Linux学习笔记：pthread_getschedparam函数

在工作中遇到了一个问题，在Linux2.4.*的系统中调用pthread_getschedparam函数时，第一个参数指定为0系统不宕，而在Linux2.6的内核中调用该函数，第一个参数指定为0，则系统宕，原因是收到了SIGSEVG信号，也就是说程序访问的非法的地址。查了一晚上，应该是找到原因了。首先看pthread_getschedparam函数的定义。/*
* sched_getschedparam.c
*
* Description:
* POSIX thread functions that deal with thread scheduling.
*
* --------------------------------------------------------------------------
*
*      Pthreads-win32 - POSIX Threads Library for Win32
*      Copyright（C） 1998 John E. Bossom
*      Copyright（C） 1999,2005 Pthreads-win32 contributors
*
*      Contact Email: rpj@callisto.canberra.edu.au
*
*      The current list of contributors is contained
*      in the file CONTRIBUTORS included with the source
*      code distribution. The list can also be seen at the
*      following World Wide Web location:
*      http://sources.RedHat.com/pthreads-win32/contributors.html
*
*      This library is free software; you can redistribute it and/or
*      modify it under the terms of the GNU Lesser General Public
*      License as published by the Free Software Foundation; either
*      version 2 of the License, or （at your option） any later version.
*
*      This library is distributed in the hope that it will be useful,
*      but WITHOUT ANY WARRANTY; without even the implied warranty of
*      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
*      Lesser General Public License for more details.
*
*      You should have received a copy of the GNU Lesser General Public
*      License along with this library in the file COPYING.LIB;
*     if not, write to the Free Software Foundation, Inc.,
*      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/

#include "pthread.h"
#include "implement.h"
#include "sched.h"

int
pthread_getschedparam （pthread_t thread, int *policy,
       struct sched_param *param）
{
int result;

/* Validate the thread id. */
result = pthread_kill （thread, 0）;
if （0 ！= result）
    {
      return result;
    }

/*
   * Validate the policy and param args.
* Check that a policy constant wasn"t passed rather than &policy.
   */
if （policy <= （int *） SCHED_MAX || param == NULL）
    {
      return EINVAL;
    }

/* Fill out the policy. */
*policy = SCHED_OTHER;

/*
   * This function must return the priority value set by
   * the most recent pthread_setschedparam（） or pthread_create（）
   * for the target thread. It must not return the actual thread
   * priority as altered by any system priority adjustments etc.
   */
param->sched_priority = （（ptw32_thread_t *）thread.p）->sched_priority;

return 0;
}
函数首先调用了pthread_kill函数，在查一下pthread_kill的定义。

/** Copyright （C） 2002, 2003, 2004, 2006 Free Software Foundation, Inc.

`02`	`This file is part of the GNU C Library.`

`03`	`Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.`

04

`05`	`The GNU C Library is free software; you can redistribute it and/or`

`06`	`modify it under the terms of the GNU Lesser General Public`

`07`	`License as published by the Free Software Foundation; either`

`08`	`version 2.1 of the License, or （at your option） any later version.`

09

`10`	`The GNU C Library is distributed in the hope that it will be useful,`

`11`	`but WITHOUT ANY WARRANTY; without even the implied warranty of`

`12`	`MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU`

`13`	`Lesser General Public License for more details.`

14

`15`	`You should have received a copy of the GNU Lesser General Public`

`16`	`License along with the GNU C Library; if not, write to the Free`

`17`	`Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA`

`18`	`02111-1307 USA. */`

19

`20`	`#include <errno.h>`

`21`	`#include <signal.h>`

`22`	`#include <pthreadP.h>`

`23`	`#include <tls.h>`

`24`	`#include <sysdep.h>`

`25`	`#include <kernel-features.h>`

26

27

28 int

`29`	`__pthread_kill （threadid, signo）`

`30`	`pthread_t threadid;`

`31`	`int` `signo;`

32 {

`33`	`struct` `pthread pd = （struct` `pthread ） threadid;`

34

`35`	`/** Make sure the descriptor is valid. */`

`36`	`if` `（DEBUGGING_P && INVALID_TD_P （pd））`

`37`	`/** Not a valid thread handle. */`

`38`	`return` `ESRCH;`

39

`40`	`/** Force load of pd->tid into local variable or register. Otherwise`

`41`	`if a thread exits between ESRCH test and tgkill, we might return`

`42`	`EINVAL, because pd->tid would be cleared by the kernel. */`

`43`	`pid_t tid = atomic_forced_read （pd->tid）;`

`44`	`if` `（__builtin_expect （tid <= 0, 0））`

`45`	`/** Not a valid thread handle. */`

`46`	`return` `ESRCH;`

47

`48`	`/** Disallow sending the signal we use for cancellation, timers, for`

`49`	`for the setxid implementation. */`

`50`	`if` `（signo == SIGCANCEL \|\| signo == SIGTIMER \|\| signo == SIGSETXID）`

`51`	`return` `EINVAL;`

52

`53`	`/** We have a special syscall to do the work. */`

`54`	`INTERNAL_SYSCALL_DECL （err）;`

55

`56`	`/** One comment: The PID field in the TCB can temporarily be changed`

`57`	`（in fork）. But this must not affect this code here. Since this`

`58`	`function would have to be called while the thread is executing`

`59`	`fork, it would have to happen in a signal handler. But this is`

`60`	`no allowed, pthread_kill is not guaranteed to be async-safe. */`

`61`	`int` `val;`

`62`	`#if __ASSUME_TGKILL`

`63`	`val = INTERNAL_SYSCALL （tgkill, err, 3, THREAD_GETMEM （THREAD_SELF, pid）,`

`64`	`tid, signo）;`

65 #else

`66`	`# ifdef __NR_tgkill`

`67`	`val = INTERNAL_SYSCALL （tgkill, err, 3, THREAD_GETMEM （THREAD_SELF, pid）,`

`68`	`tid, signo）;`

`69`	`if` `（INTERNAL_SYSCALL_ERROR_P （val, err）`

`70`	`&& INTERNAL_SYSCALL_ERRNO （val, err） == ENOSYS）`

71 # endif

`72`	`val = INTERNAL_SYSCALL （tkill, err, 2, tid, signo）;`

73 #endif

74

`75`	`return` `（INTERNAL_SYSCALL_ERROR_P （val, err）`

`76`	`？ INTERNAL_SYSCALL_ERRNO （val, err） : 0）;`

77 }

`78`	`strong_alias （__pthread_kill, pthread_kill）`

从中可以看到，在pthread_kill中，if （DEBUGGING_P && INVALID_TD_P （pd））

`37`	`/** Not a valid thread handle. */`

`38`	`return` `ESRCH;`

首先进行了判断，但是很有可能DEBUGGING_P宏没定义，所以程序就跳了过去，然后再

`43`	`pid_t tid = atomic_forced_read （pd->tid）;`

处访问了NULL指针，所以程序宕了。