From 76592db0bde9d4908191c2d7e54af3466ffd4673 Mon Sep 17 00:00:00 2001 From: Norman Maurer Date: Mon, 23 Sep 2019 15:30:42 +0200 Subject: [PATCH] Close eventfd shutdown/wakeup race by closely tracking epoll edges (#9586) Motivation This is another iteration of #9476. Modifications Instead of maintaining a count of all writes performed and then using reads during shutdown to ensure all are accounted for, just set a flag after each write and don't reset it until the corresponding event has been returned from epoll_wait. This requires that while a write is still pending we don't reset wakenUp, i.e. continue to block writes from the wakeup() method. Result Race condition eliminated. Fixes #9362 Co-authored-by: Norman Maurer --- .../src/main/c/netty_epoll_native.c | 57 ++++--------- .../netty/channel/epoll/EpollEventLoop.java | 79 +++++++++++++++---- .../java/io/netty/channel/epoll/Native.java | 11 ++- 3 files changed, 88 insertions(+), 59 deletions(-) diff --git a/transport-native-epoll/src/main/c/netty_epoll_native.c b/transport-native-epoll/src/main/c/netty_epoll_native.c index ee9a0cd0f06c..fda29b589006 100644 --- a/transport-native-epoll/src/main/c/netty_epoll_native.c +++ b/transport-native-epoll/src/main/c/netty_epoll_native.c @@ -197,9 +197,8 @@ static void netty_epoll_native_timerFdSetTime(JNIEnv* env, jclass clazz, jint ti } } -static jint netty_epoll_native_epollWaitNoTimeout(JNIEnv* env, jclass clazz, jint efd, jlong address, jint len, jboolean immediatePoll) { +static jint netty_epoll_native_epollWait(JNIEnv* env, jclass clazz, jint efd, jlong address, jint len, jint timeout) { struct epoll_event *ev = (struct epoll_event*) (intptr_t) address; - const int timeout = immediatePoll ? 0 : -1; int result, err; do { @@ -213,47 +212,23 @@ static jint netty_epoll_native_epollWaitNoTimeout(JNIEnv* env, jclass clazz, jin // This method is deprecated! static jint netty_epoll_native_epollWait0(JNIEnv* env, jclass clazz, jint efd, jlong address, jint len, jint timerFd, jint tvSec, jint tvNsec) { - struct epoll_event *ev = (struct epoll_event*) (intptr_t) address; - int result, err; - if (tvSec == 0 && tvNsec == 0) { // Zeros = poll (aka return immediately). - do { - result = epoll_wait(efd, ev, len, 0); - if (result >= 0) { - return result; - } - } while((err = errno) == EINTR); - } else { - // only reschedule the timer if there is a newer event. - // -1 is a special value used by EpollEventLoop. - if (tvSec != ((jint) -1) && tvNsec != ((jint) -1)) { - struct itimerspec ts; - memset(&ts.it_interval, 0, sizeof(struct timespec)); - ts.it_value.tv_sec = tvSec; - ts.it_value.tv_nsec = tvNsec; - if (timerfd_settime(timerFd, 0, &ts, NULL) < 0) { - netty_unix_errors_throwChannelExceptionErrorNo(env, "timerfd_settime() failed: ", errno); - return -1; - } - } - do { - result = epoll_wait(efd, ev, len, -1); - if (result > 0) { - // Detect timeout, and preserve the epoll_wait API. - if (result == 1 && ev[0].data.fd == timerFd) { - // We assume that timerFD is in ET mode. So we must consume this event to ensure we are notified - // of future timer events because ET mode only notifies a single time until the event is consumed. - uint64_t timerFireCount; - // We don't care what the result is. We just want to consume the wakeup event and reset ET. - result = read(timerFd, &timerFireCount, sizeof(uint64_t)); - return 0; - } - return result; - } - } while((err = errno) == EINTR); + return netty_epoll_native_epollWait(env, clazz, efd, address, len, 0); } - return -err; + // only reschedule the timer if there is a newer event. + // -1 is a special value used by EpollEventLoop. + if (tvSec != ((jint) -1) && tvNsec != ((jint) -1)) { + struct itimerspec ts; + memset(&ts.it_interval, 0, sizeof(struct timespec)); + ts.it_value.tv_sec = tvSec; + ts.it_value.tv_nsec = tvNsec; + if (timerfd_settime(timerFd, 0, &ts, NULL) < 0) { + netty_unix_errors_throwChannelExceptionErrorNo(env, "timerfd_settime() failed: ", errno); + return -1; + } + } + return netty_epoll_native_epollWait(env, clazz, efd, address, len, -1); } static inline void cpu_relax() { @@ -524,7 +499,7 @@ static const JNINativeMethod fixed_method_table[] = { { "timerFdSetTime", "(III)V", (void *) netty_epoll_native_timerFdSetTime }, { "epollCreate", "()I", (void *) netty_epoll_native_epollCreate }, { "epollWait0", "(IJIIII)I", (void *) netty_epoll_native_epollWait0 }, // This method is deprecated! - { "epollWaitNoTimeout", "(IJIZ)I", (void *) netty_epoll_native_epollWaitNoTimeout }, + { "epollWait", "(IJII)I", (void *) netty_epoll_native_epollWait }, { "epollBusyWait0", "(IJI)I", (void *) netty_epoll_native_epollBusyWait0 }, { "epollCtlAdd0", "(III)I", (void *) netty_epoll_native_epollCtlAdd0 }, { "epollCtlMod0", "(III)I", (void *) netty_epoll_native_epollCtlMod0 }, diff --git a/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java b/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java index ffcf48aa6bbd..40c25ac63355 100644 --- a/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java +++ b/transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java @@ -36,7 +36,7 @@ import java.util.BitSet; import java.util.Queue; import java.util.concurrent.Executor; -import java.util.concurrent.atomic.AtomicIntegerFieldUpdater; +import java.util.concurrent.atomic.AtomicInteger; import static java.lang.Math.min; @@ -45,8 +45,6 @@ */ class EpollEventLoop extends SingleThreadEventLoop { private static final InternalLogger logger = InternalLoggerFactory.getInstance(EpollEventLoop.class); - private static final AtomicIntegerFieldUpdater WAKEN_UP_UPDATER = - AtomicIntegerFieldUpdater.newUpdater(EpollEventLoop.class, "wakenUp"); static { // Ensure JNI is initialized by the time this class is loaded by this time! @@ -76,8 +74,8 @@ public int get() throws Exception { return epollWaitNow(); } }; - @SuppressWarnings("unused") // AtomicIntegerFieldUpdater - private volatile int wakenUp; + private final AtomicInteger wakenUp = new AtomicInteger(1); + private boolean pendingWakeup; private volatile int ioRatio = 50; // See http://man7.org/linux/man-pages/man2/timerfd_create.2.html. @@ -180,7 +178,7 @@ NativeDatagramPacketArray cleanDatagramPacketArray() { @Override protected void wakeup(boolean inEventLoop) { - if (!inEventLoop && WAKEN_UP_UPDATER.getAndSet(this, 1) == 0) { + if (!inEventLoop && wakenUp.getAndSet(1) == 0) { // write to the evfd which will then wake-up epoll_wait(...) Native.eventFdWrite(eventFd.intValue(), 1L); } @@ -307,13 +305,18 @@ private int epollWait() throws IOException { } private int epollWaitNow() throws IOException { - return Native.epollWait(epollFd, events, timerFd, 0, 0); + return Native.epollWait(epollFd, events, true); } private int epollBusyWait() throws IOException { return Native.epollBusyWait(epollFd, events); } + private int epollWaitTimeboxed() throws IOException { + // Wait with 1 second "safeguard" timeout + return Native.epollWait(epollFd, events, 1000); + } + @Override protected void run() { for (;;) { @@ -329,11 +332,34 @@ protected void run() { break; case SelectStrategy.SELECT: - if (wakenUp == 1) { - wakenUp = 0; + if (pendingWakeup) { + // We are going to be immediately woken so no need to reset wakenUp + // or check for timerfd adjustment. + strategy = epollWaitTimeboxed(); + if (strategy != 0) { + break; + } + // We timed out so assume that we missed the write event due to an + // abnormally failed syscall (the write itself or a prior epoll_wait) + logger.warn("Missed eventfd write (not seen after > 1 second)"); + pendingWakeup = false; + if (hasTasks()) { + break; + } + // fall-through } - if (!hasTasks()) { - strategy = epollWait(); + + wakenUp.set(0); + try { + if (!hasTasks()) { + strategy = epollWait(); + } + } finally { + // Try get() first to avoid much more expensive CAS in the case we + // were woken via the wakeup() method (submitted task) + if (wakenUp.get() == 1 || wakenUp.getAndSet(1) == 1) { + pendingWakeup = true; + } } // fallthrough default: @@ -417,7 +443,9 @@ private void closeAll() { private void processReady(EpollEventArray events, int ready) { for (int i = 0; i < ready; i ++) { final int fd = events.fd(i); - if (fd == eventFd.intValue() || fd == timerFd.intValue()) { + if (fd == eventFd.intValue()) { + pendingWakeup = false; + } else if (fd == timerFd.intValue()) { // Just ignore as we use ET mode for the eventfd and timerfd. // // See also https://stackoverflow.com/a/12492308/1074097 @@ -479,10 +507,23 @@ private void processReady(EpollEventArray events, int ready) { @Override protected void cleanup() { try { - try { - epollFd.close(); - } catch (IOException e) { - logger.warn("Failed to close the epoll fd.", e); + // Ensure any in-flight wakeup writes have been performed prior to closing eventFd. + while (pendingWakeup) { + try { + int count = epollWaitTimeboxed(); + if (count == 0) { + // We timed-out so assume that the write we're expecting isn't coming + break; + } + for (int i = 0; i < count; i++) { + if (events.fd(i) == eventFd.intValue()) { + pendingWakeup = false; + break; + } + } + } catch (IOException ignore) { + // ignore + } } try { eventFd.close(); @@ -494,6 +535,12 @@ protected void cleanup() { } catch (IOException e) { logger.warn("Failed to close the timer fd.", e); } + + try { + epollFd.close(); + } catch (IOException e) { + logger.warn("Failed to close the epoll fd.", e); + } } finally { // release native memory if (iovArray != null) { diff --git a/transport-native-epoll/src/main/java/io/netty/channel/epoll/Native.java b/transport-native-epoll/src/main/java/io/netty/channel/epoll/Native.java index 40af0e742aa9..300816669b37 100644 --- a/transport-native-epoll/src/main/java/io/netty/channel/epoll/Native.java +++ b/transport-native-epoll/src/main/java/io/netty/channel/epoll/Native.java @@ -107,7 +107,14 @@ public static int epollWait(FileDescriptor epollFd, EpollEventArray events, File } static int epollWait(FileDescriptor epollFd, EpollEventArray events, boolean immediatePoll) throws IOException { - int ready = epollWaitNoTimeout(epollFd.intValue(), events.memoryAddress(), events.length(), immediatePoll); + return epollWait(epollFd, events, immediatePoll ? 0 : -1); + } + + /** + * This uses epoll's own timeout and does not reset/re-arm any timerfd + */ + static int epollWait(FileDescriptor epollFd, EpollEventArray events, int timeoutMillis) throws IOException { + int ready = epollWait(epollFd.intValue(), events.memoryAddress(), events.length(), timeoutMillis); if (ready < 0) { throw newIOException("epoll_wait", ready); } @@ -128,7 +135,7 @@ public static int epollBusyWait(FileDescriptor epollFd, EpollEventArray events) } private static native int epollWait0(int efd, long address, int len, int timerFd, int timeoutSec, int timeoutNs); - private static native int epollWaitNoTimeout(int efd, long address, int len, boolean immediatePoll); + private static native int epollWait(int efd, long address, int len, int timeout); private static native int epollBusyWait0(int efd, long address, int len); public static void epollCtlAdd(int efd, final int fd, final int flags) throws IOException {