anitazha / rpms / systemd

Forked from rpms/systemd 3 years ago
Clone
1ff636
From 175c446fc5ca6adbeeb25dfe0ef725e2f1914259 Mon Sep 17 00:00:00 2001
1ff636
From: Tom Gundersen <teg@jklm.no>
1ff636
Date: Mon, 9 Mar 2015 16:16:23 +0100
1ff636
Subject: [PATCH] udevd: close race in udev settle
1ff636
1ff636
The udev-settle guarantees that udevd is no longer processing any of the
1ff636
events casued by udev-trigger. The way this works is that it sends a
1ff636
synchronous PING to udevd after udev-trigger has ran, and when that returns
1ff636
it knows that udevd has started processing the events from udev-trigger.
1ff636
udev-settle will then wait for the event queue to empty before returning.
1ff636
1ff636
However, there was a race here, as we would only update the /run state at
1ff636
the beginning of the event loop, before reading out new events and before
1ff636
processing the ping.
1ff636
1ff636
That means that if the first uevent arrived in the same event-loop iteration
1ff636
as the PING, we would return the ping before updating the queue state in /run
1ff636
(which would happen on the next iteration).
1ff636
1ff636
The race window here is tiny (as the /run state would probably get updated
1ff636
before udev-settle got a chance to read /run), but still a possibility.
1ff636
1ff636
Fix the problem by updating the /run state as the last step before returning
1ff636
the PING.
1ff636
1ff636
We must still update it at the beginning of the loop as well, otherwise we
1ff636
risk being stuck in poll() with a stale state in /run.
1ff636
1ff636
Reported-by: Daniel Drake <drake@endlessm.com>
1ff636
(cherry picked from commit db93e063bdffe0a8b95fcc522aeacddf62d1a9f9)
1ff636
---
1ff636
 src/udev/udevd.c | 26 +++++++++++++++++---------
1ff636
 1 file changed, 17 insertions(+), 9 deletions(-)
1ff636
1ff636
diff --git a/src/udev/udevd.c b/src/udev/udevd.c
181b3f
index 99d4c8983..e98c1fd6d 100644
1ff636
--- a/src/udev/udevd.c
1ff636
+++ b/src/udev/udevd.c
1ff636
@@ -909,6 +909,17 @@ static void handle_signal(struct udev *udev, int signo) {
1ff636
         }
1ff636
 }
1ff636
 
1ff636
+static void event_queue_update(void) {
1ff636
+        if (!udev_list_node_is_empty(&event_list)) {
1ff636
+                int fd;
1ff636
+
1ff636
+                fd = open("/run/udev/queue", O_WRONLY|O_CREAT|O_CLOEXEC|O_TRUNC|O_NOFOLLOW, 0444);
1ff636
+                if (fd >= 0)
1ff636
+                       close(fd);
1ff636
+        } else
1ff636
+                unlink("/run/udev/queue");
1ff636
+}
1ff636
+
1ff636
 static int systemd_fds(struct udev *udev, int *rctrl, int *rnetlink) {
1ff636
         int ctrl = -1, netlink = -1;
1ff636
         int fd, n;
1ff636
@@ -1369,15 +1380,7 @@ int main(int argc, char *argv[]) {
1ff636
                 }
1ff636
 
1ff636
                 /* tell settle that we are busy or idle */
1ff636
-                if (!udev_list_node_is_empty(&event_list)) {
1ff636
-                        int fd;
1ff636
-
1ff636
-                        fd = open("/run/udev/queue", O_WRONLY|O_CREAT|O_CLOEXEC|O_TRUNC|O_NOFOLLOW, 0444);
1ff636
-                        if (fd >= 0)
1ff636
-                                close(fd);
1ff636
-                } else {
1ff636
-                        unlink("/run/udev/queue");
1ff636
-                }
1ff636
+                event_queue_update();
1ff636
 
1ff636
                 fdcount = epoll_wait(fd_ep, ev, ELEMENTSOF(ev), timeout);
1ff636
                 if (fdcount < 0)
1ff636
@@ -1502,6 +1505,11 @@ int main(int argc, char *argv[]) {
1ff636
                 if (is_inotify)
1ff636
                         handle_inotify(udev);
1ff636
 
1ff636
+                /* tell settle that we are busy or idle, this needs to be before the
1ff636
+                 * PING handling
1ff636
+                 */
1ff636
+                event_queue_update();
1ff636
+
1ff636
                 /*
1ff636
                  * This needs to be after the inotify handling, to make sure,
1ff636
                  * that the ping is send back after the possibly generated