chiark / gitweb /
[PATCH] udevd race conditions and performance, assorted cleanups
authorchris_friesen@sympatico.ca <chris_friesen@sympatico.ca>
Thu, 1 Apr 2004 07:03:07 +0000 (23:03 -0800)
committerGreg KH <gregkh@suse.de>
Wed, 27 Apr 2005 04:35:13 +0000 (21:35 -0700)
This patch covers a number of areas:

1) sysfs.h is fixed up to use the common dbg() macro.  This fixes the
case where DEBUG is defined but USE_LOG isn't.

2) udevstart.c is modified to include the proper headers, rather than
getting them indirectly which can break depending on Makefile flags

3) udevd.c gets some major changes:
a) I added a pipe from the signal handler.  This fixes the race
conditions that I mentioned earlier.  Basically, the point of the pipe
is to force the select() call to return immediately if a signal handler
fired before we actually started the select() call.  This then lets us
run the appropriate code based on flags set in the signal handler proper.
b) I added a number of flags to coalesce calls to common routines.  This
should make things slightly more efficient.
c) since most calls will tend to come in with a sequence number larger
than what has been received, I switched msg_queue_insert() to scan the
msg_list backwards to improve performance.

 filename="udevd.diff"

libsysfs/sysfs.h
udevd.c
udevstart.c

index 1b800dd..0fdb38a 100644 (file)
@@ -37,9 +37,7 @@
 #ifdef DEBUG
 #include "../logging.h" 
 #define dprintf(format, arg...)                                                                \
-       do {                                                                            \
-               log_message (LOG_DEBUG , "%s: " format , __FUNCTION__ , ## arg);        \
-       } while (0)
+       dbg(format, ##arg)
 #else
 #define dprintf(format, arg...) do { } while (0)
 #endif
diff --git a/udevd.c b/udevd.c
index 0757dca..3b91a45 100644 (file)
--- a/udevd.c
+++ b/udevd.c
@@ -33,6 +33,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <sys/time.h>
+#include <fcntl.h>
 
 #include "list.h"
 #include "udev.h"
 #include "udevd.h"
 #include "logging.h"
 
+static int pipefds[2];
 static int expected_seqnum = 0;
 volatile static int children_waiting;
-volatile static int msg_q_timeout;
+volatile static int run_msg_q;
+volatile static int sig_flag;
+static int run_exec_q;
 
 static LIST_HEAD(msg_list);
 static LIST_HEAD(exec_list);
@@ -51,6 +55,8 @@ static LIST_HEAD(running_list);
 
 static void exec_queue_manager(void);
 static void msg_queue_manager(void);
+static void user_sighandler(void);
+static void reap_kids(void);
 
 #ifdef LOG
 unsigned char logname[LOGNAME_SIZE];
@@ -66,10 +72,12 @@ void log_message (int level, const char *format, ...)
 
 static void msg_dump_queue(void)
 {
+#ifdef DEBUG
        struct hotplug_msg *msg;
 
        list_for_each_entry(msg, &msg_list, list)
                dbg("sequence %d in queue", msg->seqnum);
+#endif
 }
 
 static void msg_dump(struct hotplug_msg *msg)
@@ -92,7 +100,6 @@ static void run_queue_delete(struct hotplug_msg *msg)
 {
        list_del(&msg->list);
        free(msg);
-       exec_queue_manager();
 }
 
 /* orders the message in the queue by sequence number */
@@ -100,18 +107,20 @@ static void msg_queue_insert(struct hotplug_msg *msg)
 {
        struct hotplug_msg *loop_msg;
 
-       /* sort message by sequence number into list*/
-       list_for_each_entry(loop_msg, &msg_list, list)
-               if (loop_msg->seqnum > msg->seqnum)
+       /* sort message by sequence number into list. events
+        * will tend to come in order, so scan the list backwards
+        */
+       list_for_each_entry_reverse(loop_msg, &msg_list, list)
+               if (loop_msg->seqnum < msg->seqnum)
                        break;
-       list_add_tail(&msg->list, &loop_msg->list);
+       list_add(&msg->list, &loop_msg->list);
        dbg("queued message seq %d", msg->seqnum);
 
        /* store timestamp of queuing */
        msg->queue_time = time(NULL);
 
        /* run msg queue manager */
-       msg_queue_manager();
+       run_msg_q = 1;
 
        return ;
 }
@@ -138,6 +147,9 @@ static void udev_run(struct hotplug_msg *msg)
        case -1:
                dbg("fork of child failed");
                run_queue_delete(msg);
+               /* note: we never managed to run, so we had no impact on 
+                * running_with_devpath(), so don't bother setting run_exec_q
+                */
                break;
        default:
                /* get SIGCHLD in main loop */
@@ -180,7 +192,7 @@ static void exec_queue_manager()
 static void msg_move_exec(struct hotplug_msg *msg)
 {
        list_move_tail(&msg->list, &exec_list);
-       exec_queue_manager();
+       run_exec_q = 1;
        expected_seqnum = msg->seqnum+1;
        dbg("moved seq %d to exec, next expected is %d",
                msg->seqnum, expected_seqnum);
@@ -276,7 +288,7 @@ static void handle_msg(int sock)
        /* if no seqnum is given, we move straight to exec queue */
        if (msg->seqnum == -1) {
                list_add(&msg->list, &exec_list);
-               exec_queue_manager();
+               run_exec_q = 1;
        } else {
                msg_queue_insert(msg);
        }
@@ -289,19 +301,37 @@ skip:
 
 static void sig_handler(int signum)
 {
+       int rc;
        switch (signum) {
                case SIGINT:
                case SIGTERM:
                        exit(20 + signum);
                        break;
                case SIGALRM:
-                       msg_q_timeout = 1;
+                       /* set flag, then write to pipe if needed */
+                       run_msg_q = 1;
+                       goto do_write;
                        break;
                case SIGCHLD:
+                       /* set flag, then write to pipe if needed */
                        children_waiting = 1;
+                       goto do_write;
                        break;
                default:
                        dbg("unhandled signal");
+                       return;
+       }
+       
+do_write:
+       /* if pipe is empty, write to pipe to force select to return
+        * immediately when it gets called
+        */
+       if (!sig_flag) {
+               rc = write(pipefds[1],&signum,sizeof(signum));
+               if (rc < 0)
+                       dbg("unable to write to pipe");
+               else
+                       sig_flag = 1;
        }
 }
 
@@ -314,19 +344,53 @@ static void udev_done(int pid)
                if (msg->pid == pid) {
                        dbg("<== exec seq %d came back", msg->seqnum);
                        run_queue_delete(msg);
+                       
+                       /* we want to run the exec queue manager since there may
+                        * be events waiting with the devpath of the one that
+                        * just finished
+                        */
+                       run_exec_q = 1;
                        return;
                }
        }
 }
 
+static void reap_kids()
+{
+       /* reap all dead children */
+       while(1) {
+               int pid = waitpid(-1, 0, WNOHANG);
+               if ((pid == -1) || (pid == 0))
+                       break;
+               udev_done(pid);
+       }
+}
+
+/* just read everything from the pipe and clear the flag,
+ * the useful flags were set in the signal handler
+ */
+static void user_sighandler()
+{
+       int sig;
+       while(1) {
+               int rc = read(pipefds[0],&sig,sizeof(sig));
+               if (rc < 0)
+                       break;
+
+               sig_flag = 0;
+       }
+}
+
+
 int main(int argc, char *argv[])
 {
-       int ssock;
+       int ssock, maxsockplus;
        struct sockaddr_un saddr;
        socklen_t addrlen;
        int retval;
        const int on = 1;
        struct sigaction act;
+       fd_set readfds;
 
        init_logging("udevd");
        dbg("version %s", UDEV_VERSION);
@@ -335,16 +399,32 @@ int main(int argc, char *argv[])
                dbg("need to be root, exit");
                exit(1);
        }
-
-       /* set signal handler */
+       
+       /* setup signal handler pipe */
+   retval = pipe(pipefds);
+   if (retval < 0) {
+      dbg("error getting pipes: %s", strerror(errno));
+      exit(1);
+   }
+       
+   retval = fcntl(pipefds[0], F_SETFL, O_NONBLOCK);
+   if (retval < 0) {
+      dbg("fcntl on read pipe: %s", strerror(errno));
+      exit(1);
+   }
+   
+   retval = fcntl(pipefds[1], F_SETFL, O_NONBLOCK);
+   if (retval < 0) {
+      dbg("fcntl on write pipe: %s", strerror(errno));
+      exit(1);
+   }
+
+       /* set signal handlers */
        act.sa_handler = sig_handler;
-       sigemptyset (&act.sa_mask);
+       sigemptyset(&act.sa_mask);
        act.sa_flags = SA_RESTART;
        sigaction(SIGINT, &act, NULL);
        sigaction(SIGTERM, &act, NULL);
-
-       /* we want these two to interrupt system calls */
-       act.sa_flags = 0;
        sigaction(SIGALRM, &act, NULL);
        sigaction(SIGCHLD, &act, NULL);
 
@@ -370,23 +450,50 @@ int main(int argc, char *argv[])
        /* enable receiving of the sender credentials */
        setsockopt(ssock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
 
+   FD_ZERO(&readfds);
+   FD_SET(ssock, &readfds);
+   FD_SET(pipefds[0], &readfds);
+       maxsockplus = ssock+1;
        while (1) {
-               handle_msg(ssock);
-
-               while(msg_q_timeout) {
-                       msg_q_timeout = 0;
-                       msg_queue_manager();
+               fd_set workreadfds = readfds;
+               retval = select(maxsockplus, &workreadfds, NULL, NULL, NULL);
+               
+               if (retval < 0) {
+                       dbg("error in select: %s", strerror(errno));
+                       continue;
                }
-
-               while(children_waiting) {
+               
+               if (FD_ISSET(ssock, &workreadfds))
+                       handle_msg(ssock);
+               
+               if (FD_ISSET(pipefds[0], &workreadfds))
+                       user_sighandler();
+               
+               if (children_waiting) {
                        children_waiting = 0;
-                       /* reap all dead children */
-                       while(1) {
-                               int pid = waitpid(-1, 0, WNOHANG);
-                               if ((pid == -1) || (pid == 0))
-                                       break;
-                               udev_done(pid);
+                       reap_kids();
+               }
+               
+               if (run_msg_q) {
+                       run_msg_q = 0;
+                       msg_queue_manager();
+               }
+               
+               if (run_exec_q) {
+                       
+                       /* this is tricky.  exec_queue_manager() loops over exec_list, and
+                        * calls running_with_devpath(), which loops over running_list. This gives
+                        * O(N*M), which can get *nasty*.  Clean up running_list before
+                        * calling exec_queue_manager().
+                        */
+                       
+                       if (children_waiting) {
+                               children_waiting = 0;
+                               reap_kids();
                        }
+
+                       run_exec_q = 0;
+                       exec_queue_manager();
                }
        }
 exit:
index 40dbaf2..eda6355 100644 (file)
@@ -29,6 +29,8 @@
 #include <ctype.h>
 #include <dirent.h>
 #include <sys/wait.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #include "logging.h"