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Commit 00ff352c authored by Tim Murray's avatar Tim Murray
Browse files

dumpstate: fix race in waitpid_with_timeout() 

If the child process exits fast enough, then sigtimedwait will never
get a signal and never actually call waitpid. Check to see if the
child process has already died before calling sigtimedwait.

Test: dumpstate_test
Bug: 215574756
Change-Id: I5d0fa5d537e502b2a8254f8d6ba218f3f7161229
parent a4419eb5

cmds/dumpstate/DumpstateUtil.cpp

+16 −1
Original line number Diff line number Diff line
@@ -48,11 +48,26 @@ static bool waitpid_with_timeout(pid_t pid, int timeout_ms, int* status) { 
    sigemptyset(&child_mask);

    sigaddset(&child_mask, SIGCHLD);



    // block SIGCHLD before we check if a process has exited

    if (sigprocmask(SIG_BLOCK, &child_mask, &old_mask) == -1) {

        printf("*** sigprocmask failed: %s\n", strerror(errno));

        return false;

    }



    // if the child has exited already, handle and reset signals before leaving

    pid_t child_pid = waitpid(pid, status, WNOHANG);

    if (child_pid != pid) {

        if (child_pid > 0) {

            printf("*** Waiting for pid %d, got pid %d instead\n", pid, child_pid);

            sigprocmask(SIG_SETMASK, &old_mask, nullptr);

            return false;

        }

    } else {

        sigprocmask(SIG_SETMASK, &old_mask, nullptr);

        return true;

    }



    // wait for a SIGCHLD

    timespec ts;

    ts.tv_sec = MSEC_TO_SEC(timeout_ms);

    ts.tv_nsec = (timeout_ms % 1000) * 1000000;
@@ -76,7 +91,7 @@ static bool waitpid_with_timeout(pid_t pid, int timeout_ms, int* status) { 
        return false;

    }



    pid_t child_pid = waitpid(pid, status, WNOHANG);

    child_pid = waitpid(pid, status, WNOHANG);

    if (child_pid != pid) {

        if (child_pid != -1) {

            printf("*** Waiting for pid %d, got pid %d instead\n", pid, child_pid);