b9b615b425
pthread_cond_wait() should be an atomic operation in the mutex lock/unlock.
Since the sched_lock() has been wrongly deleted in the previous commit,
the context switch will occurred after the mutex was unlocked:
--------------------------------------------------------------------
Task1(Priority 100) | Task2(Priority 101)
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pthread_mutex_lock(mutex); |
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pthread_cond_wait(cond, mutex) |
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| ->enter_critical_section() |
| ->pthread_mutex_give(mutex) | ----> pthread_mutex_lock(mutex); // contex switch to high priority task
| | pthread_cond_signal(cond); // signal before wait
| | <---- pthread_mutex_unlock(mutex); // switch back to original task
| ->pthread_sem_take(cond->sem)| // try to wait the signal, Deadlock.
| ->leave_critical_section() |
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| ->pthread_mutex_take(mutex) |
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pthread_mutex_lock(mutex); |
---------------------------------------------------------------------
This PR will bring back sched_lock()/sched_unlock() to avoid context switch to ensure atomicity
Signed-off-by: chao an <anchao@xiaomi.com>
161 lines
4.1 KiB
C
161 lines
4.1 KiB
C
/****************************************************************************
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* sched/pthread/pthread_condwait.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <unistd.h>
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#include <pthread.h>
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#include <sched.h>
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#include <errno.h>
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#include <debug.h>
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#include <nuttx/cancelpt.h>
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#include "pthread/pthread.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: int pthread_cond_wait
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*
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* Description:
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* A thread can wait for a condition variable to be signalled or broadcast.
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*
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* Input Parameters:
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* None
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*
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* Returned Value:
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* None
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*
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* Assumptions:
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*
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****************************************************************************/
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int pthread_cond_wait(FAR pthread_cond_t *cond, FAR pthread_mutex_t *mutex)
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{
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int status;
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int ret;
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irqstate_t flags;
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sinfo("cond=%p mutex=%p\n", cond, mutex);
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/* pthread_cond_wait() is a cancellation point */
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enter_cancellation_point();
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/* Make sure that non-NULL references were provided. */
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if (cond == NULL || mutex == NULL)
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{
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ret = EINVAL;
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}
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/* Make sure that the caller holds the mutex */
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else if (mutex->pid != nxsched_gettid())
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{
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ret = EPERM;
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}
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else
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{
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#ifndef CONFIG_PTHREAD_MUTEX_UNSAFE
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uint8_t mflags;
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#endif
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#ifdef CONFIG_PTHREAD_MUTEX_TYPES
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uint8_t type;
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int16_t nlocks;
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#endif
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/* Give up the mutex */
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sinfo("Give up mutex / take cond\n");
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flags = enter_critical_section();
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sched_lock();
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mutex->pid = INVALID_PROCESS_ID;
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#ifndef CONFIG_PTHREAD_MUTEX_UNSAFE
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mflags = mutex->flags;
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#endif
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#ifdef CONFIG_PTHREAD_MUTEX_TYPES
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type = mutex->type;
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nlocks = mutex->nlocks;
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#endif
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ret = pthread_mutex_give(mutex);
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/* Take the semaphore. This may be awakened only be a signal (EINTR)
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* or if the thread is canceled (ECANCELED)
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*/
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status = pthread_sem_take(&cond->sem, NULL);
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if (ret == OK)
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{
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/* Report the first failure that occurs */
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ret = status;
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}
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sched_unlock();
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leave_critical_section(flags);
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/* Reacquire the mutex.
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*
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* When cancellation points are enabled, we need to hold the mutex
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* when the pthread is canceled and cleanup handlers, if any, are
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* entered.
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*/
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sinfo("Reacquire mutex...\n");
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status = pthread_mutex_take(mutex, NULL);
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if (ret == OK)
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{
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/* Report the first failure that occurs */
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ret = status;
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}
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/* Did we get the mutex? */
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if (status == OK)
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{
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/* Yes.. Then initialize it properly */
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mutex->pid = nxsched_gettid();
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#ifndef CONFIG_PTHREAD_MUTEX_UNSAFE
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mutex->flags = mflags;
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#endif
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#ifdef CONFIG_PTHREAD_MUTEX_TYPES
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mutex->type = type;
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mutex->nlocks = nlocks;
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#endif
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}
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}
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leave_cancellation_point();
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sinfo("Returning %d\n", ret);
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return ret;
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}
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