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pthreads: Add more robustness characteristics: pthread_mutex_lock() and trylock() will now return EOWNERDEAD if the mutex is locked by a thread that no longer exists. Add pthread_mutex_consistent() to recover from this situation.

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This commit is contained in:
Gregory Nutt 2017-03-26 10:35:23 -06:00
parent bacc4e9b93
commit 363403fb1f
8 changed files with 343 additions and 92 deletions
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36
TODO
View file

@ -1,4 +1,4 @@
NuttX TODO List (Last updated March 14, 2017)
NuttX TODO List (Last updated March 26, 2017)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This file summarizes known NuttX bugs, limitations, inconsistencies with
@ -14,7 +14,7 @@ nuttx/:
(1) Memory Management (mm/)
(0) Power Management (drivers/pm)
(3) Signals (sched/signal, arch/)
(2) pthreads (sched/pthread)
(4) pthreads (sched/pthread)
(0) Message Queues (sched/mqueue)
(8) Kernel/Protected Build
(3) C++ Support
@ -346,7 +346,7 @@ o Signals (sched/signal, arch/)
Priority: Low. Even if there are only 31 usable signals, that is still a lot.
o pthreads (sched/pthreads)
^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^^^^^^^^^^^
Title: PTHREAD_PRIO_PROTECT
Description: Extend pthread_mutexattr_setprotocol(). It should support
@ -448,6 +448,36 @@ o pthreads (sched/pthreads)
Status: Not really open. This is just the way it is.
Priority: Nothing additional is planned.
Title: PTHREAD FILES IN WRONG LOCATTION
Description: There are many pthread interface functions in files located in
sched/pthread. These should be moved from that location to
libc/pthread. In the flat build, this really does not matter,
but in the protected build that location means that system calls
are required to access the pthread interface functions.
Status: Open
Priority: Medium-low. Priority may be higher if system call overheade becomes
an issue.
Title: ROBUST MUTEX ATTRIBUTE NOT SUPPORTED
Description: In NuttX, all mutexes are 'robust' in the sense that an attmpt
to lock a mutex will return EOWNDERDEAD if the holder of the
mutex has died. Unlocking of a mutex will fail if the caller
is not the holder of the mutex.
POSIX, however, requires that there be a mutex attribute called
robust that determines which behavior is supported. non-robust
should be the default. NuttX does not support this attribute
and robust behavior is the default and only supported behavior.
The spec is not clear, but I think there there is also missing
logic when the thread exits. I believe that the next highest
prority thread waiting for the mutex should be awakend and
pthread_mutex_lock() should return EOWNERDEAD.
That does not happen now. They will just remain blocked.
Status: Open
Priority: Low. The non-robust behavior is dangerous and really should never
be used.
o Message Queues (sched/mqueue)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

6
include/pthread.h
View file

@ -1,7 +1,7 @@
/********************************************************************************
* include/pthread.h
*
* Copyright (C) 2007-2009, 2011-2012, 2015-2016 Gregory Nutt. All rights reserved.
* Copyright (C) 2007-2009, 2011-2012, 2015-2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
@ -424,6 +424,10 @@ int pthread_mutex_lock(FAR pthread_mutex_t *mutex);
int pthread_mutex_trylock(FAR pthread_mutex_t *mutex);
int pthread_mutex_unlock(FAR pthread_mutex_t *mutex);
/* Make sure that the pthread mutex is in a consistent state */
int pthread_mutex_consistent(FAR pthread_mutex_t *mutex);
/* Operations on condition variables */
int pthread_condattr_init(FAR pthread_condattr_t *attr);

1
sched/pthread/Make.defs
View file

@ -39,6 +39,7 @@ CSRCS += pthread_create.c pthread_exit.c pthread_join.c pthread_detach.c
CSRCS += pthread_yield.c pthread_getschedparam.c pthread_setschedparam.c
CSRCS += pthread_mutexinit.c pthread_mutexdestroy.c
CSRCS += pthread_mutexlock.c pthread_mutextrylock.c pthread_mutexunlock.c
CSRCS += pthread_mutexconsistent.c
CSRCS += pthread_condinit.c pthread_conddestroy.c
CSRCS += pthread_condwait.c pthread_condsignal.c pthread_condbroadcast.c
CSRCS += pthread_barrierinit.c pthread_barrierdestroy.c pthread_barrierwait.c

138
sched/pthread/pthread_mutexconsistent.c Normal file
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@ -0,0 +1,138 @@
/****************************************************************************
* sched/pthread/pthread_mutexconsistent.c
*
* Copyright (C) 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <pthread.h>
#include <sched.h>
#include <assert.h>
#include <errno.h>
#include <nuttx/semaphore.h>
#include "pthread/pthread.h"
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: pthread_mutex_consistent
*
* Description:
* If mutex is a robust mutex in an inconsistent state, the
* pthread_mutex_consistent() function can be used to mark the state
* protected by the mutex referenced by mutex as consistent again.
*
* If an owner of a robust mutex terminates while holding the mutex, the
* mutex becomes inconsistent and the next thread that acquires the mutex
* lock will be notified of the state by the return value EOWNERDEAD.
* In this case, the mutex does not become normally usable again until the
* state is marked consistent.
*
* If the thread which acquired the mutex lock with the return value
* EOWNERDEAD terminates before calling either pthread_mutex_consistent()
* or pthread_mutex_unlock(), the next thread that acquires the mutex lock
* will be notified about the state of the mutex by the return value
* EOWNERDEAD.
*
* The behavior is undefined if the value specified by the mutex argument
* to pthread_mutex_consistent() does not refer to an initialized mutex.
*
* Input Parameters:
* mutex -- a reference to the mutex to be made consistent
*
* Returned Value:
* Upon successful completion, the pthread_mutex_consistent() function
* will return zero. Otherwise, an error value will be returned to
* indicate the error.
*
****************************************************************************/
int pthread_mutex_consistent(FAR pthread_mutex_t *mutex)
{
int ret = EINVAL;
int status;
sinfo("mutex=0x%p\n", mutex);
DEBUGASSERT(mutex != NULL);
if (mutex != NULL)
{
/* Make sure the mutex is stable while we make the following checks. */
sched_lock();
/* Is the mutex available? */
DEBUGASSERT(mutex->pid != 0); /* < 0: available, >0 owned, ==0 error */
if (mutex->pid >= 0)
{
/* No.. Verify that the PID still exists. We may be destroying
* the mutex after cancelling a pthread and the mutex may have
* been in a bad state owned by the dead pthread. NOTE: The
* folling is unspecified behavior (see pthread_mutex_consistent()).
*
* If the holding thread is still valid, then we should be able to
* map its PID to the underlying TCB. That is what sched_gettcb()
* does.
*/
if (sched_gettcb(mutex->pid) == NULL)
{
/* The thread associated with the PID no longer exists */
mutex->pid = -1;
/* Reset the semaphore. This has the same affect as if the
* dead task had called pthread_mutex_unlock().
*/
status = sem_reset((FAR sem_t *)&mutex->sem, 1);
ret = (status != OK) ? get_errno() : OK;
}
}
sched_unlock();
ret = OK;
}
sinfo("Returning %d\n", ret);
return ret;
}

96
sched/pthread/pthread_mutexdestroy.c
View file

@ -1,7 +1,7 @@
/****************************************************************************
* sched/pthread/pthread_mutexdestroy.c
*
* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
* Copyright (C) 2007-2009, 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
@ -46,6 +46,8 @@
#include <errno.h>
#include <debug.h>
#include <nuttx/semaphore.h>
#include "pthread/pthread.h"
/****************************************************************************
@ -70,60 +72,86 @@
int pthread_mutex_destroy(FAR pthread_mutex_t *mutex)
{
int ret = OK;
int ret = EINVAL;
int status;
sinfo("mutex=0x%p\n", mutex);
DEBUGASSERT(mutex != NULL);
if (mutex == NULL)
if (mutex != NULL)
{
ret = EINVAL;
}
else
{
/* Make sure the semaphore is stable while we make the following
* checks
*/
/* Make sure the semaphore is stable while we make the following checks */
sched_lock();
/* Is the semaphore available? */
/* Is the mutex available? */
if (mutex->pid != -1)
if (mutex->pid >= 0)
{
#ifndef CONFIG_DISABLE_SIGNALS
/* Verify that the PID still exists. We may be destroying the
* mutex after cancelling a pthread and the mutex may have been
* in a bad state owned by the dead pthread.
DEBUGASSERT(mutex->pid != 0); /* < 0: available, >0 owned, ==0 error */
/* No.. Verify that the PID still exists. We may be destroying
* the mutex after cancelling a pthread and the mutex may have
* been in a bad state owned by the dead pthread. NOTE: The
* following behavior is unspecified for pthread_mutex_destroy()
* (see pthread_mutex_consistent()).
*
* If the holding thread is still valid, then we should be able to
* map its PID to the underlying TCB. That is what sched_gettcb()
* does.
*/
ret = kill(mutex->pid, 0);
if (ret < 0)
{
/* The thread associated with the PID no longer exists */
if (sched_gettcb(mutex->pid) == NULL)
{
/* The thread associated with the PID no longer exists */
mutex->pid = -1;
mutex->pid = -1;
/* Destroy the semaphore */
/* Reset the semaphore. If threads are were on this
* semaphore, then this will awakened them and make
* destruction of the semaphore impossible here.
*/
status = sem_destroy((FAR sem_t *)&mutex->sem);
ret = (status != OK) ? get_errno() : OK;
status = sem_reset((FAR sem_t *)&mutex->sem, 1);
if (status < 0)
{
ret = -status;
}
/* Check if the reset caused some other thread to lock the
* mutex.
*/
else if (mutex->pid != -1)
{
/* Yes.. then we cannot destroy the mutex now. */
ret = EBUSY;
}
/* Destroy the underlying semaphore */
else
{
status = sem_destroy((FAR sem_t *)&mutex->sem);
ret = (status != OK) ? get_errno() : OK;
}
}
else
{
ret = EBUSY;
}
else
#endif
{
ret = EBUSY;
}
}
else
{
/* Destroy the semaphore */
/* Destroy the semaphore
*
* REVISIT: What if there are threads waiting on the semaphore?
* Perhaps this logic should all sem_reset() first?
*/
status = sem_destroy((FAR sem_t *)&mutex->sem);
if (status != OK)
{
ret = get_errno();
}
ret = ((status != OK) ? get_errno() : OK);
}
sched_unlock();

53
sched/pthread/pthread_mutexlock.c
View file

@ -1,7 +1,7 @@
/****************************************************************************
* sched/pthread/pthread_mutexlock.c
*
* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
* Copyright (C) 2007-2009, 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
@ -42,9 +42,12 @@
#include <unistd.h>
#include <pthread.h>
#include <sched.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
#include <nuttx/sched.h>
#include "pthread/pthread.h"
/****************************************************************************
@ -104,15 +107,12 @@
int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
{
int mypid = (int)getpid();
int ret = OK;
int ret = EINVAL;
sinfo("mutex=0x%p\n", mutex);
DEBUGASSERT(mutex != NULL);
if (!mutex)
{
ret = EINVAL;
}
else
if (mutex != NULL)
{
/* Make sure the semaphore is stable while we make the following
* checks. This all needs to be one atomic action.
@ -120,7 +120,7 @@ int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
sched_lock();
/* Does this task already hold the semaphore? */
/* Does this thread already hold the semaphore? */
if (mutex->pid == mypid)
{
@ -129,9 +129,12 @@ int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
#ifdef CONFIG_MUTEX_TYPES
if (mutex->type == PTHREAD_MUTEX_RECURSIVE)
{
/* Yes... just increment the number of locks held and return success */
/* Yes... just increment the number of locks held and return
* success.
*/
mutex->nlocks++;
ret = OK;
}
else
#endif
@ -139,19 +142,39 @@ int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
/* No, then we would deadlock... return an error (default
* behavior is like PTHREAD_MUTEX_ERRORCHECK)
*
* NOTE: This is non-compliant behavior for the case of a
* NORMAL mutex. In that case, it the deadlock condition should
* not be detected and the thread should be permitted to
* deadlock.
* NOTE: This is the correct behavior for a 'robust', NORMAL
* mutex. Compiant behavior for non-robust mutex should not
* include these checks. In that case, it the deadlock
* condition should not be detected and the thread should be
* permitted to deadlock.
*/
serr("ERROR: Returning EDEADLK\n");
ret = EDEADLK;
}
}
/* The calling thread does not hold the semaphore. The correct
* behavior for the 'robust' mutex is to verify that the holder of the
* mutex is still valid. This is protection from the case
* where the holder of the mutex has exitted without unlocking it.
*/
else if (mutex->pid > 0 && sched_gettcb(mutex->pid) == NULL)
{
DEBUGASSERT(mutex->pid != 0); /* < 0: available, >0 owned, ==0 error */
/* A thread holds the mutex, but there is no such thread. POSIX
* requires that the 'robust' mutex return EOWNERDEAD in this case.
* It is then the caller's responsibility to call pthread_mutx_consistent()
* fo fix the mutex.
*/
ret = EOWNERDEAD;
}
else
{
/* Take the semaphore */
/* Take the underlying semaphore, waiting if necessary */
ret = pthread_takesemaphore((FAR sem_t *)&mutex->sem);
@ -159,7 +182,7 @@ int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
* that we own it.
*/
if (!ret)
if (ret == OK)
{
mutex->pid = mypid;
#ifdef CONFIG_MUTEX_TYPES

90
sched/pthread/pthread_mutextrylock.c
View file

@ -1,7 +1,7 @@
/****************************************************************************
* sched/pthread/pthread_mutextrylock.c
*
* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
* Copyright (C) 2007-2009, 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
@ -43,6 +43,7 @@
#include <pthread.h>
#include <semaphore.h>
#include <sched.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
@ -83,15 +84,13 @@
int pthread_mutex_trylock(FAR pthread_mutex_t *mutex)
{
int ret = OK;
int status;
int ret = EINVAL;
sinfo("mutex=0x%p\n", mutex);
DEBUGASSERT(mutex != NULL);
if (!mutex)
{
ret = EINVAL;
}
else
if (mutex != NULL)
{
int mypid = (int)getpid();
@ -103,7 +102,8 @@ int pthread_mutex_trylock(FAR pthread_mutex_t *mutex)
/* Try to get the semaphore. */
if (sem_trywait((FAR sem_t *)&mutex->sem) == OK)
status = sem_trywait((FAR sem_t *)&mutex->sem);
if (status == OK)
{
/* If we successfully obtained the semaphore, then indicate
* that we own it.
@ -117,33 +117,63 @@ int pthread_mutex_trylock(FAR pthread_mutex_t *mutex)
mutex->nlocks = 1;
}
#endif
ret = OK;
}
/* Was it not available? */
/* sem_trywait failed */
else if (get_errno() == EAGAIN)
{
#ifdef CONFIG_MUTEX_TYPES
/* Check if recursive mutex was locked by ourself. */
if (mutex->type == PTHREAD_MUTEX_RECURSIVE && mutex->pid == mypid)
{
/* Increment the number of locks held and return successfully. */
mutex->nlocks++;
}
else
{
ret = EBUSY;
}
#else
ret = EBUSY;
#endif
}
else
{
ret = EINVAL;
/* Did it fail because the semaphore was not avaialabl? */
int errcode = get_errno();
if (errcode == EAGAIN)
{
#ifdef CONFIG_MUTEX_TYPES
/* Check if recursive mutex was locked by the calling thread. */
if (mutex->type == PTHREAD_MUTEX_RECURSIVE && mutex->pid == mypid)
{
/* Increment the number of locks held and return successfully. */
mutex->nlocks++;
ret = OK;
}
else
#endif
/* The calling thread does not hold the semaphore. The correct
* behavior for the 'robust' mutex is to verify that the holder of
* the mutex is still valid. This is protection from the case
* where the holder of the mutex has exitted without unlocking it.
*/
if (mutex->pid > 0 && sched_gettcb(mutex->pid) == NULL)
{
DEBUGASSERT(mutex->pid != 0); /* < 0: available, >0 owned, ==0 error */
/* A thread holds the mutex, but there is no such thread.
* POSIX requires that the 'robust' mutex return EOWNERDEAD
* in this case. It is then the caller's responsibility to
* call pthread_mutx_consistent() fo fix the mutex.
*/
ret = EOWNERDEAD;
}
/* The mutex is locked by another, active thread */
else
{
ret = EBUSY;
}
}
/* Some other, unhandled error occurred */
else
{
ret = errcode;
}
}
sched_unlock();

15
sched/pthread/pthread_mutexunlock.c
View file

@ -1,7 +1,7 @@
/****************************************************************************
* sched/pthread/pthread_mutexunlock.c
*
* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
* Copyright (C) 2007-2009, 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
@ -80,15 +80,12 @@
int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
{
int ret = OK;
int ret = EINVAL;
sinfo("mutex=0x%p\n", mutex);
DEBUGASSERT(mutex != NULL);
if (!mutex)
{
ret = EINVAL;
}
else
if (mutex != NULL)
{
/* Make sure the semaphore is stable while we make the following
* checks. This all needs to be one atomic action.
@ -108,8 +105,7 @@ int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
* the mutex."
*
* For the case of the non-robust PTHREAD_MUTEX_NORMAL mutex,
* the behavior is undefined. Here we treat that type as though
* it were PTHREAD_MUTEX_ERRORCHECK type and just return an error.
* the behavior is undefined.
*/
serr("ERROR: Holder=%d returning EPERM\n", mutex->pid);
@ -127,6 +123,7 @@ int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
*/
mutex->nlocks--;
ret = OK;
}
#endif