570 lines
14 KiB
C
570 lines
14 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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#ifndef WW_RT
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#define MUTEX mutex
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#define MUTEX_WAITER mutex_waiter
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static inline struct mutex_waiter *
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__ww_waiter_first(struct mutex *lock)
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{
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struct mutex_waiter *w;
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w = list_first_entry(&lock->wait_list, struct mutex_waiter, list);
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if (list_entry_is_head(w, &lock->wait_list, list))
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return NULL;
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return w;
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}
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static inline struct mutex_waiter *
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__ww_waiter_next(struct mutex *lock, struct mutex_waiter *w)
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{
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w = list_next_entry(w, list);
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if (list_entry_is_head(w, &lock->wait_list, list))
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return NULL;
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return w;
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}
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static inline struct mutex_waiter *
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__ww_waiter_prev(struct mutex *lock, struct mutex_waiter *w)
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{
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w = list_prev_entry(w, list);
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if (list_entry_is_head(w, &lock->wait_list, list))
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return NULL;
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return w;
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}
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static inline struct mutex_waiter *
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__ww_waiter_last(struct mutex *lock)
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{
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struct mutex_waiter *w;
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w = list_last_entry(&lock->wait_list, struct mutex_waiter, list);
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if (list_entry_is_head(w, &lock->wait_list, list))
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return NULL;
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return w;
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}
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static inline void
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__ww_waiter_add(struct mutex *lock, struct mutex_waiter *waiter, struct mutex_waiter *pos)
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{
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struct list_head *p = &lock->wait_list;
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if (pos)
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p = &pos->list;
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__mutex_add_waiter(lock, waiter, p);
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}
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static inline struct task_struct *
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__ww_mutex_owner(struct mutex *lock)
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{
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return __mutex_owner(lock);
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}
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static inline bool
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__ww_mutex_has_waiters(struct mutex *lock)
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{
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return atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS;
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}
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static inline void lock_wait_lock(struct mutex *lock)
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{
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raw_spin_lock(&lock->wait_lock);
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}
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static inline void unlock_wait_lock(struct mutex *lock)
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{
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raw_spin_unlock(&lock->wait_lock);
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}
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static inline void lockdep_assert_wait_lock_held(struct mutex *lock)
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{
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lockdep_assert_held(&lock->wait_lock);
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}
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#else /* WW_RT */
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#define MUTEX rt_mutex
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#define MUTEX_WAITER rt_mutex_waiter
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static inline struct rt_mutex_waiter *
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__ww_waiter_first(struct rt_mutex *lock)
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{
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struct rb_node *n = rb_first(&lock->rtmutex.waiters.rb_root);
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if (!n)
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return NULL;
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return rb_entry(n, struct rt_mutex_waiter, tree_entry);
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}
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static inline struct rt_mutex_waiter *
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__ww_waiter_next(struct rt_mutex *lock, struct rt_mutex_waiter *w)
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{
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struct rb_node *n = rb_next(&w->tree_entry);
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if (!n)
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return NULL;
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return rb_entry(n, struct rt_mutex_waiter, tree_entry);
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}
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static inline struct rt_mutex_waiter *
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__ww_waiter_prev(struct rt_mutex *lock, struct rt_mutex_waiter *w)
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{
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struct rb_node *n = rb_prev(&w->tree_entry);
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if (!n)
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return NULL;
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return rb_entry(n, struct rt_mutex_waiter, tree_entry);
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}
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static inline struct rt_mutex_waiter *
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__ww_waiter_last(struct rt_mutex *lock)
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{
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struct rb_node *n = rb_last(&lock->rtmutex.waiters.rb_root);
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if (!n)
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return NULL;
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return rb_entry(n, struct rt_mutex_waiter, tree_entry);
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}
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static inline void
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__ww_waiter_add(struct rt_mutex *lock, struct rt_mutex_waiter *waiter, struct rt_mutex_waiter *pos)
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{
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/* RT unconditionally adds the waiter first and then removes it on error */
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}
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static inline struct task_struct *
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__ww_mutex_owner(struct rt_mutex *lock)
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{
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return rt_mutex_owner(&lock->rtmutex);
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}
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static inline bool
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__ww_mutex_has_waiters(struct rt_mutex *lock)
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{
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return rt_mutex_has_waiters(&lock->rtmutex);
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}
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static inline void lock_wait_lock(struct rt_mutex *lock)
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{
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raw_spin_lock(&lock->rtmutex.wait_lock);
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}
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static inline void unlock_wait_lock(struct rt_mutex *lock)
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{
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raw_spin_unlock(&lock->rtmutex.wait_lock);
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}
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static inline void lockdep_assert_wait_lock_held(struct rt_mutex *lock)
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{
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lockdep_assert_held(&lock->rtmutex.wait_lock);
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}
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#endif /* WW_RT */
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/*
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* Wait-Die:
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* The newer transactions are killed when:
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* It (the new transaction) makes a request for a lock being held
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* by an older transaction.
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*
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* Wound-Wait:
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* The newer transactions are wounded when:
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* An older transaction makes a request for a lock being held by
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* the newer transaction.
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*/
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/*
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* Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
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* it.
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*/
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static __always_inline void
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ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
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{
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#ifdef DEBUG_WW_MUTEXES
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/*
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* If this WARN_ON triggers, you used ww_mutex_lock to acquire,
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* but released with a normal mutex_unlock in this call.
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*
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* This should never happen, always use ww_mutex_unlock.
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*/
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DEBUG_LOCKS_WARN_ON(ww->ctx);
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/*
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* Not quite done after calling ww_acquire_done() ?
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
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if (ww_ctx->contending_lock) {
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/*
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* After -EDEADLK you tried to
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* acquire a different ww_mutex? Bad!
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
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/*
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* You called ww_mutex_lock after receiving -EDEADLK,
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* but 'forgot' to unlock everything else first?
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
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ww_ctx->contending_lock = NULL;
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}
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/*
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* Naughty, using a different class will lead to undefined behavior!
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*/
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DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
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#endif
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ww_ctx->acquired++;
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ww->ctx = ww_ctx;
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}
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/*
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* Determine if @a is 'less' than @b. IOW, either @a is a lower priority task
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* or, when of equal priority, a younger transaction than @b.
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*
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* Depending on the algorithm, @a will either need to wait for @b, or die.
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*/
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static inline bool
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__ww_ctx_less(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
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{
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/*
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* Can only do the RT prio for WW_RT, because task->prio isn't stable due to PI,
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* so the wait_list ordering will go wobbly. rt_mutex re-queues the waiter and
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* isn't affected by this.
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*/
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#ifdef WW_RT
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/* kernel prio; less is more */
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int a_prio = a->task->prio;
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int b_prio = b->task->prio;
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if (rt_prio(a_prio) || rt_prio(b_prio)) {
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if (a_prio > b_prio)
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return true;
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if (a_prio < b_prio)
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return false;
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/* equal static prio */
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if (dl_prio(a_prio)) {
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if (dl_time_before(b->task->dl.deadline,
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a->task->dl.deadline))
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return true;
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if (dl_time_before(a->task->dl.deadline,
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b->task->dl.deadline))
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return false;
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}
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/* equal prio */
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}
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#endif
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/* FIFO order tie break -- bigger is younger */
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return (signed long)(a->stamp - b->stamp) > 0;
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}
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/*
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* Wait-Die; wake a lesser waiter context (when locks held) such that it can
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* die.
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*
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* Among waiters with context, only the first one can have other locks acquired
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* already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
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* __ww_mutex_check_kill() wake any but the earliest context.
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*/
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static bool
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__ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
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struct ww_acquire_ctx *ww_ctx)
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{
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if (!ww_ctx->is_wait_die)
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return false;
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if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) {
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#ifndef WW_RT
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debug_mutex_wake_waiter(lock, waiter);
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#endif
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wake_up_process(waiter->task);
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}
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return true;
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}
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/*
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* Wound-Wait; wound a lesser @hold_ctx if it holds the lock.
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*
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* Wound the lock holder if there are waiters with more important transactions
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* than the lock holders. Even if multiple waiters may wound the lock holder,
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* it's sufficient that only one does.
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*/
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static bool __ww_mutex_wound(struct MUTEX *lock,
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struct ww_acquire_ctx *ww_ctx,
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struct ww_acquire_ctx *hold_ctx)
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{
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struct task_struct *owner = __ww_mutex_owner(lock);
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lockdep_assert_wait_lock_held(lock);
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/*
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* Possible through __ww_mutex_add_waiter() when we race with
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* ww_mutex_set_context_fastpath(). In that case we'll get here again
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* through __ww_mutex_check_waiters().
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*/
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if (!hold_ctx)
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return false;
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/*
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* Can have !owner because of __mutex_unlock_slowpath(), but if owner,
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* it cannot go away because we'll have FLAG_WAITERS set and hold
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* wait_lock.
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*/
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if (!owner)
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return false;
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if (ww_ctx->acquired > 0 && __ww_ctx_less(hold_ctx, ww_ctx)) {
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hold_ctx->wounded = 1;
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/*
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* wake_up_process() paired with set_current_state()
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* inserts sufficient barriers to make sure @owner either sees
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* it's wounded in __ww_mutex_check_kill() or has a
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* wakeup pending to re-read the wounded state.
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*/
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if (owner != current)
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wake_up_process(owner);
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return true;
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}
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return false;
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}
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/*
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* We just acquired @lock under @ww_ctx, if there are more important contexts
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* waiting behind us on the wait-list, check if they need to die, or wound us.
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*
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* See __ww_mutex_add_waiter() for the list-order construction; basically the
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* list is ordered by stamp, smallest (oldest) first.
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*
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* This relies on never mixing wait-die/wound-wait on the same wait-list;
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* which is currently ensured by that being a ww_class property.
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*
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* The current task must not be on the wait list.
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*/
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static void
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__ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
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{
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struct MUTEX_WAITER *cur;
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lockdep_assert_wait_lock_held(lock);
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for (cur = __ww_waiter_first(lock); cur;
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cur = __ww_waiter_next(lock, cur)) {
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if (!cur->ww_ctx)
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continue;
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if (__ww_mutex_die(lock, cur, ww_ctx) ||
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__ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
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break;
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}
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}
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/*
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* After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
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* and wake up any waiters so they can recheck.
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*/
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static __always_inline void
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ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
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{
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ww_mutex_lock_acquired(lock, ctx);
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/*
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* The lock->ctx update should be visible on all cores before
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* the WAITERS check is done, otherwise contended waiters might be
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* missed. The contended waiters will either see ww_ctx == NULL
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* and keep spinning, or it will acquire wait_lock, add itself
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* to waiter list and sleep.
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*/
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smp_mb(); /* See comments above and below. */
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/*
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* [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
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* MB MB
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* [R] MUTEX_FLAG_WAITERS [R] ww->ctx
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*
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* The memory barrier above pairs with the memory barrier in
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* __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
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* and/or !empty list.
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*/
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if (likely(!__ww_mutex_has_waiters(&lock->base)))
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return;
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/*
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* Uh oh, we raced in fastpath, check if any of the waiters need to
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* die or wound us.
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*/
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lock_wait_lock(&lock->base);
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__ww_mutex_check_waiters(&lock->base, ctx);
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unlock_wait_lock(&lock->base);
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}
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static __always_inline int
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__ww_mutex_kill(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
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{
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if (ww_ctx->acquired > 0) {
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#ifdef DEBUG_WW_MUTEXES
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struct ww_mutex *ww;
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ww = container_of(lock, struct ww_mutex, base);
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DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
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ww_ctx->contending_lock = ww;
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#endif
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return -EDEADLK;
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}
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return 0;
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}
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/*
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* Check the wound condition for the current lock acquire.
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*
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* Wound-Wait: If we're wounded, kill ourself.
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*
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* Wait-Die: If we're trying to acquire a lock already held by an older
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* context, kill ourselves.
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*
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* Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
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* look at waiters before us in the wait-list.
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*/
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static inline int
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__ww_mutex_check_kill(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
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struct ww_acquire_ctx *ctx)
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{
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struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
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struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
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struct MUTEX_WAITER *cur;
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if (ctx->acquired == 0)
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return 0;
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if (!ctx->is_wait_die) {
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if (ctx->wounded)
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return __ww_mutex_kill(lock, ctx);
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return 0;
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}
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if (hold_ctx && __ww_ctx_less(ctx, hold_ctx))
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return __ww_mutex_kill(lock, ctx);
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/*
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* If there is a waiter in front of us that has a context, then its
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* stamp is earlier than ours and we must kill ourself.
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*/
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for (cur = __ww_waiter_prev(lock, waiter); cur;
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cur = __ww_waiter_prev(lock, cur)) {
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if (!cur->ww_ctx)
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continue;
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return __ww_mutex_kill(lock, ctx);
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}
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return 0;
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}
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/*
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* Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
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* first. Such that older contexts are preferred to acquire the lock over
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* younger contexts.
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*
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* Waiters without context are interspersed in FIFO order.
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*
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* Furthermore, for Wait-Die kill ourself immediately when possible (there are
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* older contexts already waiting) to avoid unnecessary waiting and for
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* Wound-Wait ensure we wound the owning context when it is younger.
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*/
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static inline int
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__ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
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struct MUTEX *lock,
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struct ww_acquire_ctx *ww_ctx)
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{
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struct MUTEX_WAITER *cur, *pos = NULL;
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bool is_wait_die;
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if (!ww_ctx) {
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__ww_waiter_add(lock, waiter, NULL);
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return 0;
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}
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is_wait_die = ww_ctx->is_wait_die;
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/*
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* Add the waiter before the first waiter with a higher stamp.
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* Waiters without a context are skipped to avoid starving
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* them. Wait-Die waiters may die here. Wound-Wait waiters
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* never die here, but they are sorted in stamp order and
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* may wound the lock holder.
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*/
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for (cur = __ww_waiter_last(lock); cur;
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cur = __ww_waiter_prev(lock, cur)) {
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if (!cur->ww_ctx)
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continue;
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if (__ww_ctx_less(ww_ctx, cur->ww_ctx)) {
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/*
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* Wait-Die: if we find an older context waiting, there
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* is no point in queueing behind it, as we'd have to
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* die the moment it would acquire the lock.
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*/
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if (is_wait_die) {
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int ret = __ww_mutex_kill(lock, ww_ctx);
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if (ret)
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return ret;
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}
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break;
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}
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pos = cur;
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/* Wait-Die: ensure younger waiters die. */
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__ww_mutex_die(lock, cur, ww_ctx);
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}
|
|
|
|
__ww_waiter_add(lock, waiter, pos);
|
|
|
|
/*
|
|
* Wound-Wait: if we're blocking on a mutex owned by a younger context,
|
|
* wound that such that we might proceed.
|
|
*/
|
|
if (!is_wait_die) {
|
|
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
|
|
|
|
/*
|
|
* See ww_mutex_set_context_fastpath(). Orders setting
|
|
* MUTEX_FLAG_WAITERS vs the ww->ctx load,
|
|
* such that either we or the fastpath will wound @ww->ctx.
|
|
*/
|
|
smp_mb();
|
|
__ww_mutex_wound(lock, ww_ctx, ww->ctx);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
static inline void __ww_mutex_unlock(struct ww_mutex *lock)
|
|
{
|
|
if (lock->ctx) {
|
|
#ifdef DEBUG_WW_MUTEXES
|
|
DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
|
|
#endif
|
|
if (lock->ctx->acquired > 0)
|
|
lock->ctx->acquired--;
|
|
lock->ctx = NULL;
|
|
}
|
|
}
|