Re: [PATCH] rtmutex: multiple candidate owners without unrelated boosting

Steven Rostedt
2010-12-15T02:18:41Z

On Tue, 2010-12-14 at 17:04 +0800, Lai Jiangshan wrote:

OK, I was looking at this in a bit more detail (the coffee finally set
in) and I was at first looking to nuke the cand_owner since it is
redundant to cand_seq. But I think we can nuke the cand_seq instead and
use the top_waiter as the decider.

1) it is less racy, as I show below.
2) we don't need to add any new element to the rt_mutex struct. This is
a win, especially for -rt when that struct exists for every spinlock and
mutex in the kernel.

Maybe I'm missing something, but I wrote some comments below.

> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> include/linux/rtmutex.h | 2
> kernel/futex.c | 25 +--
> kernel/rtmutex.c | 339 +++++++++++++++++++-----------------------------
> kernel/rtmutex_common.h | 20 --
> 4 files changed, 155 insertions(+), 231 deletions(-)
> diff --git a/include/linux/rtmutex.h b/include/linux/rtmutex.h
> index 8d522ff..155ddb3 100644
> --- a/include/linux/rtmutex.h
> +++ b/include/linux/rtmutex.h
> @@ -24,11 +24,13 @@ extern int max_lock_depth; /* for sysctl */
> * @wait_lock: spinlock to protect the structure
> * @wait_list: pilist head to enqueue waiters in priority order
> * @owner: the mutex owner
> + * @cand_seq: the sequence number for candidate owners
> */
> struct rt_mutex {
> raw_spinlock_t wait_lock;
> struct plist_head wait_list;
> struct task_struct *owner;
> + unsigned long cand_seq; /* don't need to init it! */

And this.

> #ifdef CONFIG_DEBUG_RT_MUTEXES
> int save_state;
> const char *name, *file;
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 6c683b3..6db2b92 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -778,15 +778,6 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
> new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
>
> /*
> - * This happens when we have stolen the lock and the original
> - * pending owner did not enqueue itself back on the rt_mutex.
> - * Thats not a tragedy. We know that way, that a lock waiter
> - * is on the fly. We make the futex_q waiter the pending owner.
> - */
> - if (!new_owner)
> - new_owner = this->task;
> -
> - /*
> * We pass it to the next owner. (The WAITERS bit is always
> * kept enabled while there is PI state around. We must also
> * preserve the owner died bit.)
> @@ -1508,8 +1499,8 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
>
> /*
> * We are here either because we stole the rtmutex from the
> - * pending owner or we are the pending owner which failed to
> - * get the rtmutex. We have to replace the pending owner TID
> + * candidate owner or we are the candidate owner which failed to
> + * get the rtmutex. We have to replace the candidate owner TID
> * in the user space variable. This must be atomic as we have
> * to preserve the owner died bit here.
> *
> @@ -1560,7 +1551,7 @@ retry:
>
> /*
> * To handle the page fault we need to drop the hash bucket
> - * lock here. That gives the other task (either the pending
> + * lock here. That gives the other task (either the candidate
> * owner itself or the task which stole the rtmutex) the
> * chance to try the fixup of the pi_state. So once we are
> * back from handling the fault we need to check the pi_state
> @@ -1647,18 +1638,20 @@ static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
> /*
> * pi_state is incorrect, some other task did a lock steal and
> * we returned due to timeout or signal without taking the
> - * rt_mutex. Too late. We can access the rt_mutex_owner without
> - * locking, as the other task is now blocked on the hash bucket
> - * lock. Fix the state up.
> + * rt_mutex. Too late.
> */
> + raw_spin_lock(&q->pi_state->pi_mutex.wait_lock);
> owner = rt_mutex_owner(&q->pi_state->pi_mutex);
> + if (!owner)
> + owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
> + raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock);
> ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
> goto out;
> }
>
> /*
> * Paranoia check. If we did not take the lock, then we should not be
> - * the owner, nor the pending owner, of the rt_mutex.
> + * the owner of the rt_mutex.
> */
> if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
> printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
> diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
> index a960481..f5c8065 100644
> --- a/kernel/rtmutex.c
> +++ b/kernel/rtmutex.c
> @@ -20,41 +20,32 @@
> /*
> * lock->owner state tracking:
> *
> - * lock->owner holds the task_struct pointer of the owner. Bit 0 and 1
> - * are used to keep track of the "owner is pending" and "lock has
> - * waiters" state.
> + * lock->owner holds the task_struct pointer of the owner. Bit 0
> + * are used to keep track of the "lock has waiters" state.
> *
> - * owner bit1 bit0
> - * NULL 0 0 lock is free (fast acquire possible)
> - * NULL 0 1 invalid state
> - * NULL 1 0 Transitional State*
> - * NULL 1 1 invalid state
> - * taskpointer 0 0 lock is held (fast release possible)
> - * taskpointer 0 1 task is pending owner
> - * taskpointer 1 0 lock is held and has waiters
> - * taskpointer 1 1 task is pending owner and lock has more waiters
> + * owner bit0
> + * NULL 0 lock is free (fast acquire possible)
> + * NULL 1 lock is free and has waiters and candidate owners*
> + * taskpointer 0 lock is held (fast release possible)
> + * taskpointer 1 lock is held and has waiters
> *
> - * Pending ownership is assigned to the top (highest priority)
> - * waiter of the lock, when the lock is released. The thread is woken
> - * up and can now take the lock. Until the lock is taken (bit 0
> - * cleared) a competing higher priority thread can steal the lock
> - * which puts the woken up thread back on the waiters list.
> + * Candidate ownership is assigned to the top (highest priority) waiter
> + * of the lock, when the lock is released or the top waiter of the lock
> + * is changed. The thread(s) is(are) woken up and can now take the lock.
> *
> * The fast atomic compare exchange based acquire and release is only
> - * possible when bit 0 and 1 of lock->owner are 0.
> + * possible when bit 0 of lock->owner are 0.
> *
> - * (*) There's a small time where the owner can be NULL and the
> - * "lock has waiters" bit is set. This can happen when grabbing the lock.
> - * To prevent a cmpxchg of the owner releasing the lock, we need to set this
> - * bit before looking at the lock, hence the reason this is a transitional
> - * state.
> + * (*) It also can be a transitional state when grabbing the lock
> + * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
> + * we need to set the bit0 before looking at the lock, and the owner may be
> + * NULL in this small time, hence this can be a transitional state.
> */
>
> static void
> -rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
> - unsigned long mask)
> +rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
> {
> - unsigned long val = (unsigned long)owner | mask;
> + unsigned long val = (unsigned long)owner;
>
> if (rt_mutex_has_waiters(lock))
> val |= RT_MUTEX_HAS_WAITERS;
> @@ -203,15 +194,15 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
> * reached or the state of the chain has changed while we
> * dropped the locks.
> */
> - if (!waiter || !waiter->task)
> + 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
> - * and made us the pending owner:
> + * and made us candidate owner:
> */
> - if (orig_waiter && !orig_waiter->task)
> + if (orig_waiter && orig_waiter->cand_owner)
> goto out_unlock_pi;

This is OK.

>
> /*
> @@ -254,6 +245,22 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
>
> /* Release the task */
> raw_spin_unlock_irqrestore(&task->pi_lock, flags);
> + if (!rt_mutex_owner(lock)) {
> + /*
> + * the lock is free and has waiters, set the top waiter
> + * as a new candidate owner when it is not set.
> + */
> + if (top_waiter != rt_mutex_top_waiter(lock)) {
> + top_waiter = rt_mutex_top_waiter(lock);
> + top_waiter->cand_seq = lock->cand_seq;

No need for the cand_seq.

> + if (!top_waiter->cand_owner) {
> + top_waiter->cand_owner = 1;
> + wake_up_process(top_waiter->task);
> + }
> + }
> + raw_spin_unlock(&lock->wait_lock);
> + goto out_put_task;
> + }
> put_task_struct(task);
>
> /* Grab the next task */
> @@ -296,78 +303,16 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
> }
>
> /*
> - * 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;
> -}
> -
> -/*
> * 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.
> + *
> + * @lock: the lock to be acquired.
> + * @task: the task which want to acquire the lock
> + * @waiter: the waiter queued to the lock's wait list. (could be NULL)
> */
> -static int try_to_take_rt_mutex(struct rt_mutex *lock)
> +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
> @@ -390,15 +335,73 @@ 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, current))
> + if (rt_mutex_owner(lock))
> return 0;
>
> + /*
> + * It is a queued waiter.
> + *
> + * Is it a candidate owner? If it is, it will win unconditionally.
> + * And it defeats the other candidate owner(s) (if any) and
> + * steal lock from them.
> + */
> + if (waiter) {
> + /* candidate owner? */
> + if (waiter->cand_owner && waiter->cand_seq == lock->cand_seq)
> + goto get_lock;

I think the below is a better check.

> +
> + /*
> + * top waiter must be a candidate owner.
> + * But checking it again is not a bad thing.
> + */
> + if (waiter == rt_mutex_top_waiter(lock))
> + goto get_lock;

The reason being, is that we could have the following scenario.

task A has lock, and B and C are waiting.

task A lets go of lock and gives it to B which is higher prio than C

task C is boosted and becomes the top_waiter.

before C gets the lock B get boosted too and it is now the top waiter.

Using the top_waiter to decide who gets the lock is better.

> + }
> +
> + /*
> + * Does it defeat the candidate owner(s) and steal lock from them?
> + *
> + * Note: in the rare case of a task is boosted but its waiter has not
> + * been requeued in the lock's wait list yet, thus it can also steal
> + * the lock.
> + */
> + if (rt_mutex_has_waiters(lock)) {
> + if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio)
> + return 0;
> + }
> +
> +get_lock:
> + 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 have) into
> + * task->pi_waiters list and would get boost from it.
> + */
> + 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);
> + __rt_mutex_adjust_prio(task);
> + }
> + raw_spin_unlock_irqrestore(&task->pi_lock, flags);
> + }
> +
> /* We got the lock. */
> debug_rt_mutex_lock(lock);
>
> - rt_mutex_set_owner(lock, current, 0);
> + rt_mutex_set_owner(lock, task);
>
> - rt_mutex_deadlock_account_lock(lock, current);
> + rt_mutex_deadlock_account_lock(lock, task);
>
> return 1;
> }
> @@ -424,6 +427,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
> __rt_mutex_adjust_prio(task);
> waiter->task = task;
> waiter->lock = lock;
> + waiter->cand_owner = 0;
> plist_node_init(&waiter->list_entry, task->prio);
> plist_node_init(&waiter->pi_list_entry, task->prio);
>
> @@ -436,6 +440,9 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
>
> 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);
> plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
> @@ -472,21 +479,19 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
> /*
> * Wake up the next waiter on the lock.
> *
> - * Remove the top waiter from the current tasks waiter list and from
> - * the lock waiter list. Set it as pending owner. Then wake it up.
> + * Remove the top waiter from the current tasks waiter list.
> + * Set it as a candidate owner. Then wake it up.
> *
> * Called with lock->wait_lock held.
> */
> static void wakeup_next_waiter(struct rt_mutex *lock)
> {
> struct rt_mutex_waiter *waiter;
> - struct task_struct *pendowner;
> unsigned long flags;
>
> raw_spin_lock_irqsave(&current->pi_lock, flags);
>
> waiter = rt_mutex_top_waiter(lock);
> - plist_del(&waiter->list_entry, &lock->wait_list);
>
> /*
> * Remove it from current->pi_waiters. We do not adjust a
> @@ -495,37 +500,14 @@ static void wakeup_next_waiter(struct rt_mutex *lock)
> * lock->wait_lock.
> */
> plist_del(&waiter->pi_list_entry, &current->pi_waiters);
> - pendowner = waiter->task;
> - waiter->task = NULL;
> + waiter->cand_owner = 1;
> + waiter->cand_seq = ++lock->cand_seq;

I think we can keep the cand_owner, but get rid of the cand_seq. Because
I think the cand_seq is a bit racier. The top_waiter should be one to
decide which task is the best candidate.

-- Steve

>
> - rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
> + rt_mutex_set_owner(lock, NULL);
>
> raw_spin_unlock_irqrestore(&current->pi_lock, flags);
>
> - /*
> - * Clear the pi_blocked_on variable and enqueue a possible
> - * waiter into the pi_waiters list of the pending owner. This
> - * prevents that in case the pending owner gets unboosted a
> - * waiter with higher priority than pending-owner->normal_prio
> - * is blocked on the unboosted (pending) owner.
> - */
> - raw_spin_lock_irqsave(&pendowner->pi_lock, flags);
> -
> - WARN_ON(!pendowner->pi_blocked_on);
> - WARN_ON(pendowner->pi_blocked_on != waiter);
> - WARN_ON(pendowner->pi_blocked_on->lock != lock);
> -
> - pendowner->pi_blocked_on = NULL;
> -
> - if (rt_mutex_has_waiters(lock)) {
> - struct rt_mutex_waiter *next;
> -
> - next = rt_mutex_top_waiter(lock);
> - plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
> - }
> - raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
> -
> - wake_up_process(pendowner);
> + wake_up_process(waiter->task);
> }
>
> /*
> @@ -543,11 +525,13 @@ static void remove_waiter(struct rt_mutex *lock,
>
> raw_spin_lock_irqsave(&current->pi_lock, flags);
> plist_del(&waiter->list_entry, &lock->wait_list);
> - waiter->task = NULL;
> current->pi_blocked_on = NULL;
> raw_spin_unlock_irqrestore(&current->pi_lock, flags);
>
> - if (first && owner != current) {
> + if (!owner)
> + return;
> +
> + if (first) {
>
> raw_spin_lock_irqsave(&owner->pi_lock, flags);
>
> @@ -614,22 +598,21 @@ void rt_mutex_adjust_pi(struct task_struct *task)
> * 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,
> - struct rt_mutex_waiter *waiter,
> - int detect_deadlock)
> + struct rt_mutex_waiter *waiter)
> {
> int ret = 0;
>
> for (;;) {
> /* Try to acquire the lock: */
> - if (try_to_take_rt_mutex(lock))
> + if (try_to_take_rt_mutex(lock, current, waiter))
> break;
> + waiter->cand_owner = 0;
>
> /*
> * TASK_INTERRUPTIBLE checks for signals and
> @@ -645,39 +628,11 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
> 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 a higher prio task.
> - */
> - 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)) {
> - /*
> - * Reset the return value. We might
> - * have returned with -EDEADLK and the
> - * owner released the lock while we
> - * were walking the pi chain.
> - */
> - ret = 0;
> - continue;
> - }
> - if (unlikely(ret))
> - break;
> - }
> -
> raw_spin_unlock(&lock->wait_lock);
>
> debug_rt_mutex_print_deadlock(waiter);
>
> - if (waiter->task)
> - schedule_rt_mutex(lock);
> + schedule_rt_mutex(lock);
>
> raw_spin_lock(&lock->wait_lock);
> set_current_state(state);
> @@ -698,12 +653,11 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
> int ret = 0;
>
> debug_rt_mutex_init_waiter(&waiter);
> - waiter.task = NULL;
>
> raw_spin_lock(&lock->wait_lock);
>
> /* Try to acquire the lock again: */
> - if (try_to_take_rt_mutex(lock)) {
> + if (try_to_take_rt_mutex(lock, current, NULL)) {
> raw_spin_unlock(&lock->wait_lock);
> return 0;
> }
> @@ -717,12 +671,14 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
> timeout->task = NULL;
> }
>
> - ret = __rt_mutex_slowlock(lock, state, timeout, &waiter,
> - detect_deadlock);
> + ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
> +
> + if (likely(!ret))
> + ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
>
> set_current_state(TASK_RUNNING);
>
> - if (unlikely(waiter.task))
> + if (unlikely(ret))
> remove_waiter(lock, &waiter);
>
> /*
> @@ -737,14 +693,6 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
> if (unlikely(timeout))
> hrtimer_cancel(&timeout->timer);
>
> - /*
> - * 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);
> -
> debug_rt_mutex_free_waiter(&waiter);
>
> return ret;
> @@ -762,7 +710,7 @@ rt_mutex_slowtrylock(struct rt_mutex *lock)
>
> if (likely(rt_mutex_owner(lock) != current)) {
>
> - ret = try_to_take_rt_mutex(lock);
> + ret = try_to_take_rt_mutex(lock, current, NULL);
> /*
> * try_to_take_rt_mutex() sets the lock waiters
> * bit unconditionally. Clean this up.
> @@ -992,7 +940,7 @@ void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
> {
> __rt_mutex_init(lock, NULL);
> debug_rt_mutex_proxy_lock(lock, proxy_owner);
> - rt_mutex_set_owner(lock, proxy_owner, 0);
> + rt_mutex_set_owner(lock, proxy_owner);
> rt_mutex_deadlock_account_lock(lock, proxy_owner);
> }
>
> @@ -1008,7 +956,7 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
> struct task_struct *proxy_owner)
> {
> debug_rt_mutex_proxy_unlock(lock);
> - rt_mutex_set_owner(lock, NULL, 0);
> + rt_mutex_set_owner(lock, NULL);
> rt_mutex_deadlock_account_unlock(proxy_owner);
> }
>
> @@ -1034,20 +982,14 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
>
> 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);
> + if (try_to_take_rt_mutex(lock, task, NULL)) {
> 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) {
> + if (ret && waiter->cand_owner) {
> /*
> * Reset the return value. We might have
> * returned with -EDEADLK and the owner
> @@ -1056,6 +998,10 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
> */
> ret = 0;
> }
> +
> + if (unlikely(ret))
> + remove_waiter(lock, waiter);
> +
> raw_spin_unlock(&lock->wait_lock);
>
> debug_rt_mutex_print_deadlock(waiter);
> @@ -1110,12 +1056,11 @@ int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
>
> set_current_state(TASK_INTERRUPTIBLE);
>
> - ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter,
> - detect_deadlock);
> + ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
>
> set_current_state(TASK_RUNNING);
>
> - if (unlikely(waiter->task))
> + if (unlikely(ret))
> remove_waiter(lock, waiter);
>
> /*
> @@ -1126,13 +1071,5 @@ int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
>
> raw_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;
> }
> diff --git a/kernel/rtmutex_common.h b/kernel/rtmutex_common.h
> index 97a2f81..178d659 100644
> --- a/kernel/rtmutex_common.h
> +++ b/kernel/rtmutex_common.h
> @@ -43,12 +43,16 @@ extern void schedule_rt_mutex_test(struct rt_mutex *lock);
> * @list_entry: pi node to enqueue into the mutex waiters list
> * @pi_list_entry: pi node to enqueue into the mutex owner waiters list
> * @task: task reference to the blocked task
> + * @cand_owner: did it became candidate owner
> + * @cand_seq: sequence number for checking for candidate owner
> */
> struct rt_mutex_waiter {
> struct plist_node list_entry;
> struct plist_node pi_list_entry;
> struct task_struct *task;
> struct rt_mutex *lock;
> + int cand_owner;
> + unsigned long cand_seq;
> #ifdef CONFIG_DEBUG_RT_MUTEXES
> unsigned long ip;
> struct pid *deadlock_task_pid;
> @@ -91,9 +95,8 @@ task_top_pi_waiter(struct task_struct *p)
> /*
> * lock->owner state tracking:
> */
> -#define RT_MUTEX_OWNER_PENDING 1UL
> -#define RT_MUTEX_HAS_WAITERS 2UL
> -#define RT_MUTEX_OWNER_MASKALL 3UL
> +#define RT_MUTEX_HAS_WAITERS 1UL
> +#define RT_MUTEX_OWNER_MASKALL 1UL
>
> static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
> {
> @@ -101,17 +104,6 @@ static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
> ((unsigned long)lock->owner & ~RT_MUTEX_OWNER_MASKALL);
> }
>
> -static inline struct task_struct *rt_mutex_real_owner(struct rt_mutex *lock)
> -{
> - return (struct task_struct *)
> - ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
> -}
> -
> -static inline unsigned long rt_mutex_owner_pending(struct rt_mutex *lock)
> -{
> - return (unsigned long)lock->owner & RT_MUTEX_OWNER_PENDING;
> -}
> -
> /*
> * PI-futex support (proxy locking functions, etc.):
> */
> diff --git a/scripts/rt-tester/check-all.sh b/scripts/rt-tester/check-all.sh
> old mode 100644
> new mode 100755
> diff --git a/scripts/rt-tester/rt-tester.py b/scripts/rt-tester/rt-tester.py
> old mode 100644
> new mode 100755