nuttx/syscall.csv at 15991ef919ccbadaa4083cf1abb66c1ff2d53fe9

Gregory Nutt 8868c58720 Fix Deadloop in VFS if CONFIG_CANCELLATION_POINTS is enabled

If cancellation points are enabled, then the following logic is activated in sem_wait().  This causes ECANCELED to be returned every time that sem_wait is called.

    int sem_wait(FAR sem_t *sem)
    {
      ...

      /* sem_wait() is a cancellation point */

      if (enter_cancellation_point())
        {
    #ifdef CONFIG_CANCELLATION_POINTS
          /* If there is a pending cancellation, then do not perform
           * the wait.  Exit now with ECANCELED.
           */

          errcode = ECANCELED;
          goto errout_with_cancelpt;
    #endif
        }
      ...

Normally this works fine.  sem_wait() is the OS API called by the application and will cancel the thread just before it returns to the application.  Since it is cancellation point, it should never be called from within the OS.

There there is is one perverse cases where sem_wait() may be nested within another cancellation point.  If open() is called, it will attempt to lock a VFS data structure and will eventually call nxmutex_lock().  nxmutex_lock() waits on a semaphore:

   int nxmutex_lock(FAR mutex_t *mutex)
   {
     ...

     for (; ; )
       {
         /* Take the semaphore (perhaps waiting) */

         ret = _SEM_WAIT(&mutex->sem);
         if (ret >= 0)
           {
             mutex->holder = _SCHED_GETTID();
             break;
           }

         ret = _SEM_ERRVAL(ret);
         if (ret != -EINTR && ret != -ECANCELED)
           {
             break;
           }
       }
   ...
}

In the FLAT build, _SEM_WAIT expands to sem_wait().  That causes the error in the logic:  It should always expand to nxsem_wait().  That is because sem_wait() is cancellation point and should never be called from with the OS or the C library internally.

The failure occurs because the cancellation point logic in sem_wait() returns -ECANCELED (via _SEM_ERRVAL) because sem_wait() is nested; it needs to return the -ECANCELED error to the outermost cancellation point which is open() in this case.  Returning -ECANCELED then causes an infinite loop to occur in nxmutex_lock().

The correct behavior in this case is to call nxsem_wait() instead of sem_wait().  nxsem_wait() is identical to sem_wait() except that it is not a cancelation point.  It will return -ECANCELED if the thread is canceled, but only once.  So no infinite loop results.

In addition, an nxsem_wait() system call was added to support the call from nxmutex_lock().

This resolves Issue #9695

2023-07-06 14:20:29 -03:00

18 KiB

Raw Blame History

1	_assert	assert.h		void	FAR const char *	int	FAR const char *	FAR void *
2	accept4	sys/socket.h	defined(CONFIG_NET)	int	int	FAR struct sockaddr *	FAR socklen_t *	int
3	clock_nanosleep	time.h		int	clockid_t	int	FAR const struct timespec *	FAR struct timespec *
4	epoll_ctl	sys/epoll.h		int	int	int	int	FAR struct epoll_event *
5	epoll_wait	sys/epoll.h		int	int	FAR struct epoll_event *	int	int
6	fcntl	fcntl.h		int	int	int	...	int
7	fs_fdopen	nuttx/fs/fs.h	defined(CONFIG_FILE_STREAM)	int	int	int	FAR struct tcb_s *	FAR struct file_struct **
8	ioctl	sys/ioctl.h		int	int	int	...	unsigned long
9	mq_receive	mqueue.h	!defined(CONFIG_DISABLE_MQUEUE)	ssize_t	mqd_t	FAR char *	size_t	FAR unsigned int *
10	mq_send	mqueue.h	!defined(CONFIG_DISABLE_MQUEUE)	int	mqd_t	FAR const char *	size_t	unsigned int
11	open	fcntl.h		int	FAR const char *	int	...	mode_t
12	ppoll	poll.h		int	FAR struct pollfd *	nfds_t	FAR const struct timespec *	FAR const sigset_t *
13	prctl	sys/prctl.h		int	int	...	uintptr_t	uintptr_t
14	pread	unistd.h		ssize_t	int	FAR void *	size_t	off_t
15	pthread_cond_clockwait	pthread.h	!defined(CONFIG_DISABLE_PTHREAD)	int	FAR pthread_cond_t *	FAR pthread_mutex_t *	clockid_t	FAR const struct timespec *
16	pwrite	unistd.h		ssize_t	int	FAR const void *	size_t	off_t
17	recv	sys/socket.h	defined(CONFIG_NET)	ssize_t	int	FAR void *	size_t	int
18	sched_backtrace	sched.h	defined(CONFIG_SCHED_BACKTRACE)	int	pid_t	FAR void **	int	int
19	send	sys/socket.h	defined(CONFIG_NET)	ssize_t	int	FAR const void *	size_t	int
20	sendfile	sys/sendfile.h		ssize_t	int	int	FAR off_t *	size_t
21	socketpair	sys/socket.h	defined(CONFIG_NET)	int	int	int	int	int [2]\|FAR int *
22	timer_settime	time.h	!defined(CONFIG_DISABLE_POSIX_TIMERS)	int	timer_t	int	FAR const struct itimerspec *	FAR struct itimerspec *
23	timerfd_settime	sys/timerfd.h	defined(CONFIG_TIMER_FD)	int	int	int	FAR const struct itimerspec *	FAR struct itimerspec *
24	waitid	sys/wait.h	defined(CONFIG_SCHED_WAITPID) && defined(CONFIG_SCHED_HAVE_PARENT)	int	idtype_t	id_t	FAR siginfo_t *	int

18 KiB Raw Blame History

18 KiB

Raw Blame History