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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) 2021-08-17 16:31:54 +02:00 committed by Ingo Molnar
parent aaa77de10b
commit 2674bd181f
2 changed files with 370 additions and 371 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

372
kernel/locking/mutex.c
View File

@ -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:
*/

369
kernel/locking/ww_mutex.h Normal file
View File

@ -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;
}
}