi_waiter(struct task_struct *p)
 {
-        return plist_first_entry(&p->pi_waiters, struct rt_mutex_waiter,
-                                  pi_list_entry);
+        return rb_entry(p->pi_waiters_leftmost, struct rt_mutex_waiter,
+                        pi_tree_entry);
 }
 
 /*