Hi On Tue, Apr 7, 2015 at 12:03 AM, Daniel Drake <dr...@endlessm.com> wrote: > udev uses inotify to implement a scheme where when the user closes > a writable device node, a change uevent is forcefully generated. > In the case of block devices, it actually requests a partition rescan. > > This currently can't be synchronized with "udevadm settle", i.e. this > is not reliable in a script: > > sfdisk --change-id /dev/sda 1 81 > udevadm settle > mount /dev/sda1 /foo > > The settle call doesn't synchronize there, so at the same time we try > to mount the device, udevd is busy removing the partition device nodes and > readding them again. The mount call often happens in that moment where the > partition node has been removed but not readded yet. > > This exact issue was fixed long ago: > http://git.kernel.org/cgit/linux/hotplug/udev.git/commit/?id=bb38678e3ccc02bcd970ccde3d8166a40edf92d3 > > but that fix is no longer valid now that sequence numbers are no longer > used. > > Fix this by forcing another mainloop iteration after handling inotify events > before unblocking settle. If the inotify event caused us to generate a > "change" event, we'll pick that up in the following loop iteration, before > we reach the end of the loop where we respond to settle's control message, > unblocking it. > --- > src/udev/udevd.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/src/udev/udevd.c b/src/udev/udevd.c > index 830aedd..dfecef8 100644 > --- a/src/udev/udevd.c > +++ b/src/udev/udevd.c > @@ -1504,9 +1504,22 @@ int main(int argc, char *argv[]) { > continue; > > /* device node watch */ > - if (is_inotify) > + if (is_inotify) { > handle_inotify(udev); > > + /* > + * settle might be waiting on us to determine the > queue > + * state. If we just handled an inotify event, we > might have > + * generated a "change" event, but we won't have > queued up > + * the resultant uevent yet. > + * > + * Before we go ahead and potentially tell settle > that the > + * queue is empty, lets loop one more time to update > the > + * queue state again before deciding. > + */ > + continue; > + } > +
Nice catch! There's indeed a small race between handling inotify and queuing up the change-event. We need to re-loop there. One day we should switch to sd-event to avoid such bugs... I mean the symptom is inherent to queuing up events while handling them. Meh! Applied! Thanks David > /* tell settle that we are busy or idle, this needs to be > before the > * PING handling > */ > -- > 2.1.0 > > _______________________________________________ > systemd-devel mailing list > systemd-devel@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/systemd-devel _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
