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