Merge pull request #594 from mihalicyn/fuse_interrupt

Partial support for FUSE_INTERRUPT

src/bindings.c

@@ -149,6 +149,25 @@ static inline void store_unlock(void)
 	mutex_unlock(&pidns_store_mutex);
 }
 
+#define define_interruptible_lock(type, lockname, lockfn)           \
+        int lockname##_interruptible(type *l)                       \
+        {                                                           \
+                int ret = ETIMEDOUT;                                \
+                while (!fuse_interrupted() && (ret == ETIMEDOUT)) { \
+                        struct timespec deadline;                   \
+                        clock_gettime(CLOCK_REALTIME, &deadline);   \
+                        deadline.tv_sec += 1;                       \
+                        ret = lockfn(l, &deadline);                 \
+                }                                                   \
+                return -ret;                                        \
+        }
+
+define_interruptible_lock(pthread_mutex_t, mutex_lock, pthread_mutex_timedlock)
+define_interruptible_lock(pthread_rwlock_t, rwlock_rdlock, pthread_rwlock_timedrdlock)
+define_interruptible_lock(pthread_rwlock_t, rwlock_wrlock, pthread_rwlock_timedwrlock)
+
+#undef define_interruptible_lock
+
 /* /proc/       =    6
  *                +
  * <pid-as-str> =   INTTYPE_TO_STRLEN(pid_t)

src/bindings.h

@@ -78,6 +78,24 @@ enum lxcfs_virt_t {
 #define LXCFS_TYPE_SYS(type) (type >= LXC_TYPE_SYS && type <= LXC_TYPE_SYS_DEVICES_SYSTEM_CPU_ONLINE)
 #define LXCFS_TYPE_OK(type) (type >= LXC_TYPE_CGDIR && type < LXC_TYPE_MAX)
 
+/*
+ * This signal will be used to signal fuse request processing thread that
+ * request was interrupted (FUSE_INTERRUPT came from the kernel).
+ *
+ * It's not imporant which signal num is used, but it should not intersect with
+ * any signals those are already handled and used somewhere.
+ * Since, SIGUSR1 and SIGUSR2 are already utilized by lxcfs, let it be SIGTTOU.
+ *
+ * See also:
+ * ("interrupt support")
+ * https://github.com/libfuse/libfuse/commit/288ed4ebcea335c77793ee3d207c7466d55c4f71
+ */
+#define LXCFS_INTR_SIGNAL SIGTTOU
+
+extern int mutex_lock_interruptible(pthread_mutex_t *l);
+extern int rwlock_rdlock_interruptible(pthread_rwlock_t *l);
+extern int rwlock_wrlock_interruptible(pthread_rwlock_t *l);
+
 struct file_info {
 	char *controller;
 	char *cgroup;

src/lxcfs.c

@@ -1051,6 +1051,42 @@ int lxcfs_chmod(const char *path, mode_t mode)
 	return -ENOENT;
 }
 
+#if HAVE_FUSE3
+static void fuse_intr_sighandler(int sig)
+{
+	(void) sig;
+	/* Nothing to do */
+}
+
+static int fuse_init_intr_signal(int signum)
+{
+	struct sigaction old_sa;
+	struct sigaction sa;
+
+	if (sigaction(signum, NULL, &old_sa) == -1)
+		return log_error(-1, "cannot get old signal handler\n");
+
+	if (old_sa.sa_handler != SIG_DFL)
+		return log_error(-1, "%d has non-default handler\n", signum);
+
+	memset(&sa, 0, sizeof(struct sigaction));
+
+	/*
+	 * We *must* enable SA_RESTART, otherwise we may accidentally
+	 * break some code which is not ready to signals/fuse interrupt.
+	 */
+	sa.sa_flags = SA_RESTART;
+
+	sa.sa_handler = fuse_intr_sighandler;
+	sigemptyset(&sa.sa_mask);
+
+	if (sigaction(signum, &sa, NULL) == -1)
+		return log_error(-1, "cannot set interrupt signal handler\n");
+
+	return 0;
+}
+#endif
+
 #if HAVE_FUSE3
 static void *lxcfs_init(struct fuse_conn_info *conn, struct fuse_config *cfg)
 #else
@@ -1062,6 +1098,8 @@ static void *lxcfs_init(struct fuse_conn_info *conn)
 
 #if HAVE_FUSE3
 	cfg->direct_io = 1;
+	cfg->intr = 1;
+	cfg->intr_signal = LXCFS_INTR_SIGNAL;
 #endif
 
 	return fuse_get_context()->private_data;
@@ -1402,6 +1440,13 @@ int main(int argc, char *argv[])
 		goto out;
 	}
 
+#if HAVE_FUSE3
+	if (fuse_init_intr_signal(LXCFS_INTR_SIGNAL)) {
+		lxcfs_error("Failed to install fuse interrupt signal handler");
+		goto out;
+	}
+#endif
+
 	if (!pidfile) {
 		snprintf(pidfile_buf, sizeof(pidfile_buf), "%s/lxcfs.pid", RUNTIME_PATH);
 		pidfile = pidfile_buf;

src/proc_cpuview.c

@@ -286,7 +286,8 @@ static void prune_proc_stat_history(void)
 	time_t now = time(NULL);
 
 	for (int i = 0; i < CPUVIEW_HASH_SIZE; i++) {
-		pthread_rwlock_wrlock(&proc_stat_history[i]->lock);
+		if (rwlock_wrlock_interruptible(&proc_stat_history[i]->lock))
+			continue;
 
 		if ((proc_stat_history[i]->lastcheck + PROC_STAT_PRUNE_INTERVAL) > now) {
 			pthread_rwlock_unlock(&proc_stat_history[i]->lock);
@@ -308,7 +309,8 @@ static struct cg_proc_stat *find_proc_stat_node(struct cg_proc_stat_head *head,
 	struct cg_proc_stat *node;
 
 	prune_proc_stat_history();
-	pthread_rwlock_rdlock(&head->lock);
+	if (rwlock_rdlock_interruptible(&head->lock))
+		return NULL;
 
 	if (!head->next) {
 		pthread_rwlock_unlock(&head->lock);
@@ -319,7 +321,13 @@ static struct cg_proc_stat *find_proc_stat_node(struct cg_proc_stat_head *head,
 
 	do {
 		if (strcmp(cg, node->cg) == 0) {
-			pthread_mutex_lock(&node->lock);
+			/*
+			 * If we are failed to take a lock OR
+			 * fuse request was interrupted then
+			 * just return NULL and exit gracefully.
+			 */
+			if (mutex_lock_interruptible(&node->lock))
+				node = NULL;
 			goto out;
 		}
 	} while ((node = node->next));
@@ -340,6 +348,10 @@ static struct cg_proc_stat *find_or_create_proc_stat_node(struct cpuacct_usage *
 
 	node = find_proc_stat_node(head, cg);
 	if (!node) {
+		/* safe place to exit */
+		if (fuse_interrupted())
+			return NULL;
+
 		node = new_proc_stat_node(usage, cpu_count, cg);
 		if (!node)
 			return NULL;