locking/rtmutex: replace top-waiter and pi_waiters leftmost caching

... with the generic rbtree flavor instead. No changes
in semantics whatsoever.

Link: http://lkml.kernel.org/r/20170719014603.19029-10-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

7 files changed, 27 insertions, 44 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 0e849715e5be..3c07ace5b431 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -175,9 +175,8 @@ extern struct cred init_cred;
 
 #ifdef CONFIG_RT_MUTEXES
 # define INIT_RT_MUTEXES(tsk)                                           \
-        .pi_waiters = RB_ROOT,                                          \
-        .pi_top_task = NULL,                                            \
-        .pi_waiters_leftmost = NULL,
+        .pi_waiters = RB_ROOT_CACHED,                                   \
+        .pi_top_task = NULL,
 #else
 # define INIT_RT_MUTEXES(tsk)
 #endif
diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
index 44fd002f7cd5..53fcbe9de7fd 100644
--- a/include/linux/rtmutex.h
+++ b/include/linux/rtmutex.h
@@ -22,18 +22,17 @@ extern int max_lock_depth; /* for sysctl */
  * The rt_mutex structure
  *
  * @wait_lock:  spinlock to protect the structure
- * @waiters:    rbtree root to enqueue waiters in priority order
- * @waiters_leftmost: top waiter
+ * @waiters:    rbtree root to enqueue waiters in priority order;
+ *              caches top-waiter (leftmost node).
  * @owner:      the mutex owner
  */
 struct rt_mutex {
         raw_spinlock_t          wait_lock;
-        struct rb_root          waiters;
-        struct rb_node          *waiters_leftmost;
+        struct rb_root_cached   waiters;
         struct task_struct      *owner;
 #ifdef CONFIG_DEBUG_RT_MUTEXES
         int                     save_state;
-        const char              *name, *file;
+        const char              *name, *file;
         int                     line;
         void                    *magic;
 #endif
@@ -84,7 +83,7 @@ do { \
 
 #define __RT_MUTEX_INITIALIZER(mutexname) \
         { .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(mutexname.wait_lock) \
-        , .waiters = RB_ROOT \
+        , .waiters = RB_ROOT_CACHED \
         , .owner = NULL \
         __DEBUG_RT_MUTEX_INITIALIZER(mutexname) \
         __DEP_MAP_RT_MUTEX_INITIALIZER(mutexname)}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 68b38335d33c..92fb8dd5a9e4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -812,8 +812,7 @@ struct task_struct {
 
 #ifdef CONFIG_RT_MUTEXES
         /* PI waiters blocked on a rt_mutex held by this task: */
-        struct rb_root                  pi_waiters;
-        struct rb_node                  *pi_waiters_leftmost;
+        struct rb_root_cached           pi_waiters;
         /* Updated under owner's pi_lock and rq lock */
         struct task_struct              *pi_top_task;
         /* Deadlock detection and priority inheritance handling: */
diff --git a/kernel/fork.c b/kernel/fork.c
index 2ccbbbfcb7b8..6f1b0af00bda 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1462,8 +1462,7 @@ static void rt_mutex_init_task(struct task_struct *p)
 {
         raw_spin_lock_init(&p->pi_lock);
 #ifdef CONFIG_RT_MUTEXES
-        p->pi_waiters = RB_ROOT;
-        p->pi_waiters_leftmost = NULL;
+        p->pi_waiters = RB_ROOT_CACHED;
         p->pi_top_task = NULL;
         p->pi_blocked_on = NULL;
 #endif
diff --git a/kernel/locking/rtmutex-debug.c b/kernel/locking/rtmutex-debug.c
index ac35e648b0e5..f4a74e78d467 100644
--- a/kernel/locking/rtmutex-debug.c
+++ b/kernel/locking/rtmutex-debug.c
@@ -58,7 +58,7 @@ 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(!RB_EMPTY_ROOT(&task->pi_waiters));
+        DEBUG_LOCKS_WARN_ON(!RB_EMPTY_ROOT(&task->pi_waiters.rb_root));
         DEBUG_LOCKS_WARN_ON(task->pi_blocked_on);
 }
 
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 649dc9d3951a..6f3dba6e4e9e 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -271,10 +271,10 @@ rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
 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 **link = &lock->waiters.rb_root.rb_node;
         struct rb_node *parent = NULL;
         struct rt_mutex_waiter *entry;
-        int leftmost = 1;
+        bool leftmost = true;
 
         while (*link) {
                 parent = *link;
@@ -283,15 +283,12 @@ rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
                         link = &parent->rb_left;
                 } else {
                         link = &parent->rb_right;
-                        leftmost = 0;
+                        leftmost = false;
                 }
         }
 
-        if (leftmost)
-                lock->waiters_leftmost = &waiter->tree_entry;
-
         rb_link_node(&waiter->tree_entry, parent, link);
-        rb_insert_color(&waiter->tree_entry, &lock->waiters);
+        rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
 }
 
 static void
@@ -300,20 +297,17 @@ 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_erase_cached(&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 **link = &task->pi_waiters.rb_root.rb_node;
         struct rb_node *parent = NULL;
         struct rt_mutex_waiter *entry;
-        int leftmost = 1;
+        bool leftmost = true;
 
         while (*link) {
                 parent = *link;
@@ -322,15 +316,12 @@ rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
                         link = &parent->rb_left;
                 } else {
                         link = &parent->rb_right;
-                        leftmost = 0;
+                        leftmost = false;
                 }
         }
 
-        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);
+        rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
 }
 
 static void
@@ -339,10 +330,7 @@ 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_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
         RB_CLEAR_NODE(&waiter->pi_tree_entry);
 }
 
@@ -1657,8 +1645,7 @@ void __rt_mutex_init(struct rt_mutex *lock, const char *name,
 {
         lock->owner = NULL;
         raw_spin_lock_init(&lock->wait_lock);
-        lock->waiters = RB_ROOT;
-        lock->waiters_leftmost = NULL;
+        lock->waiters = RB_ROOT_CACHED;
 
         if (name && key)
                 debug_rt_mutex_init(lock, name, key);
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 8d039b928d61..7453be0485a5 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -45,7 +45,7 @@ struct rt_mutex_waiter {
 
 static inline int rt_mutex_has_waiters(struct rt_mutex *lock)
 {
-        return !RB_EMPTY_ROOT(&lock->waiters);
+        return !RB_EMPTY_ROOT(&lock->waiters.rb_root);
 }
 
 static inline struct rt_mutex_waiter *
@@ -53,8 +53,8 @@ rt_mutex_top_waiter(struct rt_mutex *lock)
 {
         struct rt_mutex_waiter *w;
 
-        w = rb_entry(lock->waiters_leftmost, struct rt_mutex_waiter,
-                     tree_entry);
+        w = rb_entry(lock->waiters.rb_leftmost,
+                     struct rt_mutex_waiter, tree_entry);
         BUG_ON(w->lock != lock);
 
         return w;
@@ -62,14 +62,14 @@ rt_mutex_top_waiter(struct rt_mutex *lock)
 
 static inline int task_has_pi_waiters(struct task_struct *p)
 {
-        return !RB_EMPTY_ROOT(&p->pi_waiters);
+        return !RB_EMPTY_ROOT(&p->pi_waiters.rb_root);
 }
 
 static inline struct rt_mutex_waiter *
 task_top_pi_waiter(struct task_struct *p)
 {
-        return rb_entry(p->pi_waiters_leftmost, struct rt_mutex_waiter,
-                        pi_tree_entry);
+        return rb_entry(p->pi_waiters.rb_leftmost,
+                        struct rt_mutex_waiter, pi_tree_entry);
 }
 
 #else