Linux学习笔记:pthread_getschedparam函数
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 |
|
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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 |
|
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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 |
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02111-1307 USA. */ |
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|
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#include <errno.h> |
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#include <signal.h> |
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#include <pthreadP.h> |
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#include <tls.h> |
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#include <sysdep.h> |
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#include <kernel-features.h> |
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|
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|
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int |
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__pthread_kill (threadid, signo) |
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pthread_t threadid; |
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int signo; |
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{ |
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struct pthread *pd = ( struct pthread *) threadid; |
34 |
|
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/** Make sure the descriptor is valid. */ |
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if (DEBUGGING_P && INVALID_TD_P (pd)) |
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/** Not a valid thread handle. */ |
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return ESRCH; |
39 |
|
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/** Force load of pd->tid into local variable or register. Otherwise |
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if a thread exits between ESRCH test and tgkill, we might return |
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EINVAL, because pd->tid would be cleared by the kernel. */ |
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pid_t tid = atomic_forced_read (pd->tid); |
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if (__builtin_expect (tid <= 0, 0)) |
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/** Not a valid thread handle. */ |
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return ESRCH; |
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|
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/** Disallow sending the signal we use for cancellation, timers, for |
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for the setxid implementation. */ |
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if (signo == SIGCANCEL || signo == SIGTIMER || signo == SIGSETXID) |
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return EINVAL; |
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|
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/** We have a special syscall to do the work. */ |
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INTERNAL_SYSCALL_DECL (err); |
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|
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/** One comment: The PID field in the TCB can temporarily be changed |
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(in fork). But this must not affect this code here. Since this |
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function would have to be called while the thread is executing |
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fork, it would have to happen in a signal handler. But this is |
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no allowed, pthread_kill is not guaranteed to be async-safe. */ |
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int val; |
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#if __ASSUME_TGKILL |
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val = INTERNAL_SYSCALL (tgkill, err, 3, THREAD_GETMEM (THREAD_SELF, pid), |
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tid, signo); |
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#else |
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# ifdef __NR_tgkill |
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val = INTERNAL_SYSCALL (tgkill, err, 3, THREAD_GETMEM (THREAD_SELF, pid), |
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tid, signo); |
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if (INTERNAL_SYSCALL_ERROR_P (val, err) |
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&& INTERNAL_SYSCALL_ERRNO (val, err) == ENOSYS) |
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# endif |
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val = INTERNAL_SYSCALL (tkill, err, 2, tid, signo); |
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#endif |
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|
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return (INTERNAL_SYSCALL_ERROR_P (val, err) |
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? INTERNAL_SYSCALL_ERRNO (val, err) : 0); |
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} |
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strong_alias (__pthread_kill, pthread_kill) |
从中可以看到,在pthread_kill中,
if (DEBUGGING_P && INVALID_TD_P (pd))
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/** Not a valid thread handle. */ |
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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
处访问了NULL指针,所以程序宕了。
43
pid_t tid = atomic_forced_read (pd->tid);
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