Re: [PATCH] multipathd: fix hang during shutdown with queuing maps

[Benjamin Marzinski <bmarzins@redhat.com>]

On Thu, Feb 27, 2025 at 06:41:04PM +0100, Martin Wilck wrote:
> Since c9689b6 ("multipathd: Remove dependency on
> systemd-udev-settle.service"), multipathd.service starts very early during
> boot, which in systemd's service ordering logic means that it is stopped
> late. While this is generally a good thing, it means that, when systemd
> unmounts file systems and tears down the block device stack, multipathd
> is still running. Therefore our "queue_without_daemon" logic, which disables
> queuing when multipathd exits, isn't effective yet. If there are any
> multipath maps that are in queueing state at this point in time, the system
> may hang indefinitely.
> 
> To fix that, add a new service which starts later (and thus stops earlier) and
> disables queueing on all multipath maps during shutdown. Similar to lvm2's
> blk-availability.service, the service does nothing when started.
> 
> Fixes: c9689b6 ("multipathd: Remove dependency on systemd-udev-settle.service")

Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  multipathd/Makefile                       | 6 ++++--
>  multipathd/multipathd-queueing.service.in | 9 +++++++++
>  multipathd/multipathd.service.in          | 2 +-
>  3 files changed, 14 insertions(+), 3 deletions(-)
>  create mode 100644 multipathd/multipathd-queueing.service.in
> 
> diff --git a/multipathd/Makefile b/multipathd/Makefile
> index 61cf1af..4bcee6b 100644
> --- a/multipathd/Makefile
> +++ b/multipathd/Makefile
> @@ -41,7 +41,7 @@ ifeq ($(FPIN_SUPPORT),1)
>  OBJS += fpin_handlers.o
>  endif
>  
> -all : $(EXEC) $(CLI) $(MANPAGES) $(EXEC).service $(EXEC).socket
> +all : $(EXEC) $(CLI) $(MANPAGES) $(EXEC).service $(EXEC).socket $(EXEC)-queueing.service
>  
>  $(EXEC): $(OBJS) $(multipathdir)/libmultipath.so $(mpathcmddir)/libmpathcmd.so
>  	@echo building $@ because of $?
> @@ -64,6 +64,7 @@ install:
>  ifdef SYSTEMD
>  	$(Q)$(INSTALL_PROGRAM) -d $(DESTDIR)$(unitdir)
>  	$(Q)$(INSTALL_PROGRAM) -m 644 $(EXEC).service $(DESTDIR)$(unitdir)
> +	$(Q)$(INSTALL_PROGRAM) -m 644 $(EXEC)-queueing.service $(DESTDIR)$(unitdir)
>  	$(Q)$(INSTALL_PROGRAM) -m 644 $(EXEC).socket $(DESTDIR)$(unitdir)
>  endif
>  	$(Q)$(INSTALL_PROGRAM) -d $(DESTDIR)$(mandir)/man8
> @@ -74,11 +75,12 @@ uninstall:
>  	$(Q)$(RM) $(DESTDIR)$(bindir)/$(EXEC) $(DESTDIR)$(bindir)/$(CLI)
>  	$(Q)$(RM) $(DESTDIR)$(mandir)/man8/$(EXEC).8
>  	$(Q)$(RM) $(DESTDIR)$(mandir)/man8/$(CLI).8
> +	$(Q)$(RM) $(DESTDIR)$(unitdir)/$(EXEC)-queueing.service
>  	$(Q)$(RM) $(DESTDIR)$(unitdir)/$(EXEC).service
>  	$(Q)$(RM) $(DESTDIR)$(unitdir)/$(EXEC).socket
>  
>  clean: dep_clean
> -	$(Q)$(RM) core *.o $(EXEC) $(CLI) $(MANPAGES) $(EXEC).service $(EXEC).socket
> +	$(Q)$(RM) core *.o $(EXEC) $(CLI) $(MANPAGES) $(EXEC).service $(EXEC)-queueing.service $(EXEC).socket
>  
>  include $(wildcard $(OBJS:.o=.d) $(CLI_OBJS:.o=.d))
>  
> diff --git a/multipathd/multipathd-queueing.service.in b/multipathd/multipathd-queueing.service.in
> new file mode 100644
> index 0000000..18b0ca6
> --- /dev/null
> +++ b/multipathd/multipathd-queueing.service.in
> @@ -0,0 +1,9 @@
> +[Unit]
> +Description=Enable queuing for multipath maps
> +After=local-fs.target remote-fs.target multipathd.service
> +
> +[Service]
> +Type=oneshot
> +RemainAfterExit=yes
> +ExecStart=/bin/true
> +ExecStop=@BINDIR@/multipathd disablequeueing maps
> diff --git a/multipathd/multipathd.service.in b/multipathd/multipathd.service.in
> index b6a25b3..eb58943 100644
> --- a/multipathd/multipathd.service.in
> +++ b/multipathd/multipathd.service.in
> @@ -2,7 +2,7 @@
>  Description=Device-Mapper Multipath Device Controller
>  Before=lvm2-activation-early.service
>  Before=local-fs-pre.target blk-availability.service shutdown.target
> -Wants=systemd-udevd-kernel.socket @MODPROBE_UNIT@
> +Wants=systemd-udevd-kernel.socket multipathd-queueing.service @MODPROBE_UNIT@
>  After=systemd-udevd-kernel.socket @MODPROBE_UNIT@
>  After=multipathd.socket systemd-remount-fs.service
>  Before=initrd-cleanup.service
> -- 
> 2.48.1