static void printk_lock(struct rt_mutex *lock, int print_owner)
{
if (lock->name)
// printk(" [%p] {%s}\n",
;
else
// printk(" [%p] {%s:%d}\n",
;
if (print_owner && rt_mutex_owner(lock)) {
;
;
printk_task(rt_mutex_owner(lock));
;
}
}
/*
* Try to take an rt-mutex
*
* This fails
* - when the lock has a real owner
* - when a different pending owner exists and has higher priority than current
*
* Must be called with lock->wait_lock held.
*/
static int try_to_take_rt_mutex(struct rt_mutex *lock)
{
/*
* We have to be careful here if the atomic speedups are
* enabled, such that, when
* - no other waiter is on the lock
* - the lock has been released since we did the cmpxchg
* the lock can be released or taken while we are doing the
* checks and marking the lock with RT_MUTEX_HAS_WAITERS.
*
* The atomic acquire/release aware variant of
* mark_rt_mutex_waiters uses a cmpxchg loop. After setting
* the WAITERS bit, the atomic release / acquire can not
* happen anymore and lock->wait_lock protects us from the
* non-atomic case.
*
* Note, that this might set lock->owner =
* RT_MUTEX_HAS_WAITERS in the case the lock is not contended
* any more. This is fixed up when we take the ownership.
* This is the transitional state explained at the top of this file.
*/
mark_rt_mutex_waiters(lock);
if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
return 0;
/* We got the lock. */
debug_rt_mutex_lock(lock);
rt_mutex_set_owner(lock, current, 0);
rt_mutex_deadlock_account_lock(lock, current);
return 1;
}
/*
* Slow path try-lock function:
*/
static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
{
int ret;
/*
* If the lock already has an owner we fail to get the lock.
* This can be done without taking the @lock->wait_lock as
* it is only being read, and this is a trylock anyway.
*/
if (rt_mutex_owner(lock))
return 0;
/*
* The mutex has currently no owner. Lock the wait lock and
* try to acquire the lock.
*/
raw_spin_lock(&lock->wait_lock);
ret = try_to_take_rt_mutex(lock, current, NULL);
/*
* try_to_take_rt_mutex() sets the lock waiters bit
* unconditionally. Clean this up.
*/
fixup_rt_mutex_waiters(lock);
raw_spin_unlock(&lock->wait_lock);
return ret;
}
static void printk_lock(struct rt_mutex *lock, int print_owner)
{
if (lock->name)
printk(" [%p] {%s}\n",
lock, lock->name);
else
printk(" [%p] {%s:%d}\n",
lock, lock->file, lock->line);
if (print_owner && rt_mutex_owner(lock)) {
printk(".. ->owner: %p\n", lock->owner);
printk(".. held by: ");
printk_task(rt_mutex_owner(lock));
printk("\n");
}
}
/**
* 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;
raw_spin_lock(&lock->wait_lock);
if (try_to_take_rt_mutex(lock, task, NULL)) {
raw_spin_unlock(&lock->wait_lock);
return 1;
}
ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
if (ret && !rt_mutex_owner(lock)) {
/*
* 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;
}
if (unlikely(ret))
remove_waiter(lock, waiter);
raw_spin_unlock(&lock->wait_lock);
debug_rt_mutex_print_deadlock(waiter);
return ret;
}
/*
* Task blocks on lock.
*
* Prepare waiter and propagate pi chain
*
* This must be called with lock->wait_lock held.
*/
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;
raw_spin_lock_irqsave(&task->pi_lock, flags);
__rt_mutex_adjust_prio(task);
waiter->task = task;
waiter->lock = lock;
waiter->prio = task->prio;
/* Get the top priority waiter on the lock */
if (rt_mutex_has_waiters(lock))
top_waiter = rt_mutex_top_waiter(lock);
rt_mutex_enqueue(lock, waiter);
task->pi_blocked_on = waiter;
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
if (!owner)
return 0;
if (waiter == rt_mutex_top_waiter(lock)) {
raw_spin_lock_irqsave(&owner->pi_lock, flags);
rt_mutex_dequeue_pi(owner, top_waiter);
rt_mutex_enqueue_pi(owner, waiter);
__rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on)
chain_walk = 1;
raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
}
else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
chain_walk = 1;
if (!chain_walk)
return 0;
/*
* The owner can't disappear while holding a lock,
* so the owner struct is protected by wait_lock.
* Gets dropped in rt_mutex_adjust_prio_chain()!
*/
get_task_struct(owner);
raw_spin_unlock(&lock->wait_lock);
res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
task);
raw_spin_lock(&lock->wait_lock);
return res;
}
/*
* Task blocks on lock.
*
* Prepare waiter and propagate pi chain
*
* This must be called with lock->wait_lock held.
*/
static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
int detect_deadlock)
{
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex_waiter *top_waiter = waiter;
unsigned long flags;
int boost = 0, res;
spin_lock_irqsave(¤t->pi_lock, flags);
__rt_mutex_adjust_prio(current);
waiter->task = current;
waiter->lock = lock;
plist_node_init(&waiter->list_entry, current->prio);
plist_node_init(&waiter->pi_list_entry, current->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;
spin_unlock_irqrestore(¤t->pi_lock, flags);
if (waiter == rt_mutex_top_waiter(lock)) {
spin_lock_irqsave(&owner->pi_lock, flags);
plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
__rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on) {
boost = 1;
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(owner);
}
spin_unlock_irqrestore(&owner->pi_lock, flags);
}
else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
spin_lock_irqsave(&owner->pi_lock, flags);
if (owner->pi_blocked_on) {
boost = 1;
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(owner);
}
spin_unlock_irqrestore(&owner->pi_lock, flags);
}
if (!boost)
return 0;
spin_unlock(&lock->wait_lock);
res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
current);
spin_lock(&lock->wait_lock);
return res;
}
/*
* Optimization: check if we can steal the lock from the
* assigned pending owner [which might not have taken the
* lock yet]:
*/
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;
unsigned long flags;
if (!rt_mutex_owner_pending(lock))
return 0;
if (pendowner == task)
return 1;
raw_spin_lock_irqsave(&pendowner->pi_lock, flags);
if (task->prio >= pendowner->prio) {
raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
return 0;
}
/*
* Check if a waiter is enqueued on the pending owners
* pi_waiters list. Remove it and readjust pending owners
* priority.
*/
if (likely(!rt_mutex_has_waiters(lock))) {
raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
return 1;
}
/* No chain handling, pending owner is not blocked on anything: */
next = rt_mutex_top_waiter(lock);
plist_del(&next->pi_list_entry, &pendowner->pi_waiters);
__rt_mutex_adjust_prio(pendowner);
raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
/*
* 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
* 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 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 task:
*/
if (likely(next->task != task)) {
raw_spin_lock_irqsave(&task->pi_lock, flags);
plist_add(&next->pi_list_entry, &task->pi_waiters);
__rt_mutex_adjust_prio(task);
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
}
return 1;
}
static void __rt_down_read(struct rw_semaphore *rwsem, int subclass)
{
struct rt_mutex *lock = &rwsem->lock;
rwsem_acquire_read(&rwsem->dep_map, subclass, 0, _RET_IP_);
if (rt_mutex_owner(lock) != current)
rt_mutex_lock(&rwsem->lock);
rwsem->read_depth++;
}
/*
* Remove a waiter from a lock
*
* Must be called with lock->wait_lock held
*/
static void remove_waiter(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
unsigned long flags)
{
int first = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
int chain_walk = 0;
raw_spin_lock(¤t->pi_lock);
plist_del(&waiter->list_entry, &lock->wait_list);
current->pi_blocked_on = NULL;
raw_spin_unlock(¤t->pi_lock);
if (!owner) {
BUG_ON(first);
return;
}
if (first) {
raw_spin_lock(&owner->pi_lock);
plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
if (rt_mutex_has_waiters(lock)) {
struct rt_mutex_waiter *next;
next = rt_mutex_top_waiter(lock);
plist_add(&next->pi_list_entry, &owner->pi_waiters);
}
__rt_mutex_adjust_prio(owner);
if (rt_mutex_real_waiter(owner->pi_blocked_on))
chain_walk = 1;
raw_spin_unlock(&owner->pi_lock);
}
WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
if (!chain_walk)
return;
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(owner);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
raw_spin_lock_irq(&lock->wait_lock);
}
void __lockfunc rt_read_lock(rwlock_t *rwlock)
{
struct rt_mutex *lock = &rwlock->lock;
rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
/*
* recursive read locks succeed when current owns the lock
*/
if (rt_mutex_owner(lock) != current)
__rt_spin_lock(lock);
rwlock->read_depth++;
}
static inline void
rt_spin_lock_fastunlock(struct rt_mutex *lock,
void (*slowfn)(struct rt_mutex *lock))
{
/* Temporary HACK! */
if (unlikely(rt_mutex_owner(lock) != current) && current->in_printk)
/* don't grab locks for printk in atomic */
return;
if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
rt_mutex_deadlock_account_unlock(current);
else
slowfn(lock);
}
/*
* We fill out the fields in the waiter to store the information about
* the deadlock. We print when we return. act_waiter can be NULL in
* case of a remove waiter operation.
*/
void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *act_waiter,
struct rt_mutex *lock)
{
struct task_struct *task;
if (!rt_trace_on || detect || !act_waiter)
return;
task = rt_mutex_owner(act_waiter->lock);
if (task && task != current) {
act_waiter->deadlock_task_pid = task->pid;
act_waiter->deadlock_lock = lock;
}
}
/*
* We fill out the fields in the waiter to store the information about
* the deadlock. We print when we return. act_waiter can be NULL in
* case of a remove waiter operation.
*/
void debug_rt_mutex_deadlock(enum rtmutex_chainwalk chwalk,
struct rt_mutex_waiter *act_waiter,
struct rt_mutex *lock)
{
struct task_struct *task;
if (!debug_locks || chwalk == RT_MUTEX_FULL_CHAINWALK || !act_waiter)
return;
task = rt_mutex_owner(act_waiter->lock);
if (task && task != current) {
act_waiter->deadlock_task_pid = get_pid(task_pid(task));
act_waiter->deadlock_lock = lock;
}
}
/*
* Remove a waiter from a lock and give up
*
* Must be called with lock->wait_lock held and
* have just failed to try_to_take_rt_mutex().
*/
static void remove_waiter(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter)
{
int first = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
unsigned long flags;
int chain_walk = 0;
raw_spin_lock_irqsave(¤t->pi_lock, flags);
rt_mutex_dequeue(lock, waiter);
current->pi_blocked_on = NULL;
raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
if (!owner)
return;
if (first) {
raw_spin_lock_irqsave(&owner->pi_lock, flags);
rt_mutex_dequeue_pi(owner, waiter);
if (rt_mutex_has_waiters(lock)) {
struct rt_mutex_waiter *next;
next = rt_mutex_top_waiter(lock);
rt_mutex_enqueue_pi(owner, next);
}
__rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on)
chain_walk = 1;
raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
}
if (!chain_walk)
return;
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(owner);
raw_spin_unlock(&lock->wait_lock);
rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
raw_spin_lock(&lock->wait_lock);
}
static int adaptive_wait(struct rt_mutex_waiter *waiter,
struct task_struct *orig_owner)
{
for (;;) {
/* Owner changed? Then lets update the original */
if (orig_owner != rt_mutex_owner(waiter->lock))
return 0;
/* Owner went to bed, so should we */
if (!task_is_current(orig_owner))
return 1;
cpu_relax();
}
}
/*
* Remove a waiter from a lock
*
* Must be called with lock->wait_lock held
*/
static void remove_waiter(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter)
{
int first = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
unsigned long flags;
int boost = 0;
spin_lock_irqsave(¤t->pi_lock, flags);
plist_del(&waiter->list_entry, &lock->wait_list);
waiter->task = NULL;
current->pi_blocked_on = NULL;
spin_unlock_irqrestore(¤t->pi_lock, flags);
if (first && owner != current) {
spin_lock_irqsave(&owner->pi_lock, flags);
plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
if (rt_mutex_has_waiters(lock)) {
struct rt_mutex_waiter *next;
next = rt_mutex_top_waiter(lock);
plist_add(&next->pi_list_entry, &owner->pi_waiters);
}
__rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on) {
boost = 1;
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(owner);
}
spin_unlock_irqrestore(&owner->pi_lock, flags);
}
WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
if (!boost)
return;
spin_unlock(&lock->wait_lock);
rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
spin_lock(&lock->wait_lock);
}
int rt_down_read_trylock(struct rw_semaphore *rwsem)
{
struct rt_mutex *lock = &rwsem->lock;
int ret = 1;
/*
* recursive read locks succeed when current owns the rwsem,
* but not when read_depth == 0 which means that the rwsem is
* write locked.
*/
if (rt_mutex_owner(lock) != current)
ret = rt_mutex_trylock(&rwsem->lock);
else if (!rwsem->read_depth)
ret = 0;
if (ret) {
rwsem->read_depth++;
rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
}
return ret;
}
/*
* Slow path try-lock function:
*/
static inline int
rt_mutex_slowtrylock(struct rt_mutex *lock)
{
int ret = 0;
raw_spin_lock(&lock->wait_lock);
if (likely(rt_mutex_owner(lock) != current)) {
ret = try_to_take_rt_mutex(lock, current, NULL);
/*
* try_to_take_rt_mutex() sets the lock waiters
* bit unconditionally. Clean this up.
*/
fixup_rt_mutex_waiters(lock);
}
raw_spin_unlock(&lock->wait_lock);
return ret;
}
int __lockfunc rt_read_trylock(rwlock_t *rwlock)
{
struct rt_mutex *lock = &rwlock->lock;
int ret = 1;
/*
* recursive read locks succeed when current owns the lock,
* but not when read_depth == 0 which means that the lock is
* write locked.
*/
if (rt_mutex_owner(lock) != current)
ret = rt_mutex_trylock(lock);
else if (!rwlock->read_depth)
ret = 0;
if (ret) {
rwlock->read_depth++;
rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
}
return ret;
}
/**
* 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;
raw_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);
raw_spin_unlock(&lock->wait_lock);
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;
}
raw_spin_unlock(&lock->wait_lock);
debug_rt_mutex_print_deadlock(waiter);
return ret;
}
/*
* Slow path try-lock function:
*/
static inline int
rt_mutex_slowtrylock(struct rt_mutex *lock)
{
unsigned long flags;
int ret = 0;
spin_lock_irqsave(&lock->wait_lock, flags);
if (likely(rt_mutex_owner(lock) != current)) {
init_lists(lock);
ret = try_to_take_rt_mutex(lock);
/*
* try_to_take_rt_mutex() sets the lock waiters
* bit unconditionally. Clean this up.
*/
fixup_rt_mutex_waiters(lock);
}
spin_unlock_irqrestore(&lock->wait_lock, flags);
return ret;
}
void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock)
{
TRACE_WARN_ON_LOCKED(!rt_mutex_owner(lock));
}
void debug_rt_mutex_unlock(struct rt_mutex *lock)
{
TRACE_WARN_ON_LOCKED(rt_mutex_owner(lock) != current);
}
/*
* Try to take an rt-mutex
*
* Must be called with lock->wait_lock held.
*
* @lock: the lock to be acquired.
* @task: the task which wants to acquire the lock
* @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
*/
static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
struct rt_mutex_waiter *waiter)
{
/*
* We have to be careful here if the atomic speedups are
* enabled, such that, when
* - no other waiter is on the lock
* - the lock has been released since we did the cmpxchg
* the lock can be released or taken while we are doing the
* checks and marking the lock with RT_MUTEX_HAS_WAITERS.
*
* The atomic acquire/release aware variant of
* mark_rt_mutex_waiters uses a cmpxchg loop. After setting
* the WAITERS bit, the atomic release / acquire can not
* happen anymore and lock->wait_lock protects us from the
* non-atomic case.
*
* Note, that this might set lock->owner =
* RT_MUTEX_HAS_WAITERS in the case the lock is not contended
* any more. This is fixed up when we take the ownership.
* This is the transitional state explained at the top of this file.
*/
mark_rt_mutex_waiters(lock);
if (rt_mutex_owner(lock))
return 0;
/*
* It will get the lock because of one of these conditions:
* 1) there is no waiter
* 2) higher priority than waiters
* 3) it is top waiter
*/
if (rt_mutex_has_waiters(lock)) {
if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) {
if (!waiter || waiter != rt_mutex_top_waiter(lock))
return 0;
}
}
if (waiter || rt_mutex_has_waiters(lock)) {
unsigned long flags;
struct rt_mutex_waiter *top;
raw_spin_lock_irqsave(&task->pi_lock, flags);
/* remove the queued waiter. */
if (waiter) {
plist_del(&waiter->list_entry, &lock->wait_list);
task->pi_blocked_on = NULL;
}
/*
* We have to enqueue the top waiter(if it exists) into
* task->pi_waiters list.
*/
if (rt_mutex_has_waiters(lock)) {
top = rt_mutex_top_waiter(lock);
top->pi_list_entry.prio = top->list_entry.prio;
plist_add(&top->pi_list_entry, &task->pi_waiters);
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
}
/* We got the lock. */
debug_rt_mutex_lock(lock);
rt_mutex_set_owner(lock, task);
rt_mutex_deadlock_account_lock(lock, task);
return 1;
}
/*
* Adjust the priority chain. Also used for deadlock detection.
* Decreases task's usage by one - may thus free the task.
* Returns 0 or -EDEADLK.
*/
static int rt_mutex_adjust_prio_chain(struct task_struct *task,
int deadlock_detect,
struct rt_mutex *orig_lock,
struct rt_mutex_waiter *orig_waiter,
struct task_struct *top_task)
{
struct rt_mutex *lock;
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
int detect_deadlock, ret = 0, depth = 0;
unsigned long flags;
detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
deadlock_detect);
/*
* The (de)boosting is a step by step approach with a lot of
* pitfalls. We want this to be preemptible and we want hold a
* maximum of two locks per step. So we have to check
* carefully whether things change under us.
*/
again:
if (++depth > max_lock_depth) {
static int prev_max;
/*
* Print this only once. If the admin changes the limit,
* print a new message when reaching the limit again.
*/
if (prev_max != max_lock_depth) {
prev_max = max_lock_depth;
printk(KERN_WARNING "Maximum lock depth %d reached "
"task: %s (%d)\n", max_lock_depth,
top_task->comm, task_pid_nr(top_task));
}
put_task_struct(task);
return deadlock_detect ? -EDEADLK : 0;
}
retry:
/*
* Task can not go away as we did a get_task() before !
*/
raw_spin_lock_irqsave(&task->pi_lock, flags);
waiter = task->pi_blocked_on;
/*
* Check whether the end of the boosting chain has been
* reached or the state of the chain has changed while we
* dropped the locks.
*/
if (!waiter)
goto out_unlock_pi;
/*
* Check the orig_waiter state. After we dropped the locks,
* the previous owner of the lock might have released the lock.
*/
if (orig_waiter && !rt_mutex_owner(orig_lock))
goto out_unlock_pi;
/*
* Drop out, when the task has no waiters. Note,
* top_waiter can be NULL, when we are in the deboosting
* mode!
*/
if (top_waiter && (!task_has_pi_waiters(task) ||
top_waiter != task_top_pi_waiter(task)))
goto out_unlock_pi;
/*
* When deadlock detection is off then we check, if further
* priority adjustment is necessary.
*/
if (!detect_deadlock && waiter->list_entry.prio == task->prio)
goto out_unlock_pi;
lock = waiter->lock;
if (!raw_spin_trylock(&lock->wait_lock)) {
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
cpu_relax();
goto retry;
}
/* Deadlock detection */
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
raw_spin_unlock(&lock->wait_lock);
ret = deadlock_detect ? -EDEADLK : 0;
goto out_unlock_pi;
}
top_waiter = rt_mutex_top_waiter(lock);
/* Requeue the waiter */
plist_del(&waiter->list_entry, &lock->wait_list);
waiter->list_entry.prio = task->prio;
plist_add(&waiter->list_entry, &lock->wait_list);
/* Release the task */
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
if (!rt_mutex_owner(lock)) {
/*
* If the requeue above changed the top waiter, then we need
* to wake the new top waiter up to try to get the lock.
*/
if (top_waiter != rt_mutex_top_waiter(lock))
wake_up_process(rt_mutex_top_waiter(lock)->task);
raw_spin_unlock(&lock->wait_lock);
goto out_put_task;
}
put_task_struct(task);
/* Grab the next task */
task = rt_mutex_owner(lock);
get_task_struct(task);
raw_spin_lock_irqsave(&task->pi_lock, flags);
if (waiter == rt_mutex_top_waiter(lock)) {
/* Boost the owner */
plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
waiter->pi_list_entry.prio = waiter->list_entry.prio;
plist_add(&waiter->pi_list_entry, &task->pi_waiters);
__rt_mutex_adjust_prio(task);
} else if (top_waiter == waiter) {
/* Deboost the owner */
plist_del(&waiter->pi_list_entry, &task->pi_waiters);
waiter = rt_mutex_top_waiter(lock);
waiter->pi_list_entry.prio = waiter->list_entry.prio;
plist_add(&waiter->pi_list_entry, &task->pi_waiters);
__rt_mutex_adjust_prio(task);
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
top_waiter = rt_mutex_top_waiter(lock);
raw_spin_unlock(&lock->wait_lock);
if (!detect_deadlock && waiter != top_waiter)
goto out_put_task;
goto again;
out_unlock_pi:
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
out_put_task:
put_task_struct(task);
return ret;
}
/*
* Slow path lock function spin_lock style: this variant is very
* careful not to miss any non-lock wakeups.
*
* The wakeup side uses wake_up_process_mutex, which, combined with
* the xchg code of this function is a transparent sleep/wakeup
* mechanism nested within any existing sleep/wakeup mechanism. This
* enables the seemless use of arbitrary (blocking) spinlocks within
* sleep/wakeup event loops.
*/
static void fastcall noinline __sched
rt_spin_lock_slowlock(struct rt_mutex *lock)
{
struct rt_mutex_waiter waiter;
unsigned long saved_state, state, flags;
debug_rt_mutex_init_waiter(&waiter);
waiter.task = NULL;
spin_lock_irqsave(&lock->wait_lock, flags);
init_lists(lock);
/* Try to acquire the lock again: */
if (try_to_take_rt_mutex(lock)) {
spin_unlock_irqrestore(&lock->wait_lock, flags);
return;
}
BUG_ON(rt_mutex_owner(lock) == current);
/*
* Here we save whatever state the task was in originally,
* we'll restore it at the end of the function and we'll take
* any intermediate wakeup into account as well, independently
* of the lock sleep/wakeup mechanism. When we get a real
* wakeup the task->state is TASK_RUNNING and we change
* saved_state accordingly. If we did not get a real wakeup
* then we return with the saved state.
*/
saved_state = xchg(¤t->state, TASK_UNINTERRUPTIBLE);
for (;;) {
unsigned long saved_flags;
int saved_lock_depth = current->lock_depth;
/* Try to acquire the lock */
if (try_to_take_rt_mutex(lock))
break;
/*
* 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 an higher prio task.
*/
if (!waiter.task) {
task_blocks_on_rt_mutex(lock, &waiter, 0, flags);
/* Wakeup during boost ? */
if (unlikely(!waiter.task))
continue;
}
/*
* Prevent schedule() to drop BKL, while waiting for
* the lock ! We restore lock_depth when we come back.
*/
saved_flags = current->flags & PF_NOSCHED;
current->lock_depth = -1;
current->flags &= ~PF_NOSCHED;
spin_unlock_irqrestore(&lock->wait_lock, flags);
debug_rt_mutex_print_deadlock(&waiter);
schedule_rt_mutex(lock);
spin_lock_irqsave(&lock->wait_lock, flags);
current->flags |= saved_flags;
current->lock_depth = saved_lock_depth;
state = xchg(¤t->state, TASK_UNINTERRUPTIBLE);
if (unlikely(state == TASK_RUNNING))
saved_state = TASK_RUNNING;
}
state = xchg(¤t->state, saved_state);
if (unlikely(state == TASK_RUNNING))
current->state = TASK_RUNNING;
/*
* Extremely rare case, if we got woken up by a non-mutex wakeup,
* and we managed to steal the lock despite us not being the
* highest-prio waiter (due to SCHED_OTHER changing prio), then we
* can end up with a non-NULL waiter.task:
*/
if (unlikely(waiter.task))
remove_waiter(lock, &waiter, flags);
/*
* try_to_take_rt_mutex() sets the waiter bit
* unconditionally. We might have to fix that up:
*/
fixup_rt_mutex_waiters(lock);
spin_unlock_irqrestore(&lock->wait_lock, flags);
debug_rt_mutex_free_waiter(&waiter);
}
do {
owner = *p;
} while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
}
/*
* Safe fastpath aware unlock:
* 1) Clear the waiters bit
* 2) Drop lock->wait_lock
* 3) Try to unlock the lock with cmpxchg
*/
static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock)
__releases(lock->wait_lock)
{
struct task_struct *owner = rt_mutex_owner(lock);
clear_rt_mutex_waiters(lock);
raw_spin_unlock(&lock->wait_lock);
/*
* If a new waiter comes in between the unlock and the cmpxchg
* we have two situations:
*
* unlock(wait_lock);
* lock(wait_lock);
* cmpxchg(p, owner, 0) == owner
* mark_rt_mutex_waiters(lock);
* acquire(lock);
* or:
*
* unlock(wait_lock);
void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock)
{
DEBUG_LOCKS_WARN_ON(!rt_mutex_owner(lock));
}
void debug_rt_mutex_unlock(struct rt_mutex *lock)
{
if (debug_locks)
DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current);
}
