Attachment 2959 Details for Bug 6910 – Test program

Test program

clone_getpid_sighandler_bug.c (text/plain), 3.36 KB, created by Michael Kerrisk on 2008-09-22 11:47:13 UTC

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Creator: Michael Kerrisk

Created: 2008-09-22 11:47:13 UTC

Size: 3.36 KB

patch

obsolete

>/*#* clone_getpid_sighandler_bug.c
>
>   As at glibc 2.8, glibc caching of PIDs for getpid() means that
>   if a signal is delivered to the child soon after a clone() (i.e.,
>   before the child has a chance to update the cache), then
>   getpid() in the signal handler inside the child returns the wrong
>   value.
>
>   To test this, this program creates a child process that
>   continuously sends a SIGQUIT signal to the process group.
>   Meanwhile the parent loops creating children that sleep
>   for a moment, and then terminate.  In that time, the SIGQUIT
>   handler will be invoked in the child.  If the getpid() cache
>   has not yet been updated, then it will (occasionally) happen
>   that the values returned by glibc's getpid() and a raw
>   syscall(SYS_getpid) will not match.  When that occurs, the
>   child prints a message noting the mismatch.
>
>   If this program is invoked with any command-line argument, then
>   it uses fork() instead of clone().  This can be used to show that
>   the problem does not occur for fork().
>*/
>/*#**
>   Change history
>
>   22 Sep 08    Initial creation
>*/
>#define _GNU_SOURCE
>#include <signal.h>
>#include <sys/syscall.h>
>#include <sys/wait.h>
>#include <sched.h>
>#include <stdio.h>
>#include <stdlib.h>
>#include <unistd.h>
>
>#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
>                        } while (0)
>
>
>static volatile int loop;
>static volatile int gotSig;
>
>
>static int                      /* Startup function for cloned child */
>childFunc(void *arg)
>{
>    usleep(1000);               /* long ebough to ge a signal */
>    return 0;                   /* Child terminates now */
>} /* childFunc */
>
>
>static void
>handler(int sig)
>{
>    pid_t pid;
>
>    pid = getpid();
>
>    if (getpid() != syscall(SYS_getpid)) {
>        printf("getpid() mismatch (loop=%d): getpid()=%ld; "
>                "syscall(SYS_getpid)=%ld\n",
>                loop,
>                (long) getpid(), (long) syscall(SYS_getpid));
>    }
>    gotSig = 1;
>}
>
>
>int
>main(int argc, char *argv[])
>{
>    const int STACK_SIZE = 65536;       /* Stack size for cloned child */
>    char *stack;                        /* Start of stack buffer */
>    char *stackTop;                     /* End of stack buffer */
>    int flags;
>    struct sigaction sa;
>    int status;
>
>    sa.sa_flags = SA_RESTART;
>    sa.sa_handler = handler;
>    sigemptyset(&sa.sa_mask);
>    if (sigaction(SIGQUIT, &sa, NULL) == -1)
>        errExit("sigaction");
>
>    printf("Before clone getpid() = %ld\n", (long) getpid());
>
>    flags = 0;
>
>    if (fork() == 0) {
>        if (fork() != 0)
>            exit(EXIT_SUCCESS);
>        printf("sigsender PID = %ld\n", (long) getpid());
>        for (;;) 
>            killpg(0, SIGQUIT);
>    }
>    wait(NULL);
>
>    /* Allocate stack for child */
>
>    stack = malloc(STACK_SIZE);
>    if (stack == NULL)
>        errExit("malloc");
>    stackTop = stack + STACK_SIZE;      /* Assume stack grows downwards */
>
>    for (loop = 0; ; loop++) {
>        if (argc == 1) {
>            if (clone(childFunc, stackTop, flags | SIGCHLD, NULL) == -1)
>                errExit("clone");
>        } else {
>            if (fork() == 0) {
>                childFunc(NULL);
>                exit(EXIT_SUCCESS);
>            }
>        }
>
>        if (waitpid(-1, &status, 0) == -1)
>            errExit("waitpid");
>        if (loop % 100000 == 0 && loop > 0)
>            printf("loop %d\n", loop);
>    }
>
>    exit(EXIT_SUCCESS);
>} /* main */

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Attachments on bug 6910: 2959