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rt_mutex: add proxy lock routines
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This patch is a prerequisite for futex requeue_pi. It basically splits
rt_mutex_slowlock() right down the middle, just before the first call
to schedule(). It further adds helper functions which make use of the
split and provide the rt-mutex preliminaries for futex requeue_pi.

Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Darren Hart authored and Thomas Gleixner committed Apr 6, 2009
1 parent dd97399 commit 8dac456
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Showing 2 changed files with 195 additions and 53 deletions.
240 changes: 187 additions & 53 deletions kernel/rtmutex.c
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Original file line number Diff line number Diff line change
Expand Up @@ -300,7 +300,8 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
* assigned pending owner [which might not have taken the
* lock yet]:
*/
static inline int try_to_steal_lock(struct rt_mutex *lock)
static inline int try_to_steal_lock(struct rt_mutex *lock,
struct task_struct *task)
{
struct task_struct *pendowner = rt_mutex_owner(lock);
struct rt_mutex_waiter *next;
Expand All @@ -309,11 +310,11 @@ static inline int try_to_steal_lock(struct rt_mutex *lock)
if (!rt_mutex_owner_pending(lock))
return 0;

if (pendowner == current)
if (pendowner == task)
return 1;

spin_lock_irqsave(&pendowner->pi_lock, flags);
if (current->prio >= pendowner->prio) {
if (task->prio >= pendowner->prio) {
spin_unlock_irqrestore(&pendowner->pi_lock, flags);
return 0;
}
Expand All @@ -338,21 +339,21 @@ static inline int try_to_steal_lock(struct rt_mutex *lock)
* We are going to steal the lock and a waiter was
* enqueued on the pending owners pi_waiters queue. So
* we have to enqueue this waiter into
* current->pi_waiters list. This covers the case,
* where current is boosted because it holds another
* task->pi_waiters list. This covers the case,
* where task is boosted because it holds another
* lock and gets unboosted because the booster is
* interrupted, so we would delay a waiter with higher
* priority as current->normal_prio.
* priority as task->normal_prio.
*
* Note: in the rare case of a SCHED_OTHER task changing
* its priority and thus stealing the lock, next->task
* might be current:
* might be task:
*/
if (likely(next->task != current)) {
spin_lock_irqsave(&current->pi_lock, flags);
plist_add(&next->pi_list_entry, &current->pi_waiters);
__rt_mutex_adjust_prio(current);
spin_unlock_irqrestore(&current->pi_lock, flags);
if (likely(next->task != task)) {
spin_lock_irqsave(&task->pi_lock, flags);
plist_add(&next->pi_list_entry, &task->pi_waiters);
__rt_mutex_adjust_prio(task);
spin_unlock_irqrestore(&task->pi_lock, flags);
}
return 1;
}
Expand Down Expand Up @@ -389,7 +390,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock)
*/
mark_rt_mutex_waiters(lock);

if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
if (rt_mutex_owner(lock) && !try_to_steal_lock(lock, current))
return 0;

/* We got the lock. */
Expand All @@ -411,28 +412,29 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock)
*/
static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task,
int detect_deadlock)
{
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex_waiter *top_waiter = waiter;
unsigned long flags;
int chain_walk = 0, res;

spin_lock_irqsave(&current->pi_lock, flags);
__rt_mutex_adjust_prio(current);
waiter->task = current;
spin_lock_irqsave(&task->pi_lock, flags);
__rt_mutex_adjust_prio(task);
waiter->task = task;
waiter->lock = lock;
plist_node_init(&waiter->list_entry, current->prio);
plist_node_init(&waiter->pi_list_entry, current->prio);
plist_node_init(&waiter->list_entry, task->prio);
plist_node_init(&waiter->pi_list_entry, task->prio);

/* Get the top priority waiter on the lock */
if (rt_mutex_has_waiters(lock))
top_waiter = rt_mutex_top_waiter(lock);
plist_add(&waiter->list_entry, &lock->wait_list);

current->pi_blocked_on = waiter;
task->pi_blocked_on = waiter;

spin_unlock_irqrestore(&current->pi_lock, flags);
spin_unlock_irqrestore(&task->pi_lock, flags);

if (waiter == rt_mutex_top_waiter(lock)) {
spin_lock_irqsave(&owner->pi_lock, flags);
Expand Down Expand Up @@ -460,7 +462,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
spin_unlock(&lock->wait_lock);

res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
current);
task);

spin_lock(&lock->wait_lock);

Expand Down Expand Up @@ -605,37 +607,25 @@ void rt_mutex_adjust_pi(struct task_struct *task)
rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
}

/*
* Slow path lock function:
/**
* __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
* @lock: the rt_mutex to take
* @state: the state the task should block in (TASK_INTERRUPTIBLE
* or TASK_UNINTERRUPTIBLE)
* @timeout: the pre-initialized and started timer, or NULL for none
* @waiter: the pre-initialized rt_mutex_waiter
* @detect_deadlock: passed to task_blocks_on_rt_mutex
*
* lock->wait_lock must be held by the caller.
*/
static int __sched
rt_mutex_slowlock(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
int detect_deadlock)
__rt_mutex_slowlock(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
struct rt_mutex_waiter *waiter,
int detect_deadlock)
{
struct rt_mutex_waiter waiter;
int ret = 0;

debug_rt_mutex_init_waiter(&waiter);
waiter.task = NULL;

spin_lock(&lock->wait_lock);

/* Try to acquire the lock again: */
if (try_to_take_rt_mutex(lock)) {
spin_unlock(&lock->wait_lock);
return 0;
}

set_current_state(state);

/* Setup the timer, when timeout != NULL */
if (unlikely(timeout)) {
hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
if (!hrtimer_active(&timeout->timer))
timeout->task = NULL;
}

for (;;) {
/* Try to acquire the lock: */
if (try_to_take_rt_mutex(lock))
Expand All @@ -656,19 +646,19 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
}

/*
* waiter.task is NULL the first time we come here and
* waiter->task is NULL the first time we come here and
* when we have been woken up by the previous owner
* but the lock got stolen by a higher prio task.
*/
if (!waiter.task) {
ret = task_blocks_on_rt_mutex(lock, &waiter,
if (!waiter->task) {
ret = task_blocks_on_rt_mutex(lock, waiter, current,
detect_deadlock);
/*
* If we got woken up by the owner then start loop
* all over without going into schedule to try
* to get the lock now:
*/
if (unlikely(!waiter.task)) {
if (unlikely(!waiter->task)) {
/*
* Reset the return value. We might
* have returned with -EDEADLK and the
Expand All @@ -684,15 +674,52 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,

spin_unlock(&lock->wait_lock);

debug_rt_mutex_print_deadlock(&waiter);
debug_rt_mutex_print_deadlock(waiter);

if (waiter.task)
if (waiter->task)
schedule_rt_mutex(lock);

spin_lock(&lock->wait_lock);
set_current_state(state);
}

return ret;
}

/*
* Slow path lock function:
*/
static int __sched
rt_mutex_slowlock(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
int detect_deadlock)
{
struct rt_mutex_waiter waiter;
int ret = 0;

debug_rt_mutex_init_waiter(&waiter);
waiter.task = NULL;

spin_lock(&lock->wait_lock);

/* Try to acquire the lock again: */
if (try_to_take_rt_mutex(lock)) {
spin_unlock(&lock->wait_lock);
return 0;
}

set_current_state(state);

/* Setup the timer, when timeout != NULL */
if (unlikely(timeout)) {
hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
if (!hrtimer_active(&timeout->timer))
timeout->task = NULL;
}

ret = __rt_mutex_slowlock(lock, state, timeout, &waiter,
detect_deadlock);

set_current_state(TASK_RUNNING);

if (unlikely(waiter.task))
Expand Down Expand Up @@ -985,6 +1012,59 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
rt_mutex_deadlock_account_unlock(proxy_owner);
}

/**
* rt_mutex_start_proxy_lock() - Start lock acquisition for another task
* @lock: the rt_mutex to take
* @waiter: the pre-initialized rt_mutex_waiter
* @task: the task to prepare
* @detect_deadlock: perform deadlock detection (1) or not (0)
*
* Returns:
* 0 - task blocked on lock
* 1 - acquired the lock for task, caller should wake it up
* <0 - error
*
* Special API call for FUTEX_REQUEUE_PI support.
*/
int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task, int detect_deadlock)
{
int ret;

spin_lock(&lock->wait_lock);

mark_rt_mutex_waiters(lock);

if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
/* We got the lock for task. */
debug_rt_mutex_lock(lock);

rt_mutex_set_owner(lock, task, 0);

rt_mutex_deadlock_account_lock(lock, task);
return 1;
}

ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);


if (ret && !waiter->task) {
/*
* Reset the return value. We might have
* returned with -EDEADLK and the owner
* released the lock while we were walking the
* pi chain. Let the waiter sort it out.
*/
ret = 0;
}
spin_unlock(&lock->wait_lock);

debug_rt_mutex_print_deadlock(waiter);

return ret;
}

/**
* rt_mutex_next_owner - return the next owner of the lock
*
Expand All @@ -1004,3 +1084,57 @@ struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)

return rt_mutex_top_waiter(lock)->task;
}

/**
* rt_mutex_finish_proxy_lock() - Complete lock acquisition
* @lock: the rt_mutex we were woken on
* @to: the timeout, null if none. hrtimer should already have
* been started.
* @waiter: the pre-initialized rt_mutex_waiter
* @detect_deadlock: perform deadlock detection (1) or not (0)
*
* Complete the lock acquisition started our behalf by another thread.
*
* Returns:
* 0 - success
* <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
*
* Special API call for PI-futex requeue support
*/
int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter,
int detect_deadlock)
{
int ret;

spin_lock(&lock->wait_lock);

set_current_state(TASK_INTERRUPTIBLE);

ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter,
detect_deadlock);

set_current_state(TASK_RUNNING);

if (unlikely(waiter->task))
remove_waiter(lock, waiter);

/*
* try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
* have to fix that up.
*/
fixup_rt_mutex_waiters(lock);

spin_unlock(&lock->wait_lock);

/*
* Readjust priority, when we did not get the lock. We might have been
* the pending owner and boosted. Since we did not take the lock, the
* PI boost has to go.
*/
if (unlikely(ret))
rt_mutex_adjust_prio(current);

return ret;
}
8 changes: 8 additions & 0 deletions kernel/rtmutex_common.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -120,6 +120,14 @@ extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
struct task_struct *proxy_owner);
extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
struct task_struct *proxy_owner);
extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task,
int detect_deadlock);
extern int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter,
int detect_deadlock);

#ifdef CONFIG_DEBUG_RT_MUTEXES
# include "rtmutex-debug.h"
Expand Down

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