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authorPaton J. Lewis <palewis@adobe.com>2012-10-04 17:13:39 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-06 03:05:00 +0900
commit03a7beb55b9fad363f0dd33e72ccf2d3e1c2a406 (patch)
treee89cb2a2db5645600f28699ebf3b4a98195a3fb3
parenta0a0a7a94c765f7219b57fa3b79389901bb0bc99 (diff)
downloadvexpress-lsk-03a7beb55b9fad363f0dd33e72ccf2d3e1c2a406.tar.gz
epoll: support for disabling items, and a self-test app
Enhanced epoll_ctl to support EPOLL_CTL_DISABLE, which disables an epoll item. If epoll_ctl doesn't return -EBUSY in this case, it is then safe to delete the epoll item in a multi-threaded environment. Also added a new test_epoll self- test app to both demonstrate the need for this feature and test it. Signed-off-by: Paton J. Lewis <palewis@adobe.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Jason Baron <jbaron@redhat.com> Cc: Paul Holland <pholland@adobe.com> Cc: Davide Libenzi <davidel@xmailserver.org> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/eventpoll.c38
-rw-r--r--include/linux/eventpoll.h1
-rw-r--r--tools/testing/selftests/Makefile2
-rw-r--r--tools/testing/selftests/epoll/Makefile11
-rw-r--r--tools/testing/selftests/epoll/test_epoll.c344
5 files changed, 392 insertions, 4 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index cd96649bfe6..da72250ddc1 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -346,7 +346,7 @@ static inline struct epitem *ep_item_from_epqueue(poll_table *p)
/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
static inline int ep_op_has_event(int op)
{
- return op != EPOLL_CTL_DEL;
+ return op == EPOLL_CTL_ADD || op == EPOLL_CTL_MOD;
}
/* Initialize the poll safe wake up structure */
@@ -676,6 +676,34 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
return 0;
}
+/*
+ * Disables a "struct epitem" in the eventpoll set. Returns -EBUSY if the item
+ * had no event flags set, indicating that another thread may be currently
+ * handling that item's events (in the case that EPOLLONESHOT was being
+ * used). Otherwise a zero result indicates that the item has been disabled
+ * from receiving events. A disabled item may be re-enabled via
+ * EPOLL_CTL_MOD. Must be called with "mtx" held.
+ */
+static int ep_disable(struct eventpoll *ep, struct epitem *epi)
+{
+ int result = 0;
+ unsigned long flags;
+
+ spin_lock_irqsave(&ep->lock, flags);
+ if (epi->event.events & ~EP_PRIVATE_BITS) {
+ if (ep_is_linked(&epi->rdllink))
+ list_del_init(&epi->rdllink);
+ /* Ensure ep_poll_callback will not add epi back onto ready
+ list: */
+ epi->event.events &= EP_PRIVATE_BITS;
+ }
+ else
+ result = -EBUSY;
+ spin_unlock_irqrestore(&ep->lock, flags);
+
+ return result;
+}
+
static void ep_free(struct eventpoll *ep)
{
struct rb_node *rbp;
@@ -1020,8 +1048,6 @@ static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
rb_insert_color(&epi->rbn, &ep->rbr);
}
-
-
#define PATH_ARR_SIZE 5
/*
* These are the number paths of length 1 to 5, that we are allowing to emanate
@@ -1787,6 +1813,12 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
} else
error = -ENOENT;
break;
+ case EPOLL_CTL_DISABLE:
+ if (epi)
+ error = ep_disable(ep, epi);
+ else
+ error = -ENOENT;
+ break;
}
mutex_unlock(&ep->mtx);
diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index f4bb378ccf6..41085d0f395 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -25,6 +25,7 @@
#define EPOLL_CTL_ADD 1
#define EPOLL_CTL_DEL 2
#define EPOLL_CTL_MOD 3
+#define EPOLL_CTL_DISABLE 4
/*
* Request the handling of system wakeup events so as to prevent system suspends
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 85baf11e2ac..43480149119 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -1,4 +1,4 @@
-TARGETS = breakpoints kcmp mqueue vm cpu-hotplug memory-hotplug
+TARGETS = breakpoints kcmp mqueue vm cpu-hotplug memory-hotplug epoll
all:
for TARGET in $(TARGETS); do \
diff --git a/tools/testing/selftests/epoll/Makefile b/tools/testing/selftests/epoll/Makefile
new file mode 100644
index 00000000000..19806ed62f5
--- /dev/null
+++ b/tools/testing/selftests/epoll/Makefile
@@ -0,0 +1,11 @@
+# Makefile for epoll selftests
+
+all: test_epoll
+%: %.c
+ gcc -pthread -g -o $@ $^
+
+run_tests: all
+ ./test_epoll
+
+clean:
+ $(RM) test_epoll
diff --git a/tools/testing/selftests/epoll/test_epoll.c b/tools/testing/selftests/epoll/test_epoll.c
new file mode 100644
index 00000000000..e0fcff1e833
--- /dev/null
+++ b/tools/testing/selftests/epoll/test_epoll.c
@@ -0,0 +1,344 @@
+/*
+ * tools/testing/selftests/epoll/test_epoll.c
+ *
+ * Copyright 2012 Adobe Systems Incorporated
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * Paton J. Lewis <palewis@adobe.com>
+ *
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/epoll.h>
+#include <sys/socket.h>
+
+/*
+ * A pointer to an epoll_item_private structure will be stored in the epoll
+ * item's event structure so that we can get access to the epoll_item_private
+ * data after calling epoll_wait:
+ */
+struct epoll_item_private {
+ int index; /* Position of this struct within the epoll_items array. */
+ int fd;
+ uint32_t events;
+ pthread_mutex_t mutex; /* Guards the following variables... */
+ int stop;
+ int status; /* Stores any error encountered while handling item. */
+ /* The following variable allows us to test whether we have encountered
+ a problem while attempting to cancel and delete the associated
+ event. When the test program exits, 'deleted' should be exactly
+ one. If it is greater than one, then the failed test reflects a real
+ world situation where we would have tried to access the epoll item's
+ private data after deleting it: */
+ int deleted;
+};
+
+struct epoll_item_private *epoll_items;
+
+/*
+ * Delete the specified item from the epoll set. In a real-world secneario this
+ * is where we would free the associated data structure, but in this testing
+ * environment we retain the structure so that we can test for double-deletion:
+ */
+void delete_item(int index)
+{
+ __sync_fetch_and_add(&epoll_items[index].deleted, 1);
+}
+
+/*
+ * A pointer to a read_thread_data structure will be passed as the argument to
+ * each read thread:
+ */
+struct read_thread_data {
+ int stop;
+ int status; /* Indicates any error encountered by the read thread. */
+ int epoll_set;
+};
+
+/*
+ * The function executed by the read threads:
+ */
+void *read_thread_function(void *function_data)
+{
+ struct read_thread_data *thread_data =
+ (struct read_thread_data *)function_data;
+ struct epoll_event event_data;
+ struct epoll_item_private *item_data;
+ char socket_data;
+
+ /* Handle events until we encounter an error or this thread's 'stop'
+ condition is set: */
+ while (1) {
+ int result = epoll_wait(thread_data->epoll_set,
+ &event_data,
+ 1, /* Number of desired events */
+ 1000); /* Timeout in ms */
+ if (result < 0) {
+ /* Breakpoints signal all threads. Ignore that while
+ debugging: */
+ if (errno == EINTR)
+ continue;
+ thread_data->status = errno;
+ return 0;
+ } else if (thread_data->stop)
+ return 0;
+ else if (result == 0) /* Timeout */
+ continue;
+
+ /* We need the mutex here because checking for the stop
+ condition and re-enabling the epoll item need to be done
+ together as one atomic operation when EPOLL_CTL_DISABLE is
+ available: */
+ item_data = (struct epoll_item_private *)event_data.data.ptr;
+ pthread_mutex_lock(&item_data->mutex);
+
+ /* Remove the item from the epoll set if we want to stop
+ handling that event: */
+ if (item_data->stop)
+ delete_item(item_data->index);
+ else {
+ /* Clear the data that was written to the other end of
+ our non-blocking socket: */
+ do {
+ if (read(item_data->fd, &socket_data, 1) < 1) {
+ if ((errno == EAGAIN) ||
+ (errno == EWOULDBLOCK))
+ break;
+ else
+ goto error_unlock;
+ }
+ } while (item_data->events & EPOLLET);
+
+ /* The item was one-shot, so re-enable it: */
+ event_data.events = item_data->events;
+ if (epoll_ctl(thread_data->epoll_set,
+ EPOLL_CTL_MOD,
+ item_data->fd,
+ &event_data) < 0)
+ goto error_unlock;
+ }
+
+ pthread_mutex_unlock(&item_data->mutex);
+ }
+
+error_unlock:
+ thread_data->status = item_data->status = errno;
+ pthread_mutex_unlock(&item_data->mutex);
+ return 0;
+}
+
+/*
+ * A pointer to a write_thread_data structure will be passed as the argument to
+ * the write thread:
+ */
+struct write_thread_data {
+ int stop;
+ int status; /* Indicates any error encountered by the write thread. */
+ int n_fds;
+ int *fds;
+};
+
+/*
+ * The function executed by the write thread. It writes a single byte to each
+ * socket in turn until the stop condition for this thread is set. If writing to
+ * a socket would block (i.e. errno was EAGAIN), we leave that socket alone for
+ * the moment and just move on to the next socket in the list. We don't care
+ * about the order in which we deliver events to the epoll set. In fact we don't
+ * care about the data we're writing to the pipes at all; we just want to
+ * trigger epoll events:
+ */
+void *write_thread_function(void *function_data)
+{
+ const char data = 'X';
+ int index;
+ struct write_thread_data *thread_data =
+ (struct write_thread_data *)function_data;
+ while (!write_thread_data->stop)
+ for (index = 0;
+ !thread_data->stop && (index < thread_data->n_fds);
+ ++index)
+ if ((write(thread_data->fds[index], &data, 1) < 1) &&
+ (errno != EAGAIN) &&
+ (errno != EWOULDBLOCK)) {
+ write_thread_data->status = errno;
+ return;
+ }
+}
+
+/*
+ * Arguments are currently ignored:
+ */
+int main(int argc, char **argv)
+{
+ const int n_read_threads = 100;
+ const int n_epoll_items = 500;
+ int index;
+ int epoll_set = epoll_create1(0);
+ struct write_thread_data write_thread_data = {
+ 0, 0, n_epoll_items, malloc(n_epoll_items * sizeof(int))
+ };
+ struct read_thread_data *read_thread_data =
+ malloc(n_read_threads * sizeof(struct read_thread_data));
+ pthread_t *read_threads = malloc(n_read_threads * sizeof(pthread_t));
+ pthread_t write_thread;
+
+ printf("-----------------\n");
+ printf("Runing test_epoll\n");
+ printf("-----------------\n");
+
+ epoll_items = malloc(n_epoll_items * sizeof(struct epoll_item_private));
+
+ if (epoll_set < 0 || epoll_items == 0 || write_thread_data.fds == 0 ||
+ read_thread_data == 0 || read_threads == 0)
+ goto error;
+
+ if (sysconf(_SC_NPROCESSORS_ONLN) < 2) {
+ printf("Error: please run this test on a multi-core system.\n");
+ goto error;
+ }
+
+ /* Create the socket pairs and epoll items: */
+ for (index = 0; index < n_epoll_items; ++index) {
+ int socket_pair[2];
+ struct epoll_event event_data;
+ if (socketpair(AF_UNIX,
+ SOCK_STREAM | SOCK_NONBLOCK,
+ 0,
+ socket_pair) < 0)
+ goto error;
+ write_thread_data.fds[index] = socket_pair[0];
+ epoll_items[index].index = index;
+ epoll_items[index].fd = socket_pair[1];
+ if (pthread_mutex_init(&epoll_items[index].mutex, NULL) != 0)
+ goto error;
+ /* We always use EPOLLONESHOT because this test is currently
+ structured to demonstrate the need for EPOLL_CTL_DISABLE,
+ which only produces useful information in the EPOLLONESHOT
+ case (without EPOLLONESHOT, calling epoll_ctl with
+ EPOLL_CTL_DISABLE will never return EBUSY). If support for
+ testing events without EPOLLONESHOT is desired, it should
+ probably be implemented in a separate unit test. */
+ epoll_items[index].events = EPOLLIN | EPOLLONESHOT;
+ if (index < n_epoll_items / 2)
+ epoll_items[index].events |= EPOLLET;
+ epoll_items[index].stop = 0;
+ epoll_items[index].status = 0;
+ epoll_items[index].deleted = 0;
+ event_data.events = epoll_items[index].events;
+ event_data.data.ptr = &epoll_items[index];
+ if (epoll_ctl(epoll_set,
+ EPOLL_CTL_ADD,
+ epoll_items[index].fd,
+ &event_data) < 0)
+ goto error;
+ }
+
+ /* Create and start the read threads: */
+ for (index = 0; index < n_read_threads; ++index) {
+ read_thread_data[index].stop = 0;
+ read_thread_data[index].status = 0;
+ read_thread_data[index].epoll_set = epoll_set;
+ if (pthread_create(&read_threads[index],
+ NULL,
+ read_thread_function,
+ &read_thread_data[index]) != 0)
+ goto error;
+ }
+
+ if (pthread_create(&write_thread,
+ NULL,
+ write_thread_function,
+ &write_thread_data) != 0)
+ goto error;
+
+ /* Cancel all event pollers: */
+#ifdef EPOLL_CTL_DISABLE
+ for (index = 0; index < n_epoll_items; ++index) {
+ pthread_mutex_lock(&epoll_items[index].mutex);
+ ++epoll_items[index].stop;
+ if (epoll_ctl(epoll_set,
+ EPOLL_CTL_DISABLE,
+ epoll_items[index].fd,
+ NULL) == 0)
+ delete_item(index);
+ else if (errno != EBUSY) {
+ pthread_mutex_unlock(&epoll_items[index].mutex);
+ goto error;
+ }
+ /* EBUSY means events were being handled; allow the other thread
+ to delete the item. */
+ pthread_mutex_unlock(&epoll_items[index].mutex);
+ }
+#else
+ for (index = 0; index < n_epoll_items; ++index) {
+ pthread_mutex_lock(&epoll_items[index].mutex);
+ ++epoll_items[index].stop;
+ pthread_mutex_unlock(&epoll_items[index].mutex);
+ /* Wait in case a thread running read_thread_function is
+ currently executing code between epoll_wait and
+ pthread_mutex_lock with this item. Note that a longer delay
+ would make double-deletion less likely (at the expense of
+ performance), but there is no guarantee that any delay would
+ ever be sufficient. Note also that we delete all event
+ pollers at once for testing purposes, but in a real-world
+ environment we are likely to want to be able to cancel event
+ pollers at arbitrary times. Therefore we can't improve this
+ situation by just splitting this loop into two loops
+ (i.e. signal 'stop' for all items, sleep, and then delete all
+ items). We also can't fix the problem via EPOLL_CTL_DEL
+ because that command can't prevent the case where some other
+ thread is executing read_thread_function within the region
+ mentioned above: */
+ usleep(1);
+ pthread_mutex_lock(&epoll_items[index].mutex);
+ if (!epoll_items[index].deleted)
+ delete_item(index);
+ pthread_mutex_unlock(&epoll_items[index].mutex);
+ }
+#endif
+
+ /* Shut down the read threads: */
+ for (index = 0; index < n_read_threads; ++index)
+ __sync_fetch_and_add(&read_thread_data[index].stop, 1);
+ for (index = 0; index < n_read_threads; ++index) {
+ if (pthread_join(read_threads[index], NULL) != 0)
+ goto error;
+ if (read_thread_data[index].status)
+ goto error;
+ }
+
+ /* Shut down the write thread: */
+ __sync_fetch_and_add(&write_thread_data.stop, 1);
+ if ((pthread_join(write_thread, NULL) != 0) || write_thread_data.status)
+ goto error;
+
+ /* Check for final error conditions: */
+ for (index = 0; index < n_epoll_items; ++index) {
+ if (epoll_items[index].status != 0)
+ goto error;
+ if (pthread_mutex_destroy(&epoll_items[index].mutex) < 0)
+ goto error;
+ }
+ for (index = 0; index < n_epoll_items; ++index)
+ if (epoll_items[index].deleted != 1) {
+ printf("Error: item data deleted %1d times.\n",
+ epoll_items[index].deleted);
+ goto error;
+ }
+
+ printf("[PASS]\n");
+ return 0;
+
+ error:
+ printf("[FAIL]\n");
+ return errno;
+}