#include <side/trace.h>
#include <string.h>
#include <assert.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <poll.h>
+#include "compiler.h"
#include "rcu.h"
#include "list.h"
#include "rculist.h"
/* Key 0x2 is reserved for ptrace. */
#define SIDE_KEY_PTRACE 0x2
+#define SIDE_RETRY_BUSY_LOOP_ATTEMPTS 100
+#define SIDE_RETRY_DELAY_MS 1
+
struct side_events_register_handle {
struct side_list_node node;
struct side_event_description **events;
uint64_t key;
};
+enum agent_thread_state {
+ AGENT_THREAD_STATE_BLOCKED = 0,
+ AGENT_THREAD_STATE_HANDLE_REQUEST = (1 << 0),
+ AGENT_THREAD_STATE_EXIT = (1 << 1),
+ AGENT_THREAD_STATE_PAUSE = (1 << 2),
+ AGENT_THREAD_STATE_PAUSE_ACK = (1 << 3),
+};
+
+struct statedump_agent_thread {
+ long ref;
+ pthread_t id;
+ enum agent_thread_state state;
+ pthread_cond_t worker_cond;
+ pthread_cond_t waiter_cond;
+};
+
static struct side_rcu_gp_state event_rcu_gp, statedump_rcu_gp;
/*
static pthread_mutex_t side_event_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
static pthread_mutex_t side_statedump_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
static pthread_mutex_t side_key_lock = PTHREAD_MUTEX_INITIALIZER;
+/*
+ * The side_agent_thread_lock protects the life-time of the agent
+ * thread: reference counting, creation, join. It is not taken by
+ * the agent thread per se so it does not have a circular dependency
+ * with pthread join.
+ * The side_statedump_lock nests inside the side_agent_thread_lock.
+ */
+static pthread_mutex_t side_agent_thread_lock = PTHREAD_MUTEX_INITIALIZER;
/* Dynamic tracer key allocation. */
static uint64_t side_key_next = SIDE_KEY_RESERVED_RANGE_END;
+static struct statedump_agent_thread statedump_agent_thread;
+
static DEFINE_SIDE_LIST_HEAD(side_events_list);
static DEFINE_SIDE_LIST_HEAD(side_tracer_list);
abort();
notif->key = key;
side_list_insert_node_tail(&handle->notification_queue, ¬if->node);
+ if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD) {
+ (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_HANDLE_REQUEST, __ATOMIC_SEQ_CST);
+ pthread_cond_broadcast(&statedump_agent_thread.worker_cond);
+ }
}
/* Called with side_statedump_lock held. */
}
}
+static
+void side_statedump_run(struct side_statedump_request_handle *handle,
+ struct side_statedump_notification *notif)
+{
+ /* Invoke the state dump callback specifically for the tracer key. */
+ filter_key = notif->key;
+ side_statedump_event_call(side_statedump_begin,
+ side_arg_list(side_arg_string(handle->name)));
+ handle->cb();
+ side_statedump_event_call(side_statedump_end,
+ side_arg_list(side_arg_string(handle->name)));
+ filter_key = SIDE_KEY_MATCH_ALL;
+}
+
+static
+void _side_statedump_run_pending_requests(struct side_statedump_request_handle *handle)
+{
+ struct side_statedump_notification *notif, *tmp;
+ DEFINE_SIDE_LIST_HEAD(tmp_head);
+
+ pthread_mutex_lock(&side_statedump_lock);
+ side_list_splice(&handle->notification_queue, &tmp_head);
+ side_list_head_init(&handle->notification_queue);
+ pthread_mutex_unlock(&side_statedump_lock);
+
+ /* We are now sole owner of the tmp_head list. */
+ side_list_for_each_entry(notif, &tmp_head, node)
+ side_statedump_run(handle, notif);
+ side_list_for_each_entry_safe(notif, tmp, &tmp_head, node)
+ free(notif);
+
+ if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD) {
+ pthread_mutex_lock(&side_statedump_lock);
+ pthread_cond_broadcast(&statedump_agent_thread.waiter_cond);
+ pthread_mutex_unlock(&side_statedump_lock);
+ }
+}
+
+static
+void *statedump_agent_func(void *arg __attribute__((unused)))
+{
+ for (;;) {
+ struct side_statedump_request_handle *handle;
+ struct side_rcu_read_state rcu_read_state;
+ enum agent_thread_state state;
+
+ pthread_mutex_lock(&side_statedump_lock);
+ for (;;) {
+ state = __atomic_load_n(&statedump_agent_thread.state, __ATOMIC_SEQ_CST);
+ if (state == AGENT_THREAD_STATE_BLOCKED)
+ pthread_cond_wait(&statedump_agent_thread.worker_cond, &side_statedump_lock);
+ else
+ break;
+ }
+ pthread_mutex_unlock(&side_statedump_lock);
+ if (state & AGENT_THREAD_STATE_EXIT)
+ break;
+ if (state & AGENT_THREAD_STATE_PAUSE) {
+ int attempt = 0;
+
+ (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_PAUSE_ACK, __ATOMIC_SEQ_CST);
+ for (;;) {
+ state = __atomic_load_n(&statedump_agent_thread.state, __ATOMIC_SEQ_CST);
+ if (!(state & AGENT_THREAD_STATE_PAUSE))
+ break;
+ if (attempt > SIDE_RETRY_BUSY_LOOP_ATTEMPTS) {
+ (void)poll(NULL, 0, SIDE_RETRY_DELAY_MS);
+ continue;
+ }
+ attempt++;
+ side_cpu_relax();
+ }
+ continue;
+ }
+ (void)__atomic_and_fetch(&statedump_agent_thread.state, ~AGENT_THREAD_STATE_HANDLE_REQUEST, __ATOMIC_SEQ_CST);
+ side_rcu_read_begin(&statedump_rcu_gp, &rcu_read_state);
+ side_list_for_each_entry_rcu(handle, &side_statedump_list, node)
+ _side_statedump_run_pending_requests(handle);
+ side_rcu_read_end(&statedump_rcu_gp, &rcu_read_state);
+ }
+ return NULL;
+}
+
+static
+void statedump_agent_thread_init(void)
+{
+ pthread_cond_init(&statedump_agent_thread.worker_cond, NULL);
+ pthread_cond_init(&statedump_agent_thread.waiter_cond, NULL);
+ statedump_agent_thread.state = AGENT_THREAD_STATE_BLOCKED;
+}
+
+/* Called with side_agent_thread_lock and side_statedump_lock held. */
+static
+void statedump_agent_thread_get(void)
+{
+ int ret;
+
+ if (statedump_agent_thread.ref++)
+ return;
+ statedump_agent_thread_init();
+ ret = pthread_create(&statedump_agent_thread.id, NULL,
+ statedump_agent_func, NULL);
+ if (ret) {
+ abort();
+ }
+}
+
+/*
+ * Called with side_agent_thread_lock and side_statedump_lock held.
+ * Returns true if join for agent thread is needed.
+ */
+static
+bool statedump_agent_thread_put(void)
+{
+ if (--statedump_agent_thread.ref)
+ return false;
+ (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_EXIT, __ATOMIC_SEQ_CST);
+ pthread_cond_broadcast(&statedump_agent_thread.worker_cond);
+ return true;
+}
+
+static
+void statedump_agent_thread_fini(void)
+{
+ statedump_agent_thread.state = AGENT_THREAD_STATE_BLOCKED;
+ if (pthread_cond_destroy(&statedump_agent_thread.worker_cond))
+ abort();
+ if (pthread_cond_destroy(&statedump_agent_thread.waiter_cond))
+ abort();
+}
+
+/* Called with side_agent_thread_lock held. */
+static
+void statedump_agent_thread_join(void)
+{
+ int ret;
+ void *retval;
+
+ ret = pthread_join(statedump_agent_thread.id, &retval);
+ if (ret) {
+ abort();
+ }
+ statedump_agent_thread_fini();
+}
+
struct side_statedump_request_handle *
side_statedump_request_notification_register(const char *state_name,
void (*statedump_cb)(void),
handle->mode = mode;
side_list_head_init(&handle->notification_queue);
+ if (mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
+ pthread_mutex_lock(&side_agent_thread_lock);
pthread_mutex_lock(&side_statedump_lock);
+ if (mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
+ statedump_agent_thread_get();
side_list_insert_node_tail_rcu(&side_statedump_list, &handle->node);
/* Queue statedump pending for all tracers. */
queue_statedump_pending(handle, SIDE_KEY_MATCH_ALL);
pthread_mutex_unlock(&side_statedump_lock);
+ if (mode == SIDE_STATEDUMP_MODE_AGENT_THREAD) {
+ pthread_mutex_unlock(&side_agent_thread_lock);
+
+ pthread_mutex_lock(&side_statedump_lock);
+ while (!side_list_empty(&handle->notification_queue))
+ pthread_cond_wait(&statedump_agent_thread.waiter_cond, &side_statedump_lock);
+ pthread_mutex_unlock(&side_statedump_lock);
+ }
+
return handle;
name_nomem:
void side_statedump_request_notification_unregister(struct side_statedump_request_handle *handle)
{
+ bool join = false;
+
if (finalized)
return;
if (!initialized)
side_init();
assert(!filter_key);
+ if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
+ pthread_mutex_lock(&side_agent_thread_lock);
pthread_mutex_lock(&side_statedump_lock);
unqueue_statedump_pending(handle, SIDE_KEY_MATCH_ALL);
side_list_remove_node_rcu(&handle->node);
+ if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
+ join = statedump_agent_thread_put();
pthread_mutex_unlock(&side_statedump_lock);
+ if (join)
+ statedump_agent_thread_join();
+ if (handle->mode == SIDE_STATEDUMP_MODE_AGENT_THREAD)
+ pthread_mutex_unlock(&side_agent_thread_lock);
side_rcu_wait_grace_period(&statedump_rcu_gp);
free(handle->name);
return ret;
}
-static
-void side_statedump_run(struct side_statedump_request_handle *handle,
- struct side_statedump_notification *notif)
-{
- /* Invoke the state dump callback specifically for the tracer key. */
- filter_key = notif->key;
- side_statedump_event_call(side_statedump_begin,
- side_arg_list(side_arg_string(handle->name)));
- handle->cb();
- side_statedump_event_call(side_statedump_end,
- side_arg_list(side_arg_string(handle->name)));
- filter_key = SIDE_KEY_MATCH_ALL;
-}
-
-static
-void _side_statedump_run_pending_requests(struct side_statedump_request_handle *handle)
-{
- struct side_statedump_notification *notif, *tmp;
- DEFINE_SIDE_LIST_HEAD(tmp_head);
-
- pthread_mutex_lock(&side_statedump_lock);
- side_list_splice(&handle->notification_queue, &tmp_head);
- pthread_mutex_lock(&side_statedump_lock);
-
- /* We are now sole owner of the tmp_head list. */
- side_list_for_each_entry(notif, &tmp_head, node)
- side_statedump_run(handle, notif);
- side_list_for_each_entry_safe(notif, tmp, &tmp_head, node)
- free(notif);
-}
-
/*
* Only polling mode state dump handles allow application to explicitly handle the
* pending requests.
return ret;
}
+/*
+ * Use of pthread_atfork depends on glibc 2.24 to eliminate hangs when
+ * waiting for the agent thread if the agent thread calls malloc. This
+ * is corrected by GNU libc
+ * commit 8a727af925be63aa6ea0f5f90e16751fd541626b.
+ * Ref. https://bugzilla.redhat.com/show_bug.cgi?id=906468
+ */
+static
+void side_before_fork(void)
+{
+ int attempt = 0;
+
+ pthread_mutex_lock(&side_agent_thread_lock);
+ if (!statedump_agent_thread.ref)
+ return;
+ /* Pause agent thread. */
+ pthread_mutex_lock(&side_statedump_lock);
+ (void)__atomic_or_fetch(&statedump_agent_thread.state, AGENT_THREAD_STATE_PAUSE, __ATOMIC_SEQ_CST);
+ pthread_cond_broadcast(&statedump_agent_thread.worker_cond);
+ pthread_mutex_unlock(&side_statedump_lock);
+ /* Wait for agent thread acknowledge. */
+ while (!(__atomic_load_n(&statedump_agent_thread.state, __ATOMIC_SEQ_CST) & AGENT_THREAD_STATE_PAUSE_ACK)) {
+ if (attempt > SIDE_RETRY_BUSY_LOOP_ATTEMPTS) {
+ (void)poll(NULL, 0, SIDE_RETRY_DELAY_MS);
+ continue;
+ }
+ attempt++;
+ side_cpu_relax();
+ }
+}
+
+static
+void side_after_fork_parent(void)
+{
+ if (statedump_agent_thread.ref)
+ (void)__atomic_and_fetch(&statedump_agent_thread.state,
+ ~(AGENT_THREAD_STATE_PAUSE | AGENT_THREAD_STATE_PAUSE_ACK),
+ __ATOMIC_SEQ_CST);
+ pthread_mutex_unlock(&side_agent_thread_lock);
+}
+
+/*
+ * The agent thread does not exist in the child process after a fork.
+ * Re-initialize its data structures and create a new agent thread.
+ */
+static
+void side_after_fork_child(void)
+{
+ if (statedump_agent_thread.ref) {
+ int ret;
+
+ statedump_agent_thread_fini();
+ statedump_agent_thread_init();
+ ret = pthread_create(&statedump_agent_thread.id, NULL,
+ statedump_agent_func, NULL);
+ if (ret) {
+ abort();
+ }
+ }
+ pthread_mutex_unlock(&side_agent_thread_lock);
+}
+
void side_init(void)
{
if (initialized)
return;
side_rcu_gp_init(&event_rcu_gp);
side_rcu_gp_init(&statedump_rcu_gp);
+ if (pthread_atfork(side_before_fork, side_after_fork_parent, side_after_fork_child))
+ abort();
initialized = true;
}
projects / libside.git / blobdiff