diff options
Diffstat (limited to 'kernel/rtmutex.c')
| -rw-r--r-- | kernel/rtmutex.c | 318 |
1 files changed, 113 insertions, 205 deletions
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c index a960481..ab44911 100644 --- a/kernel/rtmutex.c +++ b/kernel/rtmutex.c @@ -20,41 +20,34 @@ /* * 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 + * is 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 - * - * 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. + * owner bit0 + * NULL 0 lock is free (fast acquire possible) + * NULL 1 lock is free and has waiters and the top waiter + * is going to take the lock* + * taskpointer 0 lock is held (fast release possible) + * taskpointer 1 lock is held and has waiters** * * 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 is 0. + * + * (*) 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. * - * (*) 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. + * (**) There is a small time when bit 0 is set but there are no + * waiters. This can happen when grabbing the lock in the slow path. + * To prevent a cmpxchg of the owner releasing the lock, we need to + * set this bit before looking at the lock. */ 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 +196,14 @@ 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: + * the previous owner of the lock might have released the lock. */ - if (orig_waiter && !orig_waiter->task) + if (orig_waiter && !rt_mutex_owner(orig_lock)) goto out_unlock_pi; /* @@ -254,6 +246,17 @@ 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)) { + /* + * 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 */ @@ -296,78 +299,16 @@ 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 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) +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 +331,52 @@ 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 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, current, 0); + rt_mutex_set_owner(lock, task); - rt_mutex_deadlock_account_lock(lock, current); + rt_mutex_deadlock_account_lock(lock, task); return 1; } @@ -436,6 +414,9 @@ 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 +453,18 @@ 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 and 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(¤t->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 @@ -495,43 +473,19 @@ static void wakeup_next_waiter(struct rt_mutex *lock) * lock->wait_lock. */ plist_del(&waiter->pi_list_entry, ¤t->pi_waiters); - pendowner = waiter->task; - waiter->task = NULL; - rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING); + rt_mutex_set_owner(lock, NULL); raw_spin_unlock_irqrestore(¤t->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); } /* - * Remove a waiter from a lock + * Remove a waiter from a lock and give up * - * Must be called with lock->wait_lock held + * 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) @@ -543,11 +497,13 @@ static void remove_waiter(struct rt_mutex *lock, raw_spin_lock_irqsave(¤t->pi_lock, flags); plist_del(&waiter->list_entry, &lock->wait_list); - waiter->task = NULL; current->pi_blocked_on = NULL; raw_spin_unlock_irqrestore(¤t->pi_lock, flags); - if (first && owner != current) { + if (!owner) + return; + + if (first) { raw_spin_lock_irqsave(&owner->pi_lock, flags); @@ -614,21 +570,19 @@ 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; /* @@ -645,39 +599,11 @@ __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 +624,11 @@ 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 +642,14 @@ 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 +664,6 @@ 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 +681,7 @@ 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 +911,7 @@ 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 +927,7 @@ 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 +953,14 @@ 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 && !rt_mutex_owner(lock)) { /* * Reset the return value. We might have * returned with -EDEADLK and the owner @@ -1056,6 +969,10 @@ 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 +1027,11 @@ 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 +1042,5 @@ 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; } |
