| /* |
| * RT-Mutexes: simple blocking mutual exclusion locks with PI support |
| * |
| * started by Ingo Molnar and Thomas Gleixner. |
| * |
| * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
| * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> |
| * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt |
| * Copyright (C) 2006 Esben Nielsen |
| * |
| * See Documentation/rt-mutex-design.txt for details. |
| */ |
| #include <linux/spinlock.h> |
| #include <linux/export.h> |
| #include <linux/sched.h> |
| #include <linux/sched/rt.h> |
| #include <linux/timer.h> |
| |
| #include "rtmutex_common.h" |
| |
| /* |
| * lock->owner state tracking: |
| * |
| * lock->owner holds the task_struct pointer of the owner. Bit 0 |
| * is used to keep track of the "lock has waiters" state. |
| * |
| * 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 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 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 val = (unsigned long)owner; |
| |
| if (rt_mutex_has_waiters(lock)) |
| val |= RT_MUTEX_HAS_WAITERS; |
| |
| lock->owner = (struct task_struct *)val; |
| } |
| |
| static inline void clear_rt_mutex_waiters(struct rt_mutex *lock) |
| { |
| lock->owner = (struct task_struct *) |
| ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS); |
| } |
| |
| static void fixup_rt_mutex_waiters(struct rt_mutex *lock) |
| { |
| if (!rt_mutex_has_waiters(lock)) |
| clear_rt_mutex_waiters(lock); |
| } |
| |
| /* |
| * We can speed up the acquire/release, if the architecture |
| * supports cmpxchg and if there's no debugging state to be set up |
| */ |
| #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES) |
| # define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c) |
| static inline void mark_rt_mutex_waiters(struct rt_mutex *lock) |
| { |
| unsigned long owner, *p = (unsigned long *) &lock->owner; |
| |
| 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); |
| * lock(wait_lock); |
| * mark_rt_mutex_waiters(lock); |
| * |
| * cmpxchg(p, owner, 0) != owner |
| * enqueue_waiter(); |
| * unlock(wait_lock); |
| * lock(wait_lock); |
| * wake waiter(); |
| * unlock(wait_lock); |
| * lock(wait_lock); |
| * acquire(lock); |
| */ |
| return rt_mutex_cmpxchg(lock, owner, NULL); |
| } |
| |
| #else |
| # define rt_mutex_cmpxchg(l,c,n) (0) |
| static inline void mark_rt_mutex_waiters(struct rt_mutex *lock) |
| { |
| lock->owner = (struct task_struct *) |
| ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS); |
| } |
| |
| /* |
| * Simple slow path only version: lock->owner is protected by lock->wait_lock. |
| */ |
| static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock) |
| __releases(lock->wait_lock) |
| { |
| lock->owner = NULL; |
| raw_spin_unlock(&lock->wait_lock); |
| return true; |
| } |
| #endif |
| |
| /* |
| * Calculate task priority from the waiter list priority |
| * |
| * Return task->normal_prio when the waiter list is empty or when |
| * the waiter is not allowed to do priority boosting |
| */ |
| int rt_mutex_getprio(struct task_struct *task) |
| { |
| if (likely(!task_has_pi_waiters(task))) |
| return task->normal_prio; |
| |
| return min(task_top_pi_waiter(task)->pi_list_entry.prio, |
| task->normal_prio); |
| } |
| |
| /* |
| * Adjust the priority of a task, after its pi_waiters got modified. |
| * |
| * This can be both boosting and unboosting. task->pi_lock must be held. |
| */ |
| static void __rt_mutex_adjust_prio(struct task_struct *task) |
| { |
| int prio = rt_mutex_getprio(task); |
| |
| if (task->prio != prio) |
| rt_mutex_setprio(task, prio); |
| } |
| |
| /* |
| * Adjust task priority (undo boosting). Called from the exit path of |
| * rt_mutex_slowunlock() and rt_mutex_slowlock(). |
| * |
| * (Note: We do this outside of the protection of lock->wait_lock to |
| * allow the lock to be taken while or before we readjust the priority |
| * of task. We do not use the spin_xx_mutex() variants here as we are |
| * outside of the debug path.) |
| */ |
| static void rt_mutex_adjust_prio(struct task_struct *task) |
| { |
| unsigned long flags; |
| |
| raw_spin_lock_irqsave(&task->pi_lock, flags); |
| __rt_mutex_adjust_prio(task); |
| raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| } |
| |
| /* |
| * Max number of times we'll walk the boosting chain: |
| */ |
| int max_lock_depth = 1024; |
| |
| static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p) |
| { |
| return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL; |
| } |
| |
| /* |
| * 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 *next_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 -EDEADLK; |
| } |
| 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; |
| |
| /* |
| * We dropped all locks after taking a refcount on @task, so |
| * the task might have moved on in the lock chain or even left |
| * the chain completely and blocks now on an unrelated lock or |
| * on @orig_lock. |
| * |
| * We stored the lock on which @task was blocked in @next_lock, |
| * so we can detect the chain change. |
| */ |
| if (next_lock != waiter->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) { |
| if (!task_has_pi_waiters(task)) |
| goto out_unlock_pi; |
| /* |
| * If deadlock detection is off, we stop here if we |
| * are not the top pi waiter of the task. |
| */ |
| if (!detect_deadlock && 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 the lock is the same as the original |
| * lock which caused us to walk the lock chain or if the |
| * current lock is owned by the task which initiated the chain |
| * walk, we detected a deadlock. |
| */ |
| 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 = -EDEADLK; |
| 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); |
| } |
| |
| /* |
| * Check whether the task which owns the current lock is pi |
| * blocked itself. If yes we store a pointer to the lock for |
| * the lock chain change detection above. After we dropped |
| * task->pi_lock next_lock cannot be dereferenced anymore. |
| */ |
| next_lock = task_blocked_on_lock(task); |
| |
| raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| |
| top_waiter = rt_mutex_top_waiter(lock); |
| raw_spin_unlock(&lock->wait_lock); |
| |
| /* |
| * We reached the end of the lock chain. Stop right here. No |
| * point to go back just to figure that out. |
| */ |
| if (!next_lock) |
| goto out_put_task; |
| |
| 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; |
| } |
| |
| /* |
| * 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; |
| } |
| |
| /* |
| * 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; |
| struct rt_mutex *next_lock; |
| int chain_walk = 0, res; |
| unsigned long flags; |
| |
| /* |
| * Early deadlock detection. We really don't want the task to |
| * enqueue on itself just to untangle the mess later. It's not |
| * only an optimization. We drop the locks, so another waiter |
| * can come in before the chain walk detects the deadlock. So |
| * the other will detect the deadlock and return -EDEADLOCK, |
| * which is wrong, as the other waiter is not in a deadlock |
| * situation. |
| */ |
| if (owner == task) |
| return -EDEADLK; |
| |
| raw_spin_lock_irqsave(&task->pi_lock, flags); |
| __rt_mutex_adjust_prio(task); |
| waiter->task = task; |
| waiter->lock = lock; |
| 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); |
| |
| task->pi_blocked_on = waiter; |
| |
| raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| |
| if (!owner) |
| return 0; |
| |
| raw_spin_lock_irqsave(&owner->pi_lock, flags); |
| if (waiter == rt_mutex_top_waiter(lock)) { |
| 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) |
| chain_walk = 1; |
| } else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) { |
| chain_walk = 1; |
| } |
| |
| /* Store the lock on which owner is blocked or NULL */ |
| next_lock = task_blocked_on_lock(owner); |
| |
| raw_spin_unlock_irqrestore(&owner->pi_lock, flags); |
| /* |
| * Even if full deadlock detection is on, if the owner is not |
| * blocked itself, we can avoid finding this out in the chain |
| * walk. |
| */ |
| if (!chain_walk || !next_lock) |
| 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, |
| next_lock, waiter, task); |
| |
| raw_spin_lock(&lock->wait_lock); |
| |
| return res; |
| } |
| |
| /* |
| * Wake up the next waiter on the lock. |
| * |
| * Remove the top waiter from the current tasks pi 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; |
| unsigned long flags; |
| |
| raw_spin_lock_irqsave(¤t->pi_lock, flags); |
| |
| waiter = rt_mutex_top_waiter(lock); |
| |
| /* |
| * Remove it from current->pi_waiters. We do not adjust a |
| * possible priority boost right now. We execute wakeup in the |
| * boosted mode and go back to normal after releasing |
| * lock->wait_lock. |
| */ |
| plist_del(&waiter->pi_list_entry, ¤t->pi_waiters); |
| |
| /* |
| * As we are waking up the top waiter, and the waiter stays |
| * queued on the lock until it gets the lock, this lock |
| * obviously has waiters. Just set the bit here and this has |
| * the added benefit of forcing all new tasks into the |
| * slow path making sure no task of lower priority than |
| * the top waiter can steal this lock. |
| */ |
| lock->owner = (void *) RT_MUTEX_HAS_WAITERS; |
| |
| raw_spin_unlock_irqrestore(¤t->pi_lock, flags); |
| |
| /* |
| * It's safe to dereference waiter as it cannot go away as |
| * long as we hold lock->wait_lock. The waiter task needs to |
| * acquire it in order to dequeue the waiter. |
| */ |
| wake_up_process(waiter->task); |
| } |
| |
| /* |
| * 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); |
| struct rt_mutex *next_lock = NULL; |
| unsigned long flags; |
| |
| raw_spin_lock_irqsave(¤t->pi_lock, flags); |
| plist_del(&waiter->list_entry, &lock->wait_list); |
| 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); |
| |
| 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); |
| |
| /* Store the lock on which owner is blocked or NULL */ |
| next_lock = task_blocked_on_lock(owner); |
| |
| raw_spin_unlock_irqrestore(&owner->pi_lock, flags); |
| } |
| |
| WARN_ON(!plist_node_empty(&waiter->pi_list_entry)); |
| |
| if (!next_lock) |
| 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, next_lock, NULL, current); |
| |
| raw_spin_lock(&lock->wait_lock); |
| } |
| |
| /* |
| * Recheck the pi chain, in case we got a priority setting |
| * |
| * Called from sched_setscheduler |
| */ |
| void rt_mutex_adjust_pi(struct task_struct *task) |
| { |
| struct rt_mutex_waiter *waiter; |
| struct rt_mutex *next_lock; |
| unsigned long flags; |
| |
| raw_spin_lock_irqsave(&task->pi_lock, flags); |
| |
| waiter = task->pi_blocked_on; |
| if (!waiter || waiter->list_entry.prio == task->prio) { |
| raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| return; |
| } |
| next_lock = waiter->lock; |
| raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| |
| /* gets dropped in rt_mutex_adjust_prio_chain()! */ |
| get_task_struct(task); |
| |
| rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task); |
| } |
| |
| /** |
| * __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 |
| * |
| * 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 ret = 0; |
| |
| for (;;) { |
| /* Try to acquire the lock: */ |
| if (try_to_take_rt_mutex(lock, current, waiter)) |
| break; |
| |
| /* |
| * TASK_INTERRUPTIBLE checks for signals and |
| * timeout. Ignored otherwise. |
| */ |
| if (unlikely(state == TASK_INTERRUPTIBLE)) { |
| /* Signal pending? */ |
| if (signal_pending(current)) |
| ret = -EINTR; |
| if (timeout && !timeout->task) |
| ret = -ETIMEDOUT; |
| if (ret) |
| break; |
| } |
| |
| raw_spin_unlock(&lock->wait_lock); |
| |
| debug_rt_mutex_print_deadlock(waiter); |
| |
| schedule_rt_mutex(lock); |
| |
| raw_spin_lock(&lock->wait_lock); |
| set_current_state(state); |
| } |
| |
| return ret; |
| } |
| |
| static void rt_mutex_handle_deadlock(int res, int detect_deadlock, |
| struct rt_mutex_waiter *w) |
| { |
| /* |
| * If the result is not -EDEADLOCK or the caller requested |
| * deadlock detection, nothing to do here. |
| */ |
| if (res != -EDEADLOCK || detect_deadlock) |
| return; |
| |
| /* |
| * Yell lowdly and stop the task right here. |
| */ |
| rt_mutex_print_deadlock(w); |
| while (1) { |
| set_current_state(TASK_INTERRUPTIBLE); |
| schedule(); |
| } |
| } |
| |
| /* |
| * 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); |
| |
| raw_spin_lock(&lock->wait_lock); |
| |
| /* Try to acquire the lock again: */ |
| if (try_to_take_rt_mutex(lock, current, NULL)) { |
| raw_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 = 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(ret)) { |
| remove_waiter(lock, &waiter); |
| rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter); |
| } |
| |
| /* |
| * try_to_take_rt_mutex() sets the waiter bit |
| * unconditionally. We might have to fix that up. |
| */ |
| fixup_rt_mutex_waiters(lock); |
| |
| raw_spin_unlock(&lock->wait_lock); |
| |
| /* Remove pending timer: */ |
| if (unlikely(timeout)) |
| hrtimer_cancel(&timeout->timer); |
| |
| debug_rt_mutex_free_waiter(&waiter); |
| |
| 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; |
| } |
| |
| /* |
| * Slow path to release a rt-mutex: |
| */ |
| static void __sched |
| rt_mutex_slowunlock(struct rt_mutex *lock) |
| { |
| raw_spin_lock(&lock->wait_lock); |
| |
| debug_rt_mutex_unlock(lock); |
| |
| rt_mutex_deadlock_account_unlock(current); |
| |
| /* |
| * We must be careful here if the fast path is enabled. If we |
| * have no waiters queued we cannot set owner to NULL here |
| * because of: |
| * |
| * foo->lock->owner = NULL; |
| * rtmutex_lock(foo->lock); <- fast path |
| * free = atomic_dec_and_test(foo->refcnt); |
| * rtmutex_unlock(foo->lock); <- fast path |
| * if (free) |
| * kfree(foo); |
| * raw_spin_unlock(foo->lock->wait_lock); |
| * |
| * So for the fastpath enabled kernel: |
| * |
| * Nothing can set the waiters bit as long as we hold |
| * lock->wait_lock. So we do the following sequence: |
| * |
| * owner = rt_mutex_owner(lock); |
| * clear_rt_mutex_waiters(lock); |
| * raw_spin_unlock(&lock->wait_lock); |
| * if (cmpxchg(&lock->owner, owner, 0) == owner) |
| * return; |
| * goto retry; |
| * |
| * The fastpath disabled variant is simple as all access to |
| * lock->owner is serialized by lock->wait_lock: |
| * |
| * lock->owner = NULL; |
| * raw_spin_unlock(&lock->wait_lock); |
| */ |
| while (!rt_mutex_has_waiters(lock)) { |
| /* Drops lock->wait_lock ! */ |
| if (unlock_rt_mutex_safe(lock) == true) |
| return; |
| /* Relock the rtmutex and try again */ |
| raw_spin_lock(&lock->wait_lock); |
| } |
| |
| /* |
| * The wakeup next waiter path does not suffer from the above |
| * race. See the comments there. |
| */ |
| wakeup_next_waiter(lock); |
| |
| raw_spin_unlock(&lock->wait_lock); |
| |
| /* Undo pi boosting if necessary: */ |
| rt_mutex_adjust_prio(current); |
| } |
| |
| /* |
| * debug aware fast / slowpath lock,trylock,unlock |
| * |
| * The atomic acquire/release ops are compiled away, when either the |
| * architecture does not support cmpxchg or when debugging is enabled. |
| */ |
| static inline int |
| rt_mutex_fastlock(struct rt_mutex *lock, int state, |
| int detect_deadlock, |
| int (*slowfn)(struct rt_mutex *lock, int state, |
| struct hrtimer_sleeper *timeout, |
| int detect_deadlock)) |
| { |
| if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) { |
| rt_mutex_deadlock_account_lock(lock, current); |
| return 0; |
| } else |
| return slowfn(lock, state, NULL, detect_deadlock); |
| } |
| |
| static inline int |
| rt_mutex_timed_fastlock(struct rt_mutex *lock, int state, |
| struct hrtimer_sleeper *timeout, int detect_deadlock, |
| int (*slowfn)(struct rt_mutex *lock, int state, |
| struct hrtimer_sleeper *timeout, |
| int detect_deadlock)) |
| { |
| if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) { |
| rt_mutex_deadlock_account_lock(lock, current); |
| return 0; |
| } else |
| return slowfn(lock, state, timeout, detect_deadlock); |
| } |
| |
| static inline int |
| rt_mutex_fasttrylock(struct rt_mutex *lock, |
| int (*slowfn)(struct rt_mutex *lock)) |
| { |
| if (likely(rt_mutex_cmpxchg(lock, NULL, current))) { |
| rt_mutex_deadlock_account_lock(lock, current); |
| return 1; |
| } |
| return slowfn(lock); |
| } |
| |
| static inline void |
| rt_mutex_fastunlock(struct rt_mutex *lock, |
| void (*slowfn)(struct rt_mutex *lock)) |
| { |
| if (likely(rt_mutex_cmpxchg(lock, current, NULL))) |
| rt_mutex_deadlock_account_unlock(current); |
| else |
| slowfn(lock); |
| } |
| |
| /** |
| * rt_mutex_lock - lock a rt_mutex |
| * |
| * @lock: the rt_mutex to be locked |
| */ |
| void __sched rt_mutex_lock(struct rt_mutex *lock) |
| { |
| might_sleep(); |
| |
| rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock); |
| } |
| EXPORT_SYMBOL_GPL(rt_mutex_lock); |
| |
| /** |
| * rt_mutex_lock_interruptible - lock a rt_mutex interruptible |
| * |
| * @lock: the rt_mutex to be locked |
| * @detect_deadlock: deadlock detection on/off |
| * |
| * Returns: |
| * 0 on success |
| * -EINTR when interrupted by a signal |
| * -EDEADLK when the lock would deadlock (when deadlock detection is on) |
| */ |
| int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock, |
| int detect_deadlock) |
| { |
| might_sleep(); |
| |
| return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, |
| detect_deadlock, rt_mutex_slowlock); |
| } |
| EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible); |
| |
| /** |
| * rt_mutex_timed_lock - lock a rt_mutex interruptible |
| * the timeout structure is provided |
| * by the caller |
| * |
| * @lock: the rt_mutex to be locked |
| * @timeout: timeout structure or NULL (no timeout) |
| * @detect_deadlock: deadlock detection on/off |
| * |
| * Returns: |
| * 0 on success |
| * -EINTR when interrupted by a signal |
| * -ETIMEDOUT when the timeout expired |
| * -EDEADLK when the lock would deadlock (when deadlock detection is on) |
| */ |
| int |
| rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout, |
| int detect_deadlock) |
| { |
| might_sleep(); |
| |
| return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout, |
| detect_deadlock, rt_mutex_slowlock); |
| } |
| EXPORT_SYMBOL_GPL(rt_mutex_timed_lock); |
| |
| /** |
| * rt_mutex_trylock - try to lock a rt_mutex |
| * |
| * @lock: the rt_mutex to be locked |
| * |
| * Returns 1 on success and 0 on contention |
| */ |
| int __sched rt_mutex_trylock(struct rt_mutex *lock) |
| { |
| return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock); |
| } |
| EXPORT_SYMBOL_GPL(rt_mutex_trylock); |
| |
| /** |
| * rt_mutex_unlock - unlock a rt_mutex |
| * |
| * @lock: the rt_mutex to be unlocked |
| */ |
| void __sched rt_mutex_unlock(struct rt_mutex *lock) |
| { |
| rt_mutex_fastunlock(lock, rt_mutex_slowunlock); |
| } |
| EXPORT_SYMBOL_GPL(rt_mutex_unlock); |
| |
| /** |
| * rt_mutex_destroy - mark a mutex unusable |
| * @lock: the mutex to be destroyed |
| * |
| * This function marks the mutex uninitialized, and any subsequent |
| * use of the mutex is forbidden. The mutex must not be locked when |
| * this function is called. |
| */ |
| void rt_mutex_destroy(struct rt_mutex *lock) |
| { |
| WARN_ON(rt_mutex_is_locked(lock)); |
| #ifdef CONFIG_DEBUG_RT_MUTEXES |
| lock->magic = NULL; |
| #endif |
| } |
| |
| EXPORT_SYMBOL_GPL(rt_mutex_destroy); |
| |
| /** |
| * __rt_mutex_init - initialize the rt lock |
| * |
| * @lock: the rt lock to be initialized |
| * |
| * Initialize the rt lock to unlocked state. |
| * |
| * Initializing of a locked rt lock is not allowed |
| */ |
| void __rt_mutex_init(struct rt_mutex *lock, const char *name) |
| { |
| lock->owner = NULL; |
| raw_spin_lock_init(&lock->wait_lock); |
| plist_head_init(&lock->wait_list); |
| |
| debug_rt_mutex_init(lock, name); |
| } |
| EXPORT_SYMBOL_GPL(__rt_mutex_init); |
| |
| /** |
| * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a |
| * proxy owner |
| * |
| * @lock: the rt_mutex to be locked |
| * @proxy_owner:the task to set as owner |
| * |
| * No locking. Caller has to do serializing itself |
| * Special API call for PI-futex support |
| */ |
| void rt_mutex_init_proxy_locked(struct rt_mutex *lock, |
| struct task_struct *proxy_owner) |
| { |
| __rt_mutex_init(lock, NULL); |
| debug_rt_mutex_proxy_lock(lock, proxy_owner); |
| rt_mutex_set_owner(lock, proxy_owner); |
| rt_mutex_deadlock_account_lock(lock, proxy_owner); |
| } |
| |
| /** |
| * rt_mutex_proxy_unlock - release a lock on behalf of owner |
| * |
| * @lock: the rt_mutex to be locked |
| * |
| * No locking. Caller has to do serializing itself |
| * Special API call for PI-futex support |
| */ |
| 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); |
| 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; |
| |
| raw_spin_lock(&lock->wait_lock); |
| |
| if (try_to_take_rt_mutex(lock, task, NULL)) { |
| raw_spin_unlock(&lock->wait_lock); |
| return 1; |
| } |
| |
| /* We enforce deadlock detection for futexes */ |
| ret = task_blocks_on_rt_mutex(lock, waiter, task, 1); |
| |
| 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; |
| } |
| |
| /** |
| * rt_mutex_next_owner - return the next owner of the lock |
| * |
| * @lock: the rt lock query |
| * |
| * Returns the next owner of the lock or NULL |
| * |
| * Caller has to serialize against other accessors to the lock |
| * itself. |
| * |
| * Special API call for PI-futex support |
| */ |
| struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock) |
| { |
| if (!rt_mutex_has_waiters(lock)) |
| return NULL; |
| |
| 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; |
| |
| raw_spin_lock(&lock->wait_lock); |
| |
| set_current_state(TASK_INTERRUPTIBLE); |
| |
| ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter); |
| |
| set_current_state(TASK_RUNNING); |
| |
| if (unlikely(ret)) |
| 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); |
| |
| raw_spin_unlock(&lock->wait_lock); |
| |
| return ret; |
| } |