locking/ww_mutex: Split out the W/W implementation logic into kernel/locking/ww_mutex.h
Split the W/W mutex helper functions out into a separate header file, so they can be shared with a rtmutex based variant later. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210815211304.396893399@linutronix.de
This commit is contained in:
Peter Zijlstra (Intel)
Ingo Molnar
Родитель
aaa77de10b
Коммит
2674bd181f
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@ -281,215 +281,7 @@ void __sched mutex_lock(struct mutex *lock)
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EXPORT_SYMBOL(mutex_lock);
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EXPORT_SYMBOL(mutex_lock);
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#endif
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#endif
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/*
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#include "ww_mutex.h"
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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 CONFIG_DEBUG_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 context @a is 'after' context @b. IOW, @a is a younger
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* transaction than @b and depending on algorithm either needs to wait for
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* @b or die.
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*/
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static inline bool __sched
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__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
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{
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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 younger 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 __sched
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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 &&
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__ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
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debug_mutex_wake_waiter(lock, waiter);
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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 younger @hold_ctx if it holds the lock.
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*
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* Wound the lock holder if there are waiters with older transactions than
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* 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 = __mutex_owner(lock);
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lockdep_assert_held(&lock->wait_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_stamp_after(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 later contexts waiting
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* 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 __sched
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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_held(&lock->wait_lock);
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list_for_each_entry(cur, &lock->wait_list, list) {
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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(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
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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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raw_spin_lock(&lock->base.wait_lock);
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__ww_mutex_check_waiters(&lock->base, ctx);
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raw_spin_unlock(&lock->base.wait_lock);
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}
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#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
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#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
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@ -744,20 +536,6 @@ void __sched mutex_unlock(struct mutex *lock)
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}
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}
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EXPORT_SYMBOL(mutex_unlock);
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EXPORT_SYMBOL(mutex_unlock);
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static void __ww_mutex_unlock(struct ww_mutex *lock)
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{
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/*
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* The unlocking fastpath is the 0->1 transition from 'locked'
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* into 'unlocked' state:
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*/
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if (lock->ctx) {
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MUTEX_WARN_ON(!lock->ctx->acquired);
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if (lock->ctx->acquired > 0)
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lock->ctx->acquired--;
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lock->ctx = NULL;
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}
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}
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/**
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/**
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* ww_mutex_unlock - release the w/w mutex
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* ww_mutex_unlock - release the w/w mutex
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* @lock: the mutex to be released
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* @lock: the mutex to be released
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@ -776,154 +554,6 @@ void __sched ww_mutex_unlock(struct ww_mutex *lock)
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}
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}
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EXPORT_SYMBOL(ww_mutex_unlock);
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EXPORT_SYMBOL(ww_mutex_unlock);
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static __always_inline int __sched
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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 CONFIG_DEBUG_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 __sched
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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_stamp_after(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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cur = waiter;
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list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
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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 __sched
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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;
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struct list_head *pos;
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bool is_wait_die;
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if (!ww_ctx) {
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__mutex_add_waiter(lock, waiter, &lock->wait_list);
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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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pos = &lock->wait_list;
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list_for_each_entry_reverse(cur, &lock->wait_list, list) {
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if (!cur->ww_ctx)
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continue;
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if (__ww_ctx_stamp_after(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->list;
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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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}
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__mutex_add_waiter(lock, waiter, pos);
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/*
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* Wound-Wait: if we're blocking on a mutex owned by a younger context,
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* wound that such that we might proceed.
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*/
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if (!is_wait_die) {
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struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
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/*
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* See ww_mutex_set_context_fastpath(). Orders setting
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* MUTEX_FLAG_WAITERS vs the ww->ctx load,
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* such that either we or the fastpath will wound @ww->ctx.
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||||||
*/
|
|
||||||
smp_mb();
|
|
||||||
__ww_mutex_wound(lock, ww_ctx, ww->ctx);
|
|
||||||
}
|
|
||||||
|
|
||||||
return 0;
|
|
||||||
}
|
|
||||||
|
|
||||||
/*
|
/*
|
||||||
* Lock a mutex (possibly interruptible), slowpath:
|
* Lock a mutex (possibly interruptible), slowpath:
|
||||||
*/
|
*/
|
||||||
|
|
|
||||||
|
|
@ -0,0 +1,369 @@
|
||||||
|
/* SPDX-License-Identifier: GPL-2.0-only */
|
||||||
|
|
||||||
|
/*
|
||||||
|
* 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 CONFIG_DEBUG_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 context @a is 'after' context @b. IOW, @a is a younger
|
||||||
|
* transaction than @b and depending on algorithm either needs to wait for
|
||||||
|
* @b or die.
|
||||||
|
*/
|
||||||
|
static inline bool __sched
|
||||||
|
__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
|
||||||
|
{
|
||||||
|
|
||||||
|
return (signed long)(a->stamp - b->stamp) > 0;
|
||||||
|
}
|
||||||
|
|
||||||
|
/*
|
||||||
|
* Wait-Die; wake a younger 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 __sched
|
||||||
|
__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_stamp_after(waiter->ww_ctx, ww_ctx)) {
|
||||||
|
debug_mutex_wake_waiter(lock, waiter);
|
||||||
|
wake_up_process(waiter->task);
|
||||||
|
}
|
||||||
|
|
||||||
|
return true;
|
||||||
|
}
|
||||||
|
|
||||||
|
/*
|
||||||
|
* Wound-Wait; wound a younger @hold_ctx if it holds the lock.
|
||||||
|
*
|
||||||
|
* Wound the lock holder if there are waiters with older 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 = __mutex_owner(lock);
|
||||||
|
|
||||||
|
lockdep_assert_held(&lock->wait_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_stamp_after(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 later 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 __sched
|
||||||
|
__ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
|
||||||
|
{
|
||||||
|
struct mutex_waiter *cur;
|
||||||
|
|
||||||
|
lockdep_assert_held(&lock->wait_lock);
|
||||||
|
|
||||||
|
list_for_each_entry(cur, &lock->wait_list, list) {
|
||||||
|
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(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
|
||||||
|
return;
|
||||||
|
|
||||||
|
/*
|
||||||
|
* Uh oh, we raced in fastpath, check if any of the waiters need to
|
||||||
|
* die or wound us.
|
||||||
|
*/
|
||||||
|
raw_spin_lock(&lock->base.wait_lock);
|
||||||
|
__ww_mutex_check_waiters(&lock->base, ctx);
|
||||||
|
raw_spin_unlock(&lock->base.wait_lock);
|
||||||
|
}
|
||||||
|
|
||||||
|
static __always_inline int __sched
|
||||||
|
__ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
|
||||||
|
{
|
||||||
|
if (ww_ctx->acquired > 0) {
|
||||||
|
#ifdef CONFIG_DEBUG_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 __sched
|
||||||
|
__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_stamp_after(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.
|
||||||
|
*/
|
||||||
|
cur = waiter;
|
||||||
|
list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
|
||||||
|
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 __sched
|
||||||
|
__ww_mutex_add_waiter(struct mutex_waiter *waiter,
|
||||||
|
struct mutex *lock,
|
||||||
|
struct ww_acquire_ctx *ww_ctx)
|
||||||
|
{
|
||||||
|
struct mutex_waiter *cur;
|
||||||
|
struct list_head *pos;
|
||||||
|
bool is_wait_die;
|
||||||
|
|
||||||
|
if (!ww_ctx) {
|
||||||
|
__mutex_add_waiter(lock, waiter, &lock->wait_list);
|
||||||
|
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.
|
||||||
|
*/
|
||||||
|
pos = &lock->wait_list;
|
||||||
|
list_for_each_entry_reverse(cur, &lock->wait_list, list) {
|
||||||
|
if (!cur->ww_ctx)
|
||||||
|
continue;
|
||||||
|
|
||||||
|
if (__ww_ctx_stamp_after(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->list;
|
||||||
|
|
||||||
|
/* Wait-Die: ensure younger waiters die. */
|
||||||
|
__ww_mutex_die(lock, cur, ww_ctx);
|
||||||
|
}
|
||||||
|
|
||||||
|
__mutex_add_waiter(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 CONFIG_DEBUG_MUTEXES
|
||||||
|
DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
|
||||||
|
#endif
|
||||||
|
if (lock->ctx->acquired > 0)
|
||||||
|
lock->ctx->acquired--;
|
||||||
|
lock->ctx = NULL;
|
||||||
|
}
|
||||||
|
}
|
||||||
Загрузка…
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