Question

我已将一个较大的程序提炼到底部显示的代码。在valgrind中运行此程序最终将报告此错误：

==7234== Invalid read of size 4
==7234==    at 0x34A7275FC8: _IO_file_write@@GLIBC_2.2.5 (in /usr/lib64/libc-2.15.so)
==7234==    by 0x34A7275EA1: new_do_write (in /usr/lib64/libc-2.15.so)
==7234==    by 0x34A7276D44: _IO_do_write@@GLIBC_2.2.5 (in /usr/lib64/libc-2.15.so)
==7234==    by 0x34A7278DB6: _IO_flush_all_lockp (in /usr/lib64/libc-2.15.so)
==7234==    by 0x34A7278F07: _IO_cleanup (in /usr/lib64/libc-2.15.so)
==7234==    by 0x34A7238BBF: __run_exit_handlers (in /usr/lib64/libc-2.15.so)
==7234==    by 0x34A7238BF4: exit (in /usr/lib64/libc-2.15.so)
==7234==    by 0x34A722173B: (below main) (in /usr/lib64/libc-2.15.so)
==7234==  Address 0x542f2e0 is 0 bytes inside a block of size 568 free'd
==7234==    at 0x4A079AE: free (vg_replace_malloc.c:427)
==7234==    by 0x34A726B11C: fclose@@GLIBC_2.2.5 (in /usr/lib64/libc-2.15.so)
==7234==    by 0x40087C: writer (t.c:22)
==7234==    by 0x34A7607D13: start_thread (in /usr/lib64/libpthread-2.15.so)
==7234==    by 0x34A72F167C: clone (in /usr/lib64/libc-2.15.so)

从上面的输出中，这似乎正在发生的事情：

main（）返回，并开始运行退出处理程序以关闭所有FILE *
仍在运行的writer（）线程唤醒，关闭FILE *
退出处理程序尝试访问已关闭的FILE *，现在无效/ free（）'d

据我所知，测试程序没有做任何不确定的事情，但我很乐意在这方面做错。

Valgrind挂钩到各种函数，所以它可能是一个valgrind bug而不是glibc。

这是一个glibc bug吗？
或者它是一个valgrind错误？
关于如何确定它是valgrind还是glibc的任何想法？

T.C：

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void *test(void *arg)
{
    return NULL;
}
void *writer(void *arg)
{
    for(;;) {
        char a[100];
        FILE *f = fopen("out", "w");

        if(f == NULL)
           abort();

        fputs("Test", f);

        if(fgets(a, 100, stdin))
            fputs(a, f);
        fclose(f);  //line 22
    }

    return NULL;
}

int main(int argc, char *argv[])
{
    pthread_t tid1,tid2;


    pthread_create(&tid1, NULL, writer, NULL);
    pthread_create(&tid2, NULL, test, NULL);
    pthread_join(tid2, NULL);
    //pthread_join(tid1, NULL); //no bug if we wait for writer()
    return 0;
}
//compile: gcc t.c -g -pthread

可能需要几分钟才能从valgrind触发错误，其中包含：

while [ true ]; do 
  echo test |valgrind --error-exitcode=2 ./a.out  || break  
done

环境：Fedora 17，glibc-2.15，gcc-4.7.0-5，内核3.5.3-1.fc17.x86_64，valgrind-3.7.0-4

glibc，退出时关闭文件*之间可能的竞争条件？

0 个答案: