LXR linux/kernel/locking/rtmutex

   1/* SPDX-License-Identifier: GPL-2.0 */
   2/*
   3 * RT Mutexes: blocking mutual exclusion locks with PI support
   4 *
   5 * started by Ingo Molnar and Thomas Gleixner:
   6 *
   7 *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   8 *  Copyright (C) 2006, Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   9 *
  10 * This file contains the private data structure and API definitions.
  11 */
  12
  13#ifndef __KERNEL_RTMUTEX_COMMON_H
  14#define __KERNEL_RTMUTEX_COMMON_H
  15
  16#include <linux/debug_locks.h>
  17#include <linux/rtmutex.h>
  18#include <linux/sched/wake_q.h>
  19
  20/*
  21 * This is the control structure for tasks blocked on a rt_mutex,
  22 * which is allocated on the kernel stack on of the blocked task.
  23 *
  24 * @tree_entry:         pi node to enqueue into the mutex waiters tree
  25 * @pi_tree_entry:      pi node to enqueue into the mutex owner waiters tree
  26 * @task:               task reference to the blocked task
  27 * @lock:               Pointer to the rt_mutex on which the waiter blocks
  28 * @wake_state:         Wakeup state to use (TASK_NORMAL or TASK_RTLOCK_WAIT)
  29 * @prio:               Priority of the waiter
  30 * @deadline:           Deadline of the waiter if applicable
  31 * @ww_ctx:             WW context pointer
  32 */
  33struct rt_mutex_waiter {
  34        struct rb_node          tree_entry;
  35        struct rb_node          pi_tree_entry;
  36        struct task_struct      *task;
  37        struct rt_mutex_base    *lock;
  38        unsigned int            wake_state;
  39        int                     prio;
  40        u64                     deadline;
  41        struct ww_acquire_ctx   *ww_ctx;
  42};
  43
  44/**
  45 * rt_wake_q_head - Wrapper around regular wake_q_head to support
  46 *                  "sleeping" spinlocks on RT
  47 * @head:               The regular wake_q_head for sleeping lock variants
  48 * @rtlock_task:        Task pointer for RT lock (spin/rwlock) wakeups
  49 */
  50struct rt_wake_q_head {
  51        struct wake_q_head      head;
  52        struct task_struct      *rtlock_task;
  53};
  54
  55#define DEFINE_RT_WAKE_Q(name)                                          \
  56        struct rt_wake_q_head name = {                                  \
  57                .head           = WAKE_Q_HEAD_INITIALIZER(name.head),   \
  58                .rtlock_task    = NULL,                                 \
  59        }
  60
  61/*
  62 * PI-futex support (proxy locking functions, etc.):
  63 */
  64extern void rt_mutex_init_proxy_locked(struct rt_mutex_base *lock,
  65                                       struct task_struct *proxy_owner);
  66extern void rt_mutex_proxy_unlock(struct rt_mutex_base *lock);
  67extern int __rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
  68                                     struct rt_mutex_waiter *waiter,
  69                                     struct task_struct *task);
  70extern int rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
  71                                     struct rt_mutex_waiter *waiter,
  72                                     struct task_struct *task);
  73extern int rt_mutex_wait_proxy_lock(struct rt_mutex_base *lock,
  74                               struct hrtimer_sleeper *to,
  75                               struct rt_mutex_waiter *waiter);
  76extern bool rt_mutex_cleanup_proxy_lock(struct rt_mutex_base *lock,
  77                                 struct rt_mutex_waiter *waiter);
  78
  79extern int rt_mutex_futex_trylock(struct rt_mutex_base *l);
  80extern int __rt_mutex_futex_trylock(struct rt_mutex_base *l);
  81
  82extern void rt_mutex_futex_unlock(struct rt_mutex_base *lock);
  83extern bool __rt_mutex_futex_unlock(struct rt_mutex_base *lock,
  84                                struct rt_wake_q_head *wqh);
  85
  86extern void rt_mutex_postunlock(struct rt_wake_q_head *wqh);
  87
  88/*
  89 * Must be guarded because this header is included from rcu/tree_plugin.h
  90 * unconditionally.
  91 */
  92#ifdef CONFIG_RT_MUTEXES
  93static inline int rt_mutex_has_waiters(struct rt_mutex_base *lock)
  94{
  95        return !RB_EMPTY_ROOT(&lock->waiters.rb_root);
  96}
  97
  98/*
  99 * Lockless speculative check whether @waiter is still the top waiter on
 100 * @lock. This is solely comparing pointers and not derefencing the
 101 * leftmost entry which might be about to vanish.
 102 */
 103static inline bool rt_mutex_waiter_is_top_waiter(struct rt_mutex_base *lock,
 104                                                 struct rt_mutex_waiter *waiter)
 105{
 106        struct rb_node *leftmost = rb_first_cached(&lock->waiters);
 107
 108        return rb_entry(leftmost, struct rt_mutex_waiter, tree_entry) == waiter;
 109}
 110
 111static inline struct rt_mutex_waiter *rt_mutex_top_waiter(struct rt_mutex_base *lock)
 112{
 113        struct rb_node *leftmost = rb_first_cached(&lock->waiters);
 114        struct rt_mutex_waiter *w = NULL;
 115
 116        if (leftmost) {
 117                w = rb_entry(leftmost, struct rt_mutex_waiter, tree_entry);
 118                BUG_ON(w->lock != lock);
 119        }
 120        return w;
 121}
 122
 123static inline int task_has_pi_waiters(struct task_struct *p)
 124{
 125        return !RB_EMPTY_ROOT(&p->pi_waiters.rb_root);
 126}
 127
 128static inline struct rt_mutex_waiter *task_top_pi_waiter(struct task_struct *p)
 129{
 130        return rb_entry(p->pi_waiters.rb_leftmost, struct rt_mutex_waiter,
 131                        pi_tree_entry);
 132}
 133
 134#define RT_MUTEX_HAS_WAITERS    1UL
 135
 136static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
 137{
 138        unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
 139
 140        return (struct task_struct *) (owner & ~RT_MUTEX_HAS_WAITERS);
 141}
 142
 143/*
 144 * Constants for rt mutex functions which have a selectable deadlock
 145 * detection.
 146 *
 147 * RT_MUTEX_MIN_CHAINWALK:      Stops the lock chain walk when there are
 148 *                              no further PI adjustments to be made.
 149 *
 150 * RT_MUTEX_FULL_CHAINWALK:     Invoke deadlock detection with a full
 151 *                              walk of the lock chain.
 152 */
 153enum rtmutex_chainwalk {
 154        RT_MUTEX_MIN_CHAINWALK,
 155        RT_MUTEX_FULL_CHAINWALK,
 156};
 157
 158static inline void __rt_mutex_base_init(struct rt_mutex_base *lock)
 159{
 160        raw_spin_lock_init(&lock->wait_lock);
 161        lock->waiters = RB_ROOT_CACHED;
 162        lock->owner = NULL;
 163}
 164
 165/* Debug functions */
 166static inline void debug_rt_mutex_unlock(struct rt_mutex_base *lock)
 167{
 168        if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
 169                DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current);
 170}
 171
 172static inline void debug_rt_mutex_proxy_unlock(struct rt_mutex_base *lock)
 173{
 174        if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
 175                DEBUG_LOCKS_WARN_ON(!rt_mutex_owner(lock));
 176}
 177
 178static inline void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
 179{
 180        if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
 181                memset(waiter, 0x11, sizeof(*waiter));
 182}
 183
 184static inline void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
 185{
 186        if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
 187                memset(waiter, 0x22, sizeof(*waiter));
 188}
 189
 190static inline void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
 191{
 192        debug_rt_mutex_init_waiter(waiter);
 193        RB_CLEAR_NODE(&waiter->pi_tree_entry);
 194        RB_CLEAR_NODE(&waiter->tree_entry);
 195        waiter->wake_state = TASK_NORMAL;
 196        waiter->task = NULL;
 197}
 198
 199static inline void rt_mutex_init_rtlock_waiter(struct rt_mutex_waiter *waiter)
 200{
 201        rt_mutex_init_waiter(waiter);
 202        waiter->wake_state = TASK_RTLOCK_WAIT;
 203}
 204
 205#else /* CONFIG_RT_MUTEXES */
 206/* Used in rcu/tree_plugin.h */
 207static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
 208{
 209        return NULL;
 210}
 211#endif  /* !CONFIG_RT_MUTEXES */
 212
 213#endif
 214