Re: [PATCH] multipath.rules.in: fix race in unit cancel-multipath-wait-$kernel

[Benjamin Marzinski <bmarzins@redhat.com>]

On Fri, Aug 28, 2026 at 03:57:38PM +0200, Martin Wilck wrote:
> @Ben and others, I wasn't certain about this at first. Below is my flow
> of thoughts from the SUSE bugzilla, through which I came to think that
> it's correct. But this is quite subtle, so please give it some own
> thoughts ;-)
> 
> Martin
> 
> IIUC, if the "Conflicts" is removed, the timer unit will continue
> running through the switch root phase, and will be taken up by systemd
> through serialization 

But like Antonio said, isolate will stop the timer, since it's not a
dependency of initrd-switch-root.target, right? I'm a little fuzzy on
exactly how all the units get stopped, and you might be right that a
udev rule could run and trigger a timer after the isolate could catch
it. But I think you are right that this would be harmless if it could
occur.

-Ben

> 
> [*] upstream dracut version history related to multipathd.socket:
> 
> 247d2b ("fix(multipathd.service): adapt to upstream multipath-tools
> unit file") (dracut 056) added socket dep to the multipathd.service
> unit file.
> 02e646f ("fix(multipath): install multipathd.socket") (dracut 058) made
> sure the socket unit file was installed.
> 297525c ("fix(multipath): remove dependency on multipathd.socket")
> (dracut 060) removed both
> 
> 5e87b68 ("refactor(multipath): remove custom multipathd.service")
> (dracut 107) removed the .service file.
> 
> > ---
> >  multipath/multipath.rules.in | 14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/multipath/multipath.rules.in
> > b/multipath/multipath.rules.in
> > index 2ac1972f..7b605dd4 100644
> > --- a/multipath/multipath.rules.in
> > +++ b/multipath/multipath.rules.in
> > @@ -68,8 +68,18 @@ ENV{.SAVED_FM_WAIT_UNTIL}=="?*",
> > GOTO="pretend_mpath"
> >  # the --on-active timeout.
> >  #
> >  # We must trigger an "add" event because LVM2 will only act on
> > those.
> > -
> > -RUN+="@SYSDIR_BIN@/systemd-run --unit=cancel-multipath-wait-$kernel
> > --description 'cancel waiting for multipath siblings of $kernel' --
> > no-block --timer-property DefaultDependencies=no --timer-property
> > Conflicts=shutdown.target --timer-property Before=shutdown.target --
> > timer-property Conflicts=initrd-cleanup.service --timer-property
> > Before=initrd-cleanup.service --timer-property AccuracySec=500ms --
> > property DefaultDependencies=no --property Conflicts=shutdown.target
> > --property Before=shutdown.target --property Conflicts=initrd-
> > cleanup.service --property Before=initrd-cleanup.service --on-
> > active=$env{FIND_MULTIPATHS_WAIT_UNTIL} @SYSDIR_BIN@/udevadm trigger
> > --action=add $sys$devpath"
> > +#
> > +# These units are ordered Before=initrd-cleanup.service so that a
> > trigger that
> > +# is already in flight completes before the initrd switches root.
> > They must
> > +# *not* use Conflicts=initrd-cleanup.service: unlike
> > shutdown.target, whose
> > +# jobs are enqueued irreversibly, initrd-cleanup.service/start is a
> > plain job
> > +# enqueued by initrd-parse-etc.service via OnSuccess=. Starting a
> > unit that
> > +# conflicts with it therefore cancels that job instead of failing to
> > start,
> > +# and OnSuccess= is never retried, so the initrd would hang forever
> > with an
> > +# empty job queue. Stopping these units before switch-root is
> > already
> > +# guaranteed by the isolate to initrd-switch-root.target.
> > +
> > +RUN+="@SYSDIR_BIN@/systemd-run --unit=cancel-multipath-wait-$kernel
> > --description 'cancel waiting for multipath siblings of $kernel' --
> > no-block --timer-property DefaultDependencies=no --timer-property
> > Conflicts=shutdown.target --timer-property Before=shutdown.target --
> > timer-property Before=initrd-cleanup.service --timer-property
> > AccuracySec=500ms --property DefaultDependencies=no --property
> > Conflicts=shutdown.target --property Before=shutdown.target --
> > property Before=initrd-cleanup.service --on-
> > active=$env{FIND_MULTIPATHS_WAIT_UNTIL} @SYSDIR_BIN@/udevadm trigger
> > --action=add $sys$devpath"
> >  
> >  LABEL="pretend_mpath"
> >  ENV{DM_MULTIPATH_DEVICE_PATH}="1"
> 
> -- 
> Dr. Martin Wilck <mwilck@suse.com>
> SUSE Software Solutions Germany GmbH, Frankenstr. 146, 90461 Nürnberg,
> Germany
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