123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173 |
- // Copyright (c) 2013 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #include "base/process/kill.h"
- #include <errno.h>
- #include <signal.h>
- #include <sys/event.h>
- #include <sys/types.h>
- #include <sys/wait.h>
- #include "base/files/file_util.h"
- #include "base/files/scoped_file.h"
- #include "base/logging.h"
- #include "base/posix/eintr_wrapper.h"
- namespace base {
- namespace {
- const int kWaitBeforeKillSeconds = 2;
- // Reap |child| process. This call blocks until completion.
- void BlockingReap(pid_t child) {
- const pid_t result = HANDLE_EINTR(waitpid(child, NULL, 0));
- if (result == -1) {
- DPLOG(ERROR) << "waitpid(" << child << ", NULL, 0)";
- }
- }
- // Waits for |timeout| seconds for the given |child| to exit and reap it. If
- // the child doesn't exit within the time specified, kills it.
- //
- // This function takes two approaches: first, it tries to use kqueue to
- // observe when the process exits. kevent can monitor a kqueue with a
- // timeout, so this method is preferred to wait for a specified period of
- // time. Once the kqueue indicates the process has exited, waitpid will reap
- // the exited child. If the kqueue doesn't provide an exit event notification,
- // before the timeout expires, or if the kqueue fails or misbehaves, the
- // process will be mercilessly killed and reaped.
- //
- // A child process passed to this function may be in one of several states:
- // running, terminated and not yet reaped, and (apparently, and unfortunately)
- // terminated and already reaped. Normally, a process will at least have been
- // asked to exit before this function is called, but this is not required.
- // If a process is terminating and unreaped, there may be a window between the
- // time that kqueue will no longer recognize it and when it becomes an actual
- // zombie that a non-blocking (WNOHANG) waitpid can reap. This condition is
- // detected when kqueue indicates that the process is not running and a
- // non-blocking waitpid fails to reap the process but indicates that it is
- // still running. In this event, a blocking attempt to reap the process
- // collects the known-dying child, preventing zombies from congregating.
- //
- // In the event that the kqueue misbehaves entirely, as it might under a
- // EMFILE condition ("too many open files", or out of file descriptors), this
- // function will forcibly kill and reap the child without delay. This
- // eliminates another potential zombie vector. (If you're out of file
- // descriptors, you're probably deep into something else, but that doesn't
- // mean that zombies be allowed to kick you while you're down.)
- //
- // The fact that this function seemingly can be called to wait on a child
- // that's not only already terminated but already reaped is a bit of a
- // problem: a reaped child's pid can be reclaimed and may refer to a distinct
- // process in that case. The fact that this function can seemingly be called
- // to wait on a process that's not even a child is also a problem: kqueue will
- // work in that case, but waitpid won't, and killing a non-child might not be
- // the best approach.
- void WaitForChildToDie(pid_t child, int timeout) {
- DCHECK_GT(child, 0);
- DCHECK_GT(timeout, 0);
- // DON'T ADD ANY EARLY RETURNS TO THIS FUNCTION without ensuring that
- // |child| has been reaped. Specifically, even if a kqueue, kevent, or other
- // call fails, this function should fall back to the last resort of trying
- // to kill and reap the process. Not observing this rule will resurrect
- // zombies.
- int result;
- ScopedFD kq(HANDLE_EINTR(kqueue()));
- if (!kq.is_valid()) {
- DPLOG(ERROR) << "kqueue()";
- } else {
- struct kevent change = {0};
- EV_SET(&change, child, EVFILT_PROC, EV_ADD, NOTE_EXIT, 0, NULL);
- result = HANDLE_EINTR(kevent(kq.get(), &change, 1, NULL, 0, NULL));
- if (result == -1) {
- if (errno != ESRCH) {
- DPLOG(ERROR) << "kevent (setup " << child << ")";
- } else {
- // At this point, one of the following has occurred:
- // 1. The process has died but has not yet been reaped.
- // 2. The process has died and has already been reaped.
- // 3. The process is in the process of dying. It's no longer
- // kqueueable, but it may not be waitable yet either. Mark calls
- // this case the "zombie death race".
- result = HANDLE_EINTR(waitpid(child, NULL, WNOHANG));
- if (result != 0) {
- // A positive result indicates case 1. waitpid succeeded and reaped
- // the child. A result of -1 indicates case 2. The child has already
- // been reaped. In both of these cases, no further action is
- // necessary.
- return;
- }
- // |result| is 0, indicating case 3. The process will be waitable in
- // short order. Fall back out of the kqueue code to kill it (for good
- // measure) and reap it.
- }
- } else {
- // Keep track of the elapsed time to be able to restart kevent if it's
- // interrupted.
- TimeDelta remaining_delta = Seconds(timeout);
- TimeTicks deadline = TimeTicks::Now() + remaining_delta;
- result = -1;
- struct kevent event = {0};
- while (remaining_delta.InMilliseconds() > 0) {
- const struct timespec remaining_timespec = remaining_delta.ToTimeSpec();
- result = kevent(kq.get(), NULL, 0, &event, 1, &remaining_timespec);
- if (result == -1 && errno == EINTR) {
- remaining_delta = deadline - TimeTicks::Now();
- result = 0;
- } else {
- break;
- }
- }
- if (result == -1) {
- DPLOG(ERROR) << "kevent (wait " << child << ")";
- } else if (result > 1) {
- DLOG(ERROR) << "kevent (wait " << child << "): unexpected result "
- << result;
- } else if (result == 1) {
- if ((event.fflags & NOTE_EXIT) &&
- (event.ident == static_cast<uintptr_t>(child))) {
- // The process is dead or dying. This won't block for long, if at
- // all.
- BlockingReap(child);
- return;
- } else {
- DLOG(ERROR) << "kevent (wait " << child
- << "): unexpected event: fflags=" << event.fflags
- << ", ident=" << event.ident;
- }
- }
- }
- }
- // The child is still alive, or is very freshly dead. Be sure by sending it
- // a signal. This is safe even if it's freshly dead, because it will be a
- // zombie (or on the way to zombiedom) and kill will return 0 even if the
- // signal is not delivered to a live process.
- result = kill(child, SIGKILL);
- if (result == -1) {
- DPLOG(ERROR) << "kill(" << child << ", SIGKILL)";
- } else {
- // The child is definitely on the way out now. BlockingReap won't need to
- // wait for long, if at all.
- BlockingReap(child);
- }
- }
- } // namespace
- void EnsureProcessTerminated(Process process) {
- WaitForChildToDie(process.Pid(), kWaitBeforeKillSeconds);
- }
- } // namespace base
|