tools: add -b/--background for pvscan --cache -aay

Udev daemon has recently introduced a limit on the number of udev
processes (there was no limit before). This causes a problem
when calling pvscan --cache -aay in lvmetad udev rules which
is supposed to activate the volumes. This activation is itself
synced with udev and so it waits for the activation to complete
before the pvscan finishes. The event processing can't continue
until this pvscan call is finished.

But if we're at the limit with the udev process count, we can't
instatiate any more udev processes, all such events are queued
and so we can't process the lvm activation event for which the
pvscan is waiting.

Then we're in a deadlock since the udev process with the
pvscan --cache -aay call waits for the lvm activation udev
processing to complete, but that will never happen as there's
this limit hit with the number of udev processes.

The process with pvscan --cache -aay actually times out eventually
(3min or 30sec, depends on the version of udev).

This patch makes it possible to run the pvscan --cache -aay
in the background so the udev processing can continue and hence
we can avoid the deadlock mentioned above.

1 files changed, 1 insertions, 1 deletions

diff --git a/udev/69-dm-lvm-metad.rules.in b/udev/69-dm-lvm-metad.rules.in
index 2d6720e6a..6162e262f 100644
--- a/udev/69-dm-lvm-metad.rules.in
+++ b/udev/69-dm-lvm-metad.rules.in
@@ -34,6 +34,6 @@ KERNEL!="dm-[0-9]*", ACTION!="add", GOTO="lvm_end"
 KERNEL=="dm-[0-9]*", ENV{DM_ACTIVATION}!="1", GOTO="lvm_end"
 
 LABEL="lvm_scan"
-RUN+="(LVM_EXEC)/lvm pvscan --cache --activate ay --major $major --minor $minor"
+RUN+="(LVM_EXEC)/lvm pvscan --background --cache --activate ay --major $major --minor $minor"
 
 LABEL="lvm_end"