On Mon, Feb 05, 2024 at 01:46:36PM +0100, Martin Wilck wrote:
> If a map reload happens while udev is processing rules for a coldplug
> event, DM_SUSPENDED may be set if the respective test in 10-dm.rules
> happens while the device is suspened. This will cause the rules for all
> higher block device layers to be skipped. Record this situation in an udev
> property. The reload operation will trigger another "change" uevent later,
> which would normally be treated as a reload, and be ignored without
> rescanning the device. If a previous "coldplug while suspended" situation is
> detected, perform a full device rescan instead.
For what it's worth, this seems reasonable. But I do see the issue you
pointed out where we can't trust DM_SUSPENDED. Perhaps we could track
in multipathd if an add event occured for a path between when we issued
a reload, and when we got the change event (unfortunately, change events
can occur for things other than reloads that multipathd triggers, and
the only way I know to accurately associate a uevent with a reload is by
using dm udev cookies. We have those turned off in multipathd and I
think it would be a good bit of work to turn them back on without
causing lots of waiting with locks held in multipathd).
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> multipath/11-dm-mpath.rules | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/multipath/11-dm-mpath.rules b/multipath/11-dm-mpath.rules
> index 8fc4a6f..2706809 100644
> --- a/multipath/11-dm-mpath.rules
> +++ b/multipath/11-dm-mpath.rules
> @@ -9,8 +9,13 @@ ENV{DM_ACTION}=="PATH_*", GOTO="check_ready"
>
> ENV{DM_UDEV_DISABLE_OTHER_RULES_FLAG}!="?*", IMPORT{db}="DM_UDEV_DISABLE_OTHER_RULES_FLAG"
> ENV{DM_NOSCAN}!="?*", IMPORT{db}="DM_NOSCAN"
> -GOTO="scan_import"
>
> +# Coldplug event while device is suspended (e.g. during a reload)
> +ACTION=="add", ENV{DM_ACTIVATION}=="1", ENV{DM_SUSPENDED}=="1", \
> + PROGRAM="/bin/logger -t 11-dm-mpath.rules -p daemon.warning \"Coldplug event for suspended device\"", \
> + ENV{DM_COLDPLUG_SUSPENDED}="1"
> +
> +GOTO="scan_import"
> LABEL="check_ready"
>
> IMPORT{db}="DM_DISABLE_OTHER_RULES_FLAG_OLD"
> @@ -53,6 +58,16 @@ ENV{DM_ACTION}=="PATH_FAILED", GOTO="mpath_action"
> ENV{MPATH_DEVICE_READY}="1"
>
> LABEL="mpath_action"
> +
> +# A previous coldplug event occured while the device was suspended.
> +# Activation might have been partially skipped. Activate the device now,
> +# i.e. disable the MPATH_UNCHANGED logic and set DM_ACTIVATION=1.
> +IMPORT{db}="DM_COLDPLUG_SUSPENDED"
> +ENV{DM_COLDPLUG_SUSPENDED}=="1", ENV{DM_SUSPENDED}!="1", \
> + ENV{DM_ACTIVATION}="1", ENV{MPATH_UNCHANGED}="0", \
> + PROGRAM="/bin/logger -t 11-dm-mpath.rules -p daemon.notice \"Forcing activation of previously suspended device\"", \
> + GOTO="force_activation"
> +
> # DM_SUBSYSTEM_UDEV_FLAG0 is the "RELOAD" flag for multipath subsystem.
> # Drop the DM_ACTIVATION flag here as mpath reloads tables if any of its
> # paths are lost/recovered. For any stack above the mpath device, this is not
> @@ -67,6 +82,8 @@ ENV{DM_SUBSYSTEM_UDEV_FLAG0}=="1", \
> ENV{DM_ACTION}=="PATH_FAILED|PATH_REINSTATED", \
> ENV{DM_ACTIVATION}="0", ENV{MPATH_UNCHANGED}="1"
>
> +LABEL="force_activation"
> +
> # Do not initiate scanning if no path is available,
> # otherwise there would be a hang or IO error on access.
> # We'd like to avoid this, especially within udev processing.
> @@ -103,6 +120,9 @@ IMPORT{db}="ID_PART_GPT_AUTO_ROOT"
>
> LABEL="import_end"
>
> +# Reset previous DM_COLDPLUG_SUSPENDED if activation happens now
> +ENV{DM_SUSPENDED}!="1", ENV{DM_ACTIVATION}=="1", ENV{DM_COLDPLUG_SUSPENDED}=""
> +
> # Multipath maps should take precedence over their members.
> ENV{DM_UDEV_LOW_PRIORITY_FLAG}!="1", OPTIONS+="link_priority=50"
>
> --
> 2.43.0
