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    SubjectRe: [PATCH] select: fix sys_select to not leak ERESTARTNOHAND to userspace
    Hi Neil,

    We've been having problems with this select patch change.

    Specifically -- previously, when a ptrace attach was done to a task
    blocked in a select() call and that task had a timeout value,
    the task would restart the select() call with an updated timeout value.

    With this patch in place, the task now instead returns EINTR.

    A test that shows this issue is provided below.

    We also confirmed that attaching to a program sitting
    in select() with gdb makes the select get an EINTR, so this
    behavior also shows up in gdb.

    Thank you for your considerations in this matter.

    ------------------- -------------------
    #include <stdio.h>
    #include <sys/time.h>
    #include <sys/types.h>
    #include <unistd.h>
    #include <errno.h>
    #include <stdlib.h>
    #include <string.h>
    #include <ctype.h>
    #include <time.h>
    #include <signal.h>
    #include <sys/wait.h>
    #include <sys/ptrace.h>

    int
    main(int argc, char ** argv) {
    pid_t kid;
    if ((kid = fork()) == 0) {
    int ms_wait = 2000;
    int rval;
    struct timeval timeout;

    timeout.tv_sec = ms_wait / 1000;
    timeout.tv_usec = (ms_wait % 1000) * 1000;
    rval = select(0, NULL, NULL, NULL, &timeout);
    if (rval == -1) {
    int errcode = errno;
    printf("Hey! Why did my select error off with errno %d (%s)?\n",
    errcode, strerror(errcode));
    fflush(stdout);
    } else {
    printf("select call completed, return value: %d\n", rval);
    }
    exit(0);
    } else if (kid == (pid_t)-1) {
    perror("fork");
    } else {
    int ms_wait = 500;
    int rval;
    struct timeval timeout;

    /* Wait a bit to make sure kid has a chance to get into its
    * select call
    */
    timeout.tv_sec = ms_wait / 1000;
    timeout.tv_usec = (ms_wait % 1000) * 1000;
    rval = select(0, NULL, NULL, NULL, &timeout);

    /* Now attach to the kid, then continue him.
    */
    if (ptrace(PTRACE_ATTACH, kid, (void *)0, (void *)0) != 0) {
    perror("ptrace");
    }
    if (waitpid(kid, &rval, 0) != kid) {
    perror("waitpid");
    }
    if (ptrace(PTRACE_CONT, kid, (void *)0, (void *)0) != 0) {
    perror("ptrace");
    }
    if (waitpid(kid, &rval, 0) != kid) {
    perror("waitpid");
    }
    }
    return 0;
    }
    -
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