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

#ifndef WW_RT

#define MUTEX           mutex
#define MUTEX_WAITER    mutex_waiter

static inline struct mutex_waiter *
__ww_waiter_first(struct mutex *lock)
{
        struct mutex_waiter *w;

        w = list_first_entry(&lock->wait_list, struct mutex_waiter, list);
        if (list_entry_is_head(w, &lock->wait_list, list))
                return NULL;

        return w;
}

static inline struct mutex_waiter *
__ww_waiter_next(struct mutex *lock, struct mutex_waiter *w)
{
        w = list_next_entry(w, list);
        if (list_entry_is_head(w, &lock->wait_list, list))
                return NULL;

        return w;
}

static inline struct mutex_waiter *
__ww_waiter_prev(struct mutex *lock, struct mutex_waiter *w)
{
        w = list_prev_entry(w, list);
        if (list_entry_is_head(w, &lock->wait_list, list))
                return NULL;

        return w;
}

static inline struct mutex_waiter *
__ww_waiter_last(struct mutex *lock)
{
        struct mutex_waiter *w;

        w = list_last_entry(&lock->wait_list, struct mutex_waiter, list);
        if (list_entry_is_head(w, &lock->wait_list, list))
                return NULL;

        return w;
}

static inline void
__ww_waiter_add(struct mutex *lock, struct mutex_waiter *waiter, struct mutex_waiter *pos)
{
        struct list_head *p = &lock->wait_list;
        if (pos)
                p = &pos->list;
        __mutex_add_waiter(lock, waiter, p);
}

static inline struct task_struct *
__ww_mutex_owner(struct mutex *lock)
{
        return __mutex_owner(lock);
}

static inline bool
__ww_mutex_has_waiters(struct mutex *lock)
{
        return atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS;
}

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

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

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

#else /* WW_RT */

#define MUTEX           rt_mutex
#define MUTEX_WAITER    rt_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)
{
#ifdef DEBUG_WW_MUTEXES
        /*
         * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
         * but released with a normal mutex_unlock in this call.
         *
         * This should never happen, always use ww_mutex_unlock.
         */
        DEBUG_LOCKS_WARN_ON(ww->ctx);

        /*
         * Not quite done after calling ww_acquire_done() ?
         */
        DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);

        if (ww_ctx->contending_lock) {
                /*
                 * After -EDEADLK you tried to
                 * acquire a different ww_mutex? Bad!
                 */
                DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);

                /*
                 * You called ww_mutex_lock after receiving -EDEADLK,
                 * but 'forgot' to unlock everything else first?
                 */
                DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
                ww_ctx->contending_lock = NULL;
        }

        /*
         * Naughty, using a different class will lead to undefined behavior!
         */
        DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
#endif
        ww_ctx->acquired++;
        ww->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)
{
/*
 * Can only do the RT prio for WW_RT, because task->prio isn't stable due to PI,
 * so the wait_list ordering will go wobbly. rt_mutex re-queues the waiter and
 * isn't affected by this.
 */
#ifdef WW_RT
        /* kernel prio; less is more */
        int a_prio = a->task->prio;
        int b_prio = b->task->prio;

        if (rt_prio(a_prio) || rt_prio(b_prio)) {

                if (a_prio > b_prio)
                        return true;

                if (a_prio < b_prio)
                        return false;

                /* equal static prio */

                if (dl_prio(a_prio)) {
                        if (dl_time_before(b->task->dl.deadline,
                                           a->task->dl.deadline))
                                return true;

                        if (dl_time_before(a->task->dl.deadline,
                                           b->task->dl.deadline))
                                return false;
                }

                /* equal prio */
        }
#endif

        /* FIFO order tie break -- bigger is younger */
        return (signed long)(a->stamp - b->stamp) > 0;
}

/*
 * 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)
{
        if (!ww_ctx->is_wait_die)
                return false;

        if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) {
#ifndef WW_RT
                debug_mutex_wake_waiter(lock, waiter);
#endif
                wake_up_process(waiter->task);
        }

        return true;
}

/*
 * 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)
{
        struct task_struct *owner = __ww_mutex_owner(lock);

        lockdep_assert_wait_lock_held(lock);

        /*
         * Possible through __ww_mutex_add_waiter() when we race with
         * ww_mutex_set_context_fastpath(). In that case we'll get here again
         * through __ww_mutex_check_waiters().
         */
        if (!hold_ctx)
                return false;

        /*
         * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
         * it cannot go away because we'll have FLAG_WAITERS set and hold
         * wait_lock.
         */
        if (!owner)
                return false;

        if (ww_ctx->acquired > 0 && __ww_ctx_less(hold_ctx, ww_ctx)) {
                hold_ctx->wounded = 1;

                /*
                 * wake_up_process() paired with set_current_state()
                 * inserts sufficient barriers to make sure @owner either sees
                 * it's wounded in __ww_mutex_check_kill() or has a
                 * wakeup pending to re-read the wounded state.
                 */
                if (owner != current)
                        wake_up_process(owner);

                return true;
        }

        return false;
}

/*
 * 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)
{
        struct MUTEX_WAITER *cur;

        lockdep_assert_wait_lock_held(lock);

        for (cur = __ww_waiter_first(lock); cur;
             cur = __ww_waiter_next(lock, cur)) {

                if (!cur->ww_ctx)
                        continue;

                if (__ww_mutex_die(lock, cur, ww_ctx) ||
                    __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
                        break;
        }
}

/*
 * 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)
{
        ww_mutex_lock_acquired(lock, ctx);

        /*
         * The lock->ctx update should be visible on all cores before
         * the WAITERS check is done, otherwise contended waiters might be
         * missed. The contended waiters will either see ww_ctx == NULL
         * and keep spinning, or it will acquire wait_lock, add itself
         * to waiter list and sleep.
         */
        smp_mb(); /* See comments above and below. */

        /*
         * [W] ww->ctx = ctx        [W] MUTEX_FLAG_WAITERS
         *     MB                       MB
         * [R] MUTEX_FLAG_WAITERS   [R] ww->ctx
         *
         * The memory barrier above pairs with the memory barrier in
         * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
         * and/or !empty list.
         */
        if (likely(!__ww_mutex_has_waiters(&lock->base)))
                return;

        /*
         * Uh oh, we raced in fastpath, check if any of the waiters need to
         * die or wound us.
         */
        lock_wait_lock(&lock->base);
        __ww_mutex_check_waiters(&lock->base, ctx);
        unlock_wait_lock(&lock->base);
}

static __always_inline int
__ww_mutex_kill(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
{
        if (ww_ctx->acquired > 0) {
#ifdef DEBUG_WW_MUTEXES
                struct ww_mutex *ww;

                ww = container_of(lock, struct ww_mutex, base);
                DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
                ww_ctx->contending_lock = ww;
#endif
                return -EDEADLK;
        }

        return 0;
}

/*
 * 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)
{
        struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
        struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
        struct MUTEX_WAITER *cur;

        if (ctx->acquired == 0)
                return 0;

        if (!ctx->is_wait_die) {
                if (ctx->wounded)
                        return __ww_mutex_kill(lock, ctx);

                return 0;
        }

        if (hold_ctx && __ww_ctx_less(ctx, hold_ctx))
                return __ww_mutex_kill(lock, ctx);

        /*
         * If there is a waiter in front of us that has a context, then its
         * stamp is earlier than ours and we must kill ourself.
         */
        for (cur = __ww_waiter_prev(lock, waiter); cur;
             cur = __ww_waiter_prev(lock, cur)) {

                if (!cur->ww_ctx)
                        continue;

                return __ww_mutex_kill(lock, ctx);
        }

        return 0;
}

/*
 * 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)
{
        struct MUTEX_WAITER *cur, *pos = NULL;
        bool is_wait_die;

        if (!ww_ctx) {
                __ww_waiter_add(lock, waiter, NULL);
                return 0;
        }

        is_wait_die = ww_ctx->is_wait_die;

        /*
         * Add the waiter before the first waiter with a higher stamp.
         * Waiters without a context are skipped to avoid starving
         * them. Wait-Die waiters may die here. Wound-Wait waiters
         * never die here, but they are sorted in stamp order and
         * may wound the lock holder.
         */
        for (cur = __ww_waiter_last(lock); cur;
             cur = __ww_waiter_prev(lock, cur)) {

                if (!cur->ww_ctx)
                        continue;

                if (__ww_ctx_less(ww_ctx, cur->ww_ctx)) {
                        /*
                         * Wait-Die: if we find an older context waiting, there
                         * is no point in queueing behind it, as we'd have to
                         * die the moment it would acquire the lock.
                         */
                        if (is_wait_die) {
                                int ret = __ww_mutex_kill(lock, ww_ctx);

                                if (ret)
                                        return ret;
                        }

                        break;
                }

                pos = cur;

                /* Wait-Die: ensure younger waiters die. */
                __ww_mutex_die(lock, cur, ww_ctx);
        }

        __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;
        }
}