Re: Revisiting threaded udevd

[Scott James Remnant <scott@canonical.com>]

[-- Attachment #1.1: Type: text/plain, Size: 615 bytes --]

On Mon, 2008-12-22 at 11:25 +0000, Alan Jenkins wrote:

> I have some time to look at this again now.
> 
I was just looking at this myself, since it formed a natural part of the
performance testing I'm doing on Ubuntu.

I got as far as reapplying the patches to current git head, but then hit
a segfault :-(

Attached is the patch against head.

The segfault occurs in the udev_device_get_properties() call at the top
of udev_exec(), because that calls update_envp_monitor_buf() which calls
free().

I assume this is non-reentrant territory?

Scott
-- 
Scott James Remnant
scott@canonical.com

[-- Attachment #1.2: threaded.patch --]
[-- Type: text/x-patch, Size: 23778 bytes --]

=== modified file 'configure.ac'
--- configure.ac	2008-12-16 15:17:53 +0000
+++ configure.ac	2008-12-24 11:16:17 +0000
@@ -9,6 +9,8 @@
 AC_SYS_LARGEFILE
 AC_PROG_LIBTOOL
 
+sinclude(acx_pthread.m4)
+
 dnl /* libudev version */
 LIBUDEV_LT_CURRENT=0
 LIBUDEV_LT_REVISION=6
@@ -25,6 +27,8 @@
 AC_SUBST(VOLID_LT_REVISION)
 AC_SUBST(VOLID_LT_AGE)
 
+ACX_PTHREAD(AC_DEFINE(HAVE_PTHREAD), AC_MSG_FAILURE([pthreads unavailable]))
+
 AC_PATH_PROG([XSLTPROC], [xsltproc])
 
 AC_CHECK_LIB(c, inotify_init,

=== modified file 'udev/Makefile.am'
--- udev/Makefile.am	2008-12-06 03:03:08 +0000
+++ udev/Makefile.am	2008-12-24 11:16:17 +0000
@@ -1,5 +1,9 @@
 include $(top_srcdir)/Makefile.am.inc
 
+LIBS += $(PTHREAD_LIBS)
+CFLAGS += $(PTHREAD_CFLAGS)
+CC=$(PTHREAD_CC)
+
 SUBDIRS = \
 	lib
 
@@ -18,6 +22,7 @@
 	udev-event.c \
 	udev-node.c \
 	udev-rules.c \
+	udev-exec.c \
 	udev-util.c \
 	lib/libudev.h \
 	lib/libudev-private.h \

=== modified file 'udev/test-udev.c'
--- udev/test-udev.c	2008-10-24 08:51:04 +0000
+++ udev/test-udev.c	2008-12-24 11:16:28 +0000
@@ -60,6 +60,9 @@
 	info(udev, "version %s\n", VERSION);
 	udev_selinux_init(udev);
 
+	/* fork exec daemon before opening fds or changing signal handling */
+	udev_exec_init(udev);
+
 	/* set signal handlers */
 	memset(&act, 0x00, sizeof(act));
 	act.sa_handler = (void (*)(int)) sig_handler;
@@ -69,9 +72,6 @@
 	sigaction(SIGINT, &act, NULL);
 	sigaction(SIGTERM, &act, NULL);
 
-	/* trigger timeout to prevent hanging processes */
-	alarm(UDEV_EVENT_TIMEOUT);
-
 	action = getenv("ACTION");
 	devpath = getenv("DEVPATH");
 	subsystem = getenv("SUBSYSTEM");
@@ -99,10 +99,6 @@
 	event = udev_event_new(dev);
 	err = udev_event_execute_rules(event, rules);
 
-	/* rules may change/disable the timeout */
-	if (udev_device_get_event_timeout(dev) >= 0)
-		alarm(udev_device_get_event_timeout(dev));
-
 	if (err == 0 && !event->ignore_device && udev_get_run(udev))
 		udev_event_execute_run(event);
 
@@ -111,6 +107,7 @@
 fail:
 	udev_rules_unref(rules);
 exit:
+	udev_exec_cleanup(udev);
 	udev_selinux_exit(udev);
 	udev_unref(udev);
 	if (err != 0)

=== modified file 'udev/udev-event.c'
--- udev/udev-event.c	2008-12-02 00:04:23 +0000
+++ udev/udev-event.c	2008-12-24 11:10:39 +0000
@@ -717,7 +717,7 @@
 				       udev_device_get_seqnum(event->dev),
 				       program);
 			envp = udev_device_get_properties_envp(event->dev);
-			if (util_run_program(event->udev, program, envp, NULL, 0, NULL) != 0) {
+			if (udev_exec(event->dev, program, NULL, 0, NULL) != 0) {
 				if (!udev_list_entry_get_flag(list_entry))
 					err = -1;
 			}

=== modified file 'udev/udev-rules.c'
--- udev/udev-rules.c	2008-11-24 20:24:04 +0000
+++ udev/udev-rules.c	2008-12-24 11:16:01 +0000
@@ -731,13 +731,11 @@
 static int import_program_into_properties(struct udev_device *dev, const char *program)
 {
 	struct udev *udev = udev_device_get_udev(dev);
-	char **envp;
 	char result[2048];
 	size_t reslen;
 	char *line;
 
-	envp = udev_device_get_properties_envp(dev);
-	if (util_run_program(udev, program, envp, result, sizeof(result), &reslen) != 0)
+	if (udev_exec(dev, program, result, sizeof(result), &reslen) != 0)
 		return -1;
 
 	line = result;
@@ -2190,19 +2188,17 @@
 		case TK_M_PROGRAM:
 			{
 				char program[UTIL_PATH_SIZE];
-				char **envp;
 				char result[UTIL_PATH_SIZE];
 
 				free(event->program_result);
 				event->program_result = NULL;
 				util_strlcpy(program, &rules->buf[cur->key.value_off], sizeof(program));
 				udev_event_apply_format(event, program, sizeof(program));
-				envp = udev_device_get_properties_envp(event->dev);
 				info(event->udev, "PROGRAM '%s' %s:%u\n",
 				     program,
 				     &rules->buf[rule->rule.filename_off],
 				     rule->rule.filename_line);
-				if (util_run_program(event->udev, program, envp, result, sizeof(result), NULL) != 0) {
+				if (udev_exec(event->udev, program, result, sizeof(result), NULL) != 0) {
 					if (cur->key.op != OP_NOMATCH)
 						goto nomatch;
 				} else {

=== modified file 'udev/udev-util.c'
--- udev/udev-util.c	2008-12-19 23:03:53 +0000
+++ udev/udev-util.c	2008-12-24 11:12:52 +0000
@@ -25,7 +25,6 @@
 #include <ctype.h>
 #include <pwd.h>
 #include <grp.h>
-#include <sys/wait.h>
 
 #include "udev.h"
 
@@ -238,215 +237,3 @@
 	udev_device_unref(dev);
 	return 0;
 }
-
-int util_run_program(struct udev *udev, const char *command, char **envp,
-		     char *result, size_t ressize, size_t *reslen)
-{
-	int status;
-	int outpipe[2] = {-1, -1};
-	int errpipe[2] = {-1, -1};
-	pid_t pid;
-	char arg[UTIL_PATH_SIZE];
-	char program[UTIL_PATH_SIZE];
-	char *argv[(sizeof(arg) / 2) + 1];
-	int devnull;
-	int i;
-	int err = 0;
-
-	/* build argv from command */
-	util_strlcpy(arg, command, sizeof(arg));
-	i = 0;
-	if (strchr(arg, ' ') != NULL) {
-		char *pos = arg;
-
-		while (pos != NULL && pos[0] != '\0') {
-			if (pos[0] == '\'') {
-				/* do not separate quotes */
-				pos++;
-				argv[i] = strsep(&pos, "\'");
-				while (pos != NULL && pos[0] == ' ')
-					pos++;
-			} else {
-				argv[i] = strsep(&pos, " ");
-			}
-			dbg(udev, "arg[%i] '%s'\n", i, argv[i]);
-			i++;
-		}
-		argv[i] = NULL;
-	} else {
-		argv[0] = arg;
-		argv[1] = NULL;
-	}
-	info(udev, "'%s'\n", command);
-
-	/* prepare pipes from child to parent */
-	if (result != NULL || udev_get_log_priority(udev) >= LOG_INFO) {
-		if (pipe(outpipe) != 0) {
-			err(udev, "pipe failed: %m\n");
-			return -1;
-		}
-	}
-	if (udev_get_log_priority(udev) >= LOG_INFO) {
-		if (pipe(errpipe) != 0) {
-			err(udev, "pipe failed: %m\n");
-			return -1;
-		}
-	}
-
-	/* allow programs in /lib/udev/ to be called without the path */
-	if (strchr(argv[0], '/') == NULL) {
-		util_strlcpy(program, UDEV_PREFIX "/lib/udev/", sizeof(program));
-		util_strlcat(program, argv[0], sizeof(program));
-		argv[0] = program;
-	}
-
-	pid = fork();
-	switch(pid) {
-	case 0:
-		/* child closes parent ends of pipes */
-		if (outpipe[READ_END] > 0)
-			close(outpipe[READ_END]);
-		if (errpipe[READ_END] > 0)
-			close(errpipe[READ_END]);
-
-		/* discard child output or connect to pipe */
-		devnull = open("/dev/null", O_RDWR);
-		if (devnull > 0) {
-			dup2(devnull, STDIN_FILENO);
-			if (outpipe[WRITE_END] < 0)
-				dup2(devnull, STDOUT_FILENO);
-			if (errpipe[WRITE_END] < 0)
-				dup2(devnull, STDERR_FILENO);
-			close(devnull);
-		} else
-			err(udev, "open /dev/null failed: %m\n");
-		if (outpipe[WRITE_END] > 0) {
-			dup2(outpipe[WRITE_END], STDOUT_FILENO);
-			close(outpipe[WRITE_END]);
-		}
-		if (errpipe[WRITE_END] > 0) {
-			dup2(errpipe[WRITE_END], STDERR_FILENO);
-			close(errpipe[WRITE_END]);
-		}
-		execve(argv[0], argv, envp);
-		if (errno == ENOENT || errno == ENOTDIR) {
-			/* may be on a filesytem which is not mounted right now */
-			info(udev, "program '%s' not found\n", argv[0]);
-		} else {
-			/* other problems */
-			err(udev, "exec of program '%s' failed\n", argv[0]);
-		}
-		_exit(1);
-	case -1:
-		err(udev, "fork of '%s' failed: %m\n", argv[0]);
-		return -1;
-	default:
-		/* read from child if requested */
-		if (outpipe[READ_END] > 0 || errpipe[READ_END] > 0) {
-			ssize_t count;
-			size_t respos = 0;
-
-			/* parent closes child ends of pipes */
-			if (outpipe[WRITE_END] > 0)
-				close(outpipe[WRITE_END]);
-			if (errpipe[WRITE_END] > 0)
-				close(errpipe[WRITE_END]);
-
-			/* read child output */
-			while (outpipe[READ_END] > 0 || errpipe[READ_END] > 0) {
-				int fdcount;
-				fd_set readfds;
-
-				FD_ZERO(&readfds);
-				if (outpipe[READ_END] > 0)
-					FD_SET(outpipe[READ_END], &readfds);
-				if (errpipe[READ_END] > 0)
-					FD_SET(errpipe[READ_END], &readfds);
-				fdcount = select(UDEV_MAX(outpipe[READ_END], errpipe[READ_END])+1, &readfds, NULL, NULL, NULL);
-				if (fdcount < 0) {
-					if (errno == EINTR)
-						continue;
-					err = -1;
-					break;
-				}
-
-				/* get stdout */
-				if (outpipe[READ_END] > 0 && FD_ISSET(outpipe[READ_END], &readfds)) {
-					char inbuf[1024];
-					char *pos;
-					char *line;
-
-					count = read(outpipe[READ_END], inbuf, sizeof(inbuf)-1);
-					if (count <= 0) {
-						close(outpipe[READ_END]);
-						outpipe[READ_END] = -1;
-						if (count < 0) {
-							err(udev, "stdin read failed: %m\n");
-							err = -1;
-						}
-						continue;
-					}
-					inbuf[count] = '\0';
-
-					/* store result for rule processing */
-					if (result) {
-						if (respos + count < ressize) {
-							memcpy(&result[respos], inbuf, count);
-							respos += count;
-						} else {
-							err(udev, "ressize %ld too short\n", (long)ressize);
-							err = -1;
-						}
-					}
-					pos = inbuf;
-					while ((line = strsep(&pos, "\n")))
-						if (pos || line[0] != '\0')
-							info(udev, "'%s' (stdout) '%s'\n", argv[0], line);
-				}
-
-				/* get stderr */
-				if (errpipe[READ_END] > 0 && FD_ISSET(errpipe[READ_END], &readfds)) {
-					char errbuf[1024];
-					char *pos;
-					char *line;
-
-					count = read(errpipe[READ_END], errbuf, sizeof(errbuf)-1);
-					if (count <= 0) {
-						close(errpipe[READ_END]);
-						errpipe[READ_END] = -1;
-						if (count < 0)
-							err(udev, "stderr read failed: %m\n");
-						continue;
-					}
-					errbuf[count] = '\0';
-					pos = errbuf;
-					while ((line = strsep(&pos, "\n")))
-						if (pos || line[0] != '\0')
-							info(udev, "'%s' (stderr) '%s'\n", argv[0], line);
-				}
-			}
-			if (outpipe[READ_END] > 0)
-				close(outpipe[READ_END]);
-			if (errpipe[READ_END] > 0)
-				close(errpipe[READ_END]);
-
-			/* return the childs stdout string */
-			if (result) {
-				result[respos] = '\0';
-				dbg(udev, "result='%s'\n", result);
-				if (reslen)
-					*reslen = respos;
-			}
-		}
-		waitpid(pid, &status, 0);
-		if (WIFEXITED(status)) {
-			info(udev, "'%s' returned with status %i\n", argv[0], WEXITSTATUS(status));
-			if (WEXITSTATUS(status) != 0)
-				err = -1;
-		} else {
-			err(udev, "'%s' abnormal exit\n", command);
-			err = -1;
-		}
-	}
-	return err;
-}

=== modified file 'udev/udev.h'
--- udev/udev.h	2008-11-05 20:49:52 +0000
+++ udev/udev.h	2008-12-24 11:16:47 +0000
@@ -35,6 +35,9 @@
 #define READ_END				0
 #define WRITE_END				1
 
+#define UDEVD_PRIORITY			-4 /* nice level for daemon */
+#define UDEV_PRIORITY			-2 /* nice level for programs run by daemon*/
+
 static inline void logging_init(const char *program_name)
 {
 	openlog(program_name, LOG_PID | LOG_CONS, LOG_DAEMON);
@@ -64,7 +67,7 @@
 	uid_t uid;
 	gid_t gid;
 	struct udev_list_node run_list;
-	pid_t pid;
+	pthread_t thread;
 	int exitstatus;
 	time_t queue_time;
 	unsigned long long int delaying_seqnum;
@@ -100,14 +103,18 @@
 extern int udev_node_remove(struct udev_device *dev, int test);
 extern void udev_node_update_old_links(struct udev_device *dev, struct udev_device *dev_old, int test);
 
+/* udev-exec.c */
+extern int udev_exec_init(struct udev *udev);
+extern void udev_exec_cleanup(struct udev *udev);
+extern int udev_exec(struct udev_device *dev, const char *command,
+                     char *result, size_t ressize, size_t *reslen);
+
 /* udev-util.c */
 extern int util_create_path(struct udev *udev, const char *path);
 extern int util_delete_path(struct udev *udev, const char *path);
 extern int util_unlink_secure(struct udev *udev, const char *filename);
 extern uid_t util_lookup_user(struct udev *udev, const char *user);
 extern gid_t util_lookup_group(struct udev *udev, const char *group);
-extern int util_run_program(struct udev *udev, const char *command, char **envp,
-			    char *result, size_t ressize, size_t *reslen);
 extern int util_resolve_subsys_kernel(struct udev *udev, const char *string,
 				      char *result, size_t maxsize, int read_value);
 

=== modified file 'udev/udevd.c'
--- udev/udevd.c	2008-11-17 13:43:58 +0000
+++ udev/udevd.c	2008-12-24 11:28:17 +0000
@@ -35,12 +35,10 @@
 #ifdef HAVE_INOTIFY
 #include <sys/inotify.h>
 #endif
+#include <pthread.h>
 
 #include "udev.h"
 
-#define UDEVD_PRIORITY			-4
-#define UDEV_PRIORITY			-2
-
 /* maximum limit of forked childs */
 #define UDEVD_MAX_CHILDS		256
 
@@ -64,7 +62,7 @@
 static struct udev_monitor *kernel_monitor;
 static int inotify_fd = -1;
 static int signal_pipe[2] = {-1, -1};
-static volatile int sigchilds_waiting;
+static int event_done_pipe[2] = {-1, -1};
 static volatile int udev_exit;
 static volatile int reload_config;
 static int run_exec_q;
@@ -73,6 +71,8 @@
 static int childs;
 static struct udev_list_node event_list;
 
+pthread_attr_t thread_attr;
+
 enum event_state {
 	EVENT_QUEUED,
 	EVENT_FINISHED,
@@ -167,87 +167,68 @@
 	udev_event_unref(event);
 }
 
-static void asmlinkage event_sig_handler(int signum)
-{
-	if (signum == SIGALRM)
-		exit(1);
-}
-
-static void event_fork(struct udev_event *event)
-{
-	pid_t pid;
-	struct sigaction act;
-	int err;
-
-	if (debug_trace) {
-		event->trace = 1;
-		fprintf(stderr, "fork %s (%llu)\n",
-		       udev_device_get_syspath(event->dev),
-		       udev_device_get_seqnum(event->dev));
-	}
-
-	pid = fork();
-	switch (pid) {
-	case 0:
-		/* child */
-		udev_monitor_unref(kernel_monitor);
-		udev_ctrl_unref(udev_ctrl);
-		if (inotify_fd >= 0)
-			close(inotify_fd);
-		close(signal_pipe[READ_END]);
-		close(signal_pipe[WRITE_END]);
-		logging_close();
-		logging_init("udevd-event");
-		setpriority(PRIO_PROCESS, 0, UDEV_PRIORITY);
-
-		/* set signal handlers */
-		memset(&act, 0x00, sizeof(act));
-		act.sa_handler = (void (*)(int)) event_sig_handler;
-		sigemptyset (&act.sa_mask);
-		act.sa_flags = 0;
-		sigaction(SIGALRM, &act, NULL);
-
-		/* reset to default */
-		act.sa_handler = SIG_DFL;
-		sigaction(SIGINT, &act, NULL);
-		sigaction(SIGTERM, &act, NULL);
-		sigaction(SIGCHLD, &act, NULL);
-		sigaction(SIGHUP, &act, NULL);
-
-		/* set timeout to prevent hanging processes */
-		alarm(UDEV_EVENT_TIMEOUT);
-
-		/* apply rules, create node, symlinks */
-		err = udev_event_execute_rules(event, rules);
-
-		/* rules may change/disable the timeout */
-		if (udev_device_get_event_timeout(event->dev) >= 0)
-			alarm(udev_device_get_event_timeout(event->dev));
-
-		/* execute RUN= */
-		if (err == 0 && !event->ignore_device && udev_get_run(event->udev))
-			udev_event_execute_run(event);
-
-		info(event->udev, "seq %llu exit with %i\n", udev_device_get_seqnum(event->dev), err);
-		logging_close();
-		if (err != 0)
-			exit(1);
-		exit(0);
-	case -1:
-		err(event->udev, "fork of child failed: %m\n");
+static int event_run(struct udev_event *event)
+{
+	int err;
+
+	/* apply rules, create node, symlinks */
+	err = udev_event_execute_rules(event, rules);
+
+	/* execute RUN= */
+	if (err == 0 && !event->ignore_device && udev_get_run(event->udev))
+		udev_event_execute_run(event);
+	info(event->udev, "seq %llu exit with %i\n", udev_device_get_seqnum(event->dev), err);
+
+	return err;
+}
+
+static void *event_run_pthread(void *arg)
+{
+	struct udev_event *event = arg;
+	int err;
+
+	err = event_run(event);
+
+	/* write to pipe, which will wakeup select() in our mainloop */
+	write(event_done_pipe[WRITE_END], &event, sizeof(struct udev_event *));
+
+	return (void *) (uintptr_t) err;
+}
+
+static void event_thread_create(struct udev_event *event)
+{
+	if (pthread_create(&event->thread, &thread_attr, event_run_pthread, event) != 0) {
+		err(event->udev, "create thread failed: %m\n");
 		event_queue_delete(event);
-		break;
-	default:
-		/* get SIGCHLD in main loop */
-		info(event->udev, "seq %llu forked, pid [%d], '%s' '%s', %ld seconds old\n",
-		     udev_device_get_seqnum(event->dev),
-		     pid,
-		     udev_device_get_action(event->dev),
-		     udev_device_get_subsystem(event->dev),
-		     time(NULL) - event->queue_time);
-		event->pid = pid;
-		childs++;
-	}
+	}
+
+	info(event->udev, "seq %llu created, '%s' '%s', %ld seconds old\n",
+	     udev_device_get_seqnum(event->dev),
+	     udev_device_get_action(event->dev),
+	     udev_device_get_subsystem(event->dev),
+	     time(NULL) - event->queue_time);
+}
+
+static int event_thread_join(struct udev_event *event)
+{
+	void *result;
+	int err;
+
+	err = pthread_join(event->thread, &result);
+	if (err) {
+		err(event->udev, "failed to retrieve thread return value: %m\n");
+		return -1;
+	}
+
+	return (int) (uintptr_t) result;
+}
+
+static void event_thread_kill(struct udev_event *event)
+{
+	pthread_kill(event->thread, SIGTERM);
+
+	/* Make sure thread has died before we return */
+	event_thread_join(event);
 }
 
 static void event_queue_insert(struct udev_event *event)
@@ -279,7 +260,7 @@
 
 	/* run all events with a timeout set immediately */
 	if (udev_device_get_timeout(event->dev) > 0) {
-		event_fork(event);
+		event_thread_create(event);
 		return;
 	}
 }
@@ -420,7 +401,7 @@
 			break;
 		}
 
-		if (loop_event->pid != 0)
+		if (loop_event->thread)
 			continue;
 
 		/* do not start event if parent or child event is still running */
@@ -431,7 +412,7 @@
 			continue;
 		}
 
-		event_fork(loop_event);
+		event_thread_create(loop_event);
 		dbg(udev, "moved seq %llu to running list\n", udev_device_get_seqnum(loop_event->dev));
 	}
 }
@@ -509,12 +490,9 @@
 	switch (signum) {
 		case SIGINT:
 		case SIGTERM:
+		case SIGCHLD:
 			udev_exit = 1;
 			break;
-		case SIGCHLD:
-			/* set flag, then write to pipe if needed */
-			sigchilds_waiting = 1;
-			break;
 		case SIGHUP:
 			reload_config = 1;
 			break;
@@ -524,50 +502,17 @@
 	write(signal_pipe[WRITE_END], "", 1);
 }
 
-static void udev_done(int pid, int exitstatus)
-{
-	struct udev_list_node *loop;
-
-	/* find event associated with pid and delete it */
-	udev_list_node_foreach(loop, &event_list) {
-		struct udev_event *loop_event = node_to_event(loop);
-
-		if (loop_event->pid == pid) {
-			info(loop_event->udev, "seq %llu cleanup, pid [%d], status %i, %ld seconds old\n",
-			     udev_device_get_seqnum(loop_event->dev), loop_event->pid,
-			     exitstatus, time(NULL) - loop_event->queue_time);
-			loop_event->exitstatus = exitstatus;
-			if (debug_trace)
-				fprintf(stderr, "exit %s (%llu)\n",
-				       udev_device_get_syspath(loop_event->dev),
-				       udev_device_get_seqnum(loop_event->dev));
-			event_queue_delete(loop_event);
-			childs--;
-
-			/* there may be dependent events waiting */
-			run_exec_q = 1;
-			return;
-		}
-	}
-}
-
-static void reap_sigchilds(void)
-{
-	pid_t pid;
-	int status;
-
-	while (1) {
-		pid = waitpid(-1, &status, WNOHANG);
-		if (pid <= 0)
-			break;
-		if (WIFEXITED(status))
-			status = WEXITSTATUS(status);
-		else if (WIFSIGNALED(status))
-			status = WTERMSIG(status) + 128;
-		else
-			status = 0;
-		udev_done(pid, status);
-	}
+static void udev_done(struct udev_event *event)
+{
+	event->exitstatus = event_thread_join(event);
+	info(event->udev, "seq %llu cleanup, status %i, %ld seconds old\n",
+	     udev_device_get_seqnum(event->dev),
+	     event->exitstatus, time(NULL) - event->queue_time);
+
+	event_queue_delete(event);
+
+	/* there may be events waiting with the same devpath */
+	run_exec_q = 1;
 }
 
 static void cleanup_queue_dir(struct udev *udev)
@@ -636,6 +581,8 @@
 	int err;
 	int fd;
 	struct sigaction act;
+	int pagesize;
+	int stacksize;
 	fd_set readfds;
 	const char *value;
 	int daemonize = 0;
@@ -706,6 +653,13 @@
 	if (write(STDERR_FILENO, 0, 0) < 0)
 		dup2(fd, STDERR_FILENO);
 
+	chdir("/");
+	umask(022);
+	setsid();
+
+	/* fork exec daemon before opening more fds or changing signal handling */
+	udev_exec_init(udev);
+
 	/* init control socket, bind() ensures, that only one udevd instance is running */
 	udev_ctrl = udev_ctrl_new_from_socket(udev, UDEV_CTRL_SOCK_PATH);
 	if (udev_ctrl == NULL) {
@@ -736,6 +690,11 @@
 		err(udev, "error getting pipes: %m\n");
 		goto exit;
 	}
+	err = pipe(event_done_pipe);
+	if (err < 0) {
+		err(udev, "error getting pipes: %m\n");
+		goto exit;
+	}
 
 	err = fcntl(signal_pipe[READ_END], F_GETFL, 0);
 	if (err < 0) {
@@ -799,9 +758,28 @@
 	/* set scheduling priority for the daemon */
 	setpriority(PRIO_PROCESS, 0, UDEVD_PRIORITY);
 
-	chdir("/");
-	umask(022);
-	setsid();
+	pthread_attr_init(&thread_attr);
+
+	/* To create many threads on 32-bit, it may be necessary to explicitly limit the stack size.
+
+	   udevd doesn't use crazy recursion or deep call-chains.
+	   But it does allocate quite a few buffers and temporary strings on the stack.
+	   We may also need extra space for exotic NSS modules (user/group lookup, e.g. over LDAP).
+	   Make a generous guess, double it, and double it again!
+
+	   This comes to just over 200Kb.  The default on i386 is 2Mb.
+	 */
+	stacksize = PTHREAD_STACK_MIN;
+	stacksize += UTIL_PATH_SIZE * 8;
+	stacksize += UTIL_LINE_SIZE * 8;
+	stacksize += UTIL_NAME_SIZE * 8;
+	stacksize += 4096 * 8;
+	stacksize *= 4;
+
+	/* Round up to a whole number of pages */
+	pagesize = sysconf(_SC_PAGESIZE);
+	stacksize = ((stacksize / pagesize) + 1) * pagesize;
+	pthread_attr_setstacksize(&thread_attr, stacksize);
 
 	/* OOM_DISABLE == -17 */
 	fd = open("/proc/self/oom_adj", O_RDWR);
@@ -887,12 +865,14 @@
 	maxfd = udev_ctrl_get_fd(udev_ctrl);
 	maxfd = UDEV_MAX(maxfd, udev_monitor_get_fd(kernel_monitor));
 	maxfd = UDEV_MAX(maxfd, signal_pipe[READ_END]);
+	maxfd = UDEV_MAX(maxfd, event_done_pipe[READ_END]);
 	maxfd = UDEV_MAX(maxfd, inotify_fd);
 	while (!udev_exit) {
 		int fdcount;
 
 		FD_ZERO(&readfds);
 		FD_SET(signal_pipe[READ_END], &readfds);
+		FD_SET(event_done_pipe[READ_END], &readfds);
 		FD_SET(udev_ctrl_get_fd(udev_ctrl), &readfds);
 		FD_SET(udev_monitor_get_fd(kernel_monitor), &readfds);
 		if (inotify_fd >= 0)
@@ -931,6 +911,21 @@
 			read(signal_pipe[READ_END], &buf, sizeof(buf));
 		}
 
+		/* processed events */
+		if (FD_ISSET(event_done_pipe[READ_END], &readfds)) {
+			struct udev_event *buf[32];
+			ssize_t count;
+			unsigned i;
+
+			count = read(event_done_pipe[READ_END], &buf, sizeof(buf));
+			if (count < 0) {
+				err(udev, "read error on thread pipe: %m\n");
+			} else {
+				for (i = 0; i < count / sizeof(buf[0]); i++)
+					udev_done(buf[i]);
+			}
+		}
+
 		/* rules directory inotify watch */
 		if ((inotify_fd >= 0) && FD_ISSET(inotify_fd, &readfds)) {
 			int nbytes;
@@ -963,11 +958,6 @@
 			}
 		}
 
-		if (sigchilds_waiting) {
-			sigchilds_waiting = 0;
-			reap_sigchilds();
-		}
-
 		if (run_exec_q) {
 			run_exec_q = 0;
 			if (!stop_exec_q)
@@ -976,8 +966,19 @@
 	}
 	cleanup_queue_dir(udev);
 	rc = 0;
+	/* Kill event threads before destroying global udev context */
+	if (!udev_list_is_empty(&event_list)) {
+		struct udev_list_node *loop;
+
+		udev_list_node_foreach(loop, &event_list) {
+			struct udev_event *loop_event = node_to_event(loop);
+
+			event_thread_kill(loop_event);
+		}
+	}
 exit:
 	udev_rules_unref(rules);
+	pthread_attr_destroy(&thread_attr);
 	if (signal_pipe[READ_END] >= 0)
 		close(signal_pipe[READ_END]);
 	if (signal_pipe[WRITE_END] >= 0)
@@ -986,6 +987,7 @@
 	if (inotify_fd >= 0)
 		close(inotify_fd);
 	udev_monitor_unref(kernel_monitor);
+	udev_exec_cleanup(udev);
 	udev_selinux_exit(udev);
 	udev_unref(udev);
 	logging_close();


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