ww_mutex.h | Explore in Territory

/* SPDX-License-Identifier: GPL-2.0-only */

#ifndef WW_RT

#define MUTEX …
#define MUTEX_WAITER …

static inline struct mutex_waiter *
__ww_waiter_first(struct mutex *lock)
{ … }

static inline struct mutex_waiter *
__ww_waiter_next(struct mutex *lock, struct mutex_waiter *w)
{ … }

static inline struct mutex_waiter *
__ww_waiter_prev(struct mutex *lock, struct mutex_waiter *w)
{ … }

static inline struct mutex_waiter *
__ww_waiter_last(struct mutex *lock)
{ … }

static inline void
__ww_waiter_add(struct mutex *lock, struct mutex_waiter *waiter, struct mutex_waiter *pos)
{ … }

static inline struct task_struct *
__ww_mutex_owner(struct mutex *lock)
{ … }

static inline bool
__ww_mutex_has_waiters(struct mutex *lock)
{ … }

static inline void lock_wait_lock(struct mutex *lock)
{ … }

static inline void unlock_wait_lock(struct mutex *lock)
{ … }

static inline void lockdep_assert_wait_lock_held(struct mutex *lock)
{ … }

#else /* WW_RT */

#define MUTEX …
#define MUTEX_WAITER …

static inline struct rt_mutex_waiter *
__ww_waiter_first(struct rt_mutex *lock)
{
	struct rb_node *n = rb_first(&lock->rtmutex.waiters.rb_root);
	if (!n)
		return NULL;
	return rb_entry(n, struct rt_mutex_waiter, tree.entry);
}

static inline struct rt_mutex_waiter *
__ww_waiter_next(struct rt_mutex *lock, struct rt_mutex_waiter *w)
{
	struct rb_node *n = rb_next(&w->tree.entry);
	if (!n)
		return NULL;
	return rb_entry(n, struct rt_mutex_waiter, tree.entry);
}

static inline struct rt_mutex_waiter *
__ww_waiter_prev(struct rt_mutex *lock, struct rt_mutex_waiter *w)
{
	struct rb_node *n = rb_prev(&w->tree.entry);
	if (!n)
		return NULL;
	return rb_entry(n, struct rt_mutex_waiter, tree.entry);
}

static inline struct rt_mutex_waiter *
__ww_waiter_last(struct rt_mutex *lock)
{
	struct rb_node *n = rb_last(&lock->rtmutex.waiters.rb_root);
	if (!n)
		return NULL;
	return rb_entry(n, struct rt_mutex_waiter, tree.entry);
}

static inline void
__ww_waiter_add(struct rt_mutex *lock, struct rt_mutex_waiter *waiter, struct rt_mutex_waiter *pos)
{
	/* RT unconditionally adds the waiter first and then removes it on error */
}

static inline struct task_struct *
__ww_mutex_owner(struct rt_mutex *lock)
{
	return rt_mutex_owner(&lock->rtmutex);
}

static inline bool
__ww_mutex_has_waiters(struct rt_mutex *lock)
{
	return rt_mutex_has_waiters(&lock->rtmutex);
}

static inline void lock_wait_lock(struct rt_mutex *lock)
{
	raw_spin_lock(&lock->rtmutex.wait_lock);
}

static inline void unlock_wait_lock(struct rt_mutex *lock)
{
	raw_spin_unlock(&lock->rtmutex.wait_lock);
}

static inline void lockdep_assert_wait_lock_held(struct rt_mutex *lock)
{
	lockdep_assert_held(&lock->rtmutex.wait_lock);
}

#endif /* WW_RT */

/*
 * Wait-Die:
 *   The newer transactions are killed when:
 *     It (the new transaction) makes a request for a lock being held
 *     by an older transaction.
 *
 * Wound-Wait:
 *   The newer transactions are wounded when:
 *     An older transaction makes a request for a lock being held by
 *     the newer transaction.
 */

/*
 * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
 * it.
 */
static __always_inline void
ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
{ … }

/*
 * Determine if @a is 'less' than @b. IOW, either @a is a lower priority task
 * or, when of equal priority, a younger transaction than @b.
 *
 * Depending on the algorithm, @a will either need to wait for @b, or die.
 */
static inline bool
__ww_ctx_less(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
{ … }

/*
 * Wait-Die; wake a lesser waiter context (when locks held) such that it can
 * die.
 *
 * Among waiters with context, only the first one can have other locks acquired
 * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
 * __ww_mutex_check_kill() wake any but the earliest context.
 */
static bool
__ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
	       struct ww_acquire_ctx *ww_ctx)
{ … }

/*
 * Wound-Wait; wound a lesser @hold_ctx if it holds the lock.
 *
 * Wound the lock holder if there are waiters with more important transactions
 * than the lock holders. Even if multiple waiters may wound the lock holder,
 * it's sufficient that only one does.
 */
static bool __ww_mutex_wound(struct MUTEX *lock,
			     struct ww_acquire_ctx *ww_ctx,
			     struct ww_acquire_ctx *hold_ctx)
{ … }

/*
 * We just acquired @lock under @ww_ctx, if there are more important contexts
 * waiting behind us on the wait-list, check if they need to die, or wound us.
 *
 * See __ww_mutex_add_waiter() for the list-order construction; basically the
 * list is ordered by stamp, smallest (oldest) first.
 *
 * This relies on never mixing wait-die/wound-wait on the same wait-list;
 * which is currently ensured by that being a ww_class property.
 *
 * The current task must not be on the wait list.
 */
static void
__ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
{ … }

/*
 * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
 * and wake up any waiters so they can recheck.
 */
static __always_inline void
ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{ … }

static __always_inline int
__ww_mutex_kill(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
{ … }

/*
 * Check the wound condition for the current lock acquire.
 *
 * Wound-Wait: If we're wounded, kill ourself.
 *
 * Wait-Die: If we're trying to acquire a lock already held by an older
 *           context, kill ourselves.
 *
 * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
 * look at waiters before us in the wait-list.
 */
static inline int
__ww_mutex_check_kill(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
		      struct ww_acquire_ctx *ctx)
{ … }

/*
 * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
 * first. Such that older contexts are preferred to acquire the lock over
 * younger contexts.
 *
 * Waiters without context are interspersed in FIFO order.
 *
 * Furthermore, for Wait-Die kill ourself immediately when possible (there are
 * older contexts already waiting) to avoid unnecessary waiting and for
 * Wound-Wait ensure we wound the owning context when it is younger.
 */
static inline int
__ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
		      struct MUTEX *lock,
		      struct ww_acquire_ctx *ww_ctx)
{ … }

static inline void __ww_mutex_unlock(struct ww_mutex *lock)
{ … }
linux/kernel/locking/ww_mutex.h
