locking/ww_mutex: Split out the W/W implementation logic into kernel/locking/ww_mutex.h (2674bd18) · Commits · git / linux-net

kernel/locking/mutex.c

+1 −371

Original line number	Diff line number	Diff line
		@@ -281,215 +281,7 @@ void __sched mutex_lock(struct mutex *lock)
		EXPORT_SYMBOL(mutex_lock);
		#endif

		/*
		* 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);
		}
		#include "ww_mutex.h"

		#ifdef CONFIG_MUTEX_SPIN_ON_OWNER

		@@ -744,20 +536,6 @@ void __sched mutex_unlock(struct mutex *lock)
		}
		EXPORT_SYMBOL(mutex_unlock);

		static void __ww_mutex_unlock(struct ww_mutex *lock)
		{
		/*
		* The unlocking fastpath is the 0->1 transition from 'locked'
		* into 'unlocked' state:
		*/
		if (lock->ctx) {
		MUTEX_WARN_ON(!lock->ctx->acquired);
		if (lock->ctx->acquired > 0)
		lock->ctx->acquired--;
		lock->ctx = NULL;
		}
		}

		/**
		* ww_mutex_unlock - release the w/w mutex
		* @lock: the mutex to be released
		@@ -776,154 +554,6 @@ void __sched ww_mutex_unlock(struct ww_mutex *lock)
		}
		EXPORT_SYMBOL(ww_mutex_unlock);


		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;
		}

		/*
		* Lock a mutex (possibly interruptible), slowpath:
		*/

kernel/locking/ww_mutex.h

0 → 100644

+369 −0

Original line number	Diff line number	Diff line
		/* 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;
		}
		}