kernel/locking/mutex.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Mutexes: blocking mutual exclusion locks
   4  *
   5  * started by Ingo Molnar:
   6  *
   7  *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   8  */
   9
  10 /*
  11  * This is the control structure for tasks blocked on mutex, which resides
  12  * on the blocked task's kernel stack:
  13  */
  14 struct mutex_waiter {
  15         struct list_head        list;
  16         struct task_struct      *task;
  17         struct ww_acquire_ctx   *ww_ctx;
  18 #ifdef CONFIG_DEBUG_MUTEXES
  19         void                    *magic;
  20 #endif
  21 };
  22
  23 /*
  24  * @owner: contains: 'struct task_struct *' to the current lock owner,
  25  * NULL means not owned. Since task_struct pointers are aligned at
  26  * at least L1_CACHE_BYTES, we have low bits to store extra state.
  27  *
  28  * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
  29  * Bit1 indicates unlock needs to hand the lock to the top-waiter
  30  * Bit2 indicates handoff has been done and we're waiting for pickup.
  31  */
  32 #define MUTEX_FLAG_WAITERS      0x01
  33 #define MUTEX_FLAG_HANDOFF      0x02
  34 #define MUTEX_FLAG_PICKUP       0x04
  35
  36 #define MUTEX_FLAGS             0x07
  37
  38 /*
  39  * Internal helper function; C doesn't allow us to hide it :/
  40  *
  41  * DO NOT USE (outside of mutex & scheduler code).
  42  */
  43 static inline struct task_struct *__mutex_owner(struct mutex *lock)
  44 {
  45         if (!lock)
  46                 return NULL;
  47         return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
  48 }
  49
  50 #ifdef CONFIG_DEBUG_MUTEXES
  51 extern void debug_mutex_lock_common(struct mutex *lock,
  52                                     struct mutex_waiter *waiter);
  53 extern void debug_mutex_wake_waiter(struct mutex *lock,
  54                                     struct mutex_waiter *waiter);
  55 extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
  56 extern void debug_mutex_add_waiter(struct mutex *lock,
  57                                    struct mutex_waiter *waiter,
  58                                    struct task_struct *task);
  59 extern void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
  60                                       struct task_struct *task);
  61 extern void debug_mutex_unlock(struct mutex *lock);
  62 extern void debug_mutex_init(struct mutex *lock, const char *name,
  63                              struct lock_class_key *key);
  64 #else /* CONFIG_DEBUG_MUTEXES */
  65 # define debug_mutex_lock_common(lock, waiter)          do { } while (0)
  66 # define debug_mutex_wake_waiter(lock, waiter)          do { } while (0)
  67 # define debug_mutex_free_waiter(waiter)                do { } while (0)
  68 # define debug_mutex_add_waiter(lock, waiter, ti)       do { } while (0)
  69 # define debug_mutex_remove_waiter(lock, waiter, ti)    do { } while (0)
  70 # define debug_mutex_unlock(lock)                       do { } while (0)
  71 # define debug_mutex_init(lock, name, key)              do { } while (0)
  72 #endif /* !CONFIG_DEBUG_MUTEXES */