[PATCH storage 3/3] lvm plugin: do not hold inherited locks in cleanup workers

["Michael Köppl" <m.koeppl@proxmox.com>]

The LVM plugin forks its own cleanup workers when rolling back or
deleting snapshots of qcow2 volumes and after failed imports. Like the
worker forked by vdisk_free(), they inherit the locks of their caller
and keep them held until the cleanup is done. This can happen, e.g.,
when restoring a backup over an existing VM with a qcow2 snapshot on LVM
and a disk excluded from the backup, which deletes that disk's snapshot
while holding the config lock. After the restore has finished, changing
or starting the VM then fails with a lock timeout until the cleanup is
done.

Close the inherited lock handles at the start of these workers too.

Since the cleanup worker of a rollback no longer holds the guest
migration lock, another rollback of the same volume can start while the
previous volume is still being wiped. Renaming the current volume to
del-<name> then fails, but only after the guest was already locked for
the rollback, leaving it locked. Check in volume_rollback_is_possible()
that del-<name> does not exist, so such a rollback is refused before the
guest is locked.

Signed-off-by: Michael Köppl <m.koeppl@proxmox.com>
---
 src/PVE/Storage/LVMPlugin.pm | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/PVE/Storage/LVMPlugin.pm b/src/PVE/Storage/LVMPlugin.pm
index a6a5eb70..f9e6936f 100644
--- a/src/PVE/Storage/LVMPlugin.pm
+++ b/src/PVE/Storage/LVMPlugin.pm
@@ -50,7 +50,15 @@ my sub fork_cleanup_worker {
     return if !$cleanup_worker;
     my $rpcenv = PVE::RPCEnvironment::get();
     my $authuser = $rpcenv->get_user();
-    $rpcenv->fork_worker('imgdel', undef, $authuser, $cleanup_worker);
+    $rpcenv->fork_worker(
+        'imgdel',
+        undef,
+        $authuser,
+        sub {
+            PVE::Tools::close_inherited_lock_handles();
+            $cleanup_worker->(@_);
+        },
+    );
 }
 
 sub lvm_pv_info {
@@ -1645,6 +1653,12 @@ sub volume_rollback_is_possible {
     die "can't rollback, '$snap' is not most recent snapshot on '$volname'\n"
         if scalar($blockers->@*) > 0;
 
+    my $vg = $scfg->{vgname};
+    my $name = ($class->parse_volname($volname))[1];
+    my $lvs = lvm_list_volumes($vg);
+    die "can't rollback, previous volume '$vg/del-$name' is still being removed\n"
+        if $lvs->{$vg}->{"del-$name"};
+
     return 1;
 }
 
-- 
2.47.3