2:20 a.m.
I've encountered the following bug, but only on Gentoo with
systemd and CGroupsV2. I've started an LXC container successfully
but destroying it reported the following error:
error: Failed to destroy domain 'amd64'
error: internal error: failed to get cgroup backend for 'pathOfController'
Debugging showed, that CGroup hierarchy is full of surprises:
/sys/fs/cgroup/machine.slice/machine-lxc\x2d861\x2damd64.scope/
└── libvirt
├── dev-hugepages.mount
├── dev-mqueue.mount
├── init.scope
├── sys-fs-fuse-connections.mount
├── sys-kernel-config.mount
├── sys-kernel-debug.mount
├── sys-kernel-tracing.mount
├── system.slice
│ ├── console-getty.service
│ ├── dbus.service
│ ├── system-getty.slice
│ ├── system-modprobe.slice
│ ├── systemd-journald.service
│ ├── systemd-logind.service
│ └── tmp.mount
└── user.slice
For comparison, here's the same container on recent Rawhide:
/sys/fs/cgroup/machine.slice/machine-lxc\x2d13550\x2damd64.scope/
└── libvirt
Anyway, those nested directories should not be a problem, because
virCgroupKillRecursiveInternal() removes them recursively, right?
Sort of. The function really does remove nested directories, but
it assumes that every directory has the same controller as the
rest. Just take a look at virCgroupV2KillRecursive() - it gets
'Any' controller (the first one it found in ".scope") and then
passes it to virCgroupKillRecursiveInternal().
This assumption is not true though. The controllers found in
".scope" are the following:
cpuset cpu io memory pids
while "libvirt" has fewer:
cpuset cpu io memory
Up until now it's not problem, because of how we order
controllers internally - "cpu" is the first and thus picking
"Any" controller returns just that. But the rest of directories
has no controllers, their "cgroup.controllers" is just empty.
What fixes the bug is dropping @controller argument from
virCgroupKillRecursiveInternal() and letting each iteration work
pick its own controller.
Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
---
src/util/vircgroup.c | 25 +++++++++++++++++++++++--
src/util/vircgrouppriv.h | 1 -
src/util/vircgroupv1.c | 7 +------
src/util/vircgroupv2.c | 7 +------
4 files changed, 25 insertions(+), 15 deletions(-)
diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
index 96280a0a4e..37dde2a5ed 100644
--- a/src/util/vircgroup.c
+++ b/src/util/vircgroup.c
@@ -1477,6 +1477,24 @@ virCgroupHasController(virCgroup *cgroup, int controller)
}
+static int
+virCgroupGetAnyController(virCgroup *cgroup)
+{
+ size_t i;
+
+ for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
+ if (!cgroup->backends[i])
+ continue;
+
+ return cgroup->backends[i]->getAnyController(cgroup);
+ }
+
+ virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+ _("Unable to get any controller"));
+ return -1;
+}
+
+
int
virCgroupPathOfController(virCgroup *group,
unsigned int controller,
@@ -2715,11 +2733,11 @@ int
virCgroupKillRecursiveInternal(virCgroup *group,
int signum,
GHashTable *pids,
- int controller,
const char *taskFile,
bool dormdir)
{
int rc;
+ int controller;
bool killedAny = false;
g_autofree char *keypath = NULL;
g_autoptr(DIR) dp = NULL;
@@ -2728,6 +2746,9 @@ virCgroupKillRecursiveInternal(virCgroup *group,
VIR_DEBUG("group=%p signum=%d pids=%p taskFile=%s dormdir=%d",
group, signum, pids, taskFile, dormdir);
+ if ((controller = virCgroupGetAnyController(group)) < 0)
+ return -1;
+
if (virCgroupPathOfController(group, controller, "", &keypath) < 0)
return -1;
@@ -2760,7 +2781,7 @@ virCgroupKillRecursiveInternal(virCgroup *group,
return -1;
if ((rc = virCgroupKillRecursiveInternal(subgroup, signum, pids,
- controller, taskFile, true)) < 0)
+ taskFile, true)) < 0)
return -1;
if (rc == 1)
killedAny = true;
diff --git a/src/util/vircgrouppriv.h b/src/util/vircgrouppriv.h
index 00193fb101..caf7ed84db 100644
--- a/src/util/vircgrouppriv.h
+++ b/src/util/vircgrouppriv.h
@@ -135,6 +135,5 @@ int virCgroupRemoveRecursively(char *grppath);
int virCgroupKillRecursiveInternal(virCgroup *group,
int signum,
GHashTable *pids,
- int controller,
const char *taskFile,
bool dormdir);
diff --git a/src/util/vircgroupv1.c b/src/util/vircgroupv1.c
index 2cc7dd386a..8a04bb2e4a 100644
--- a/src/util/vircgroupv1.c
+++ b/src/util/vircgroupv1.c
@@ -812,12 +812,7 @@ virCgroupV1KillRecursive(virCgroup *group,
int signum,
GHashTable *pids)
{
- int controller = virCgroupV1GetAnyController(group);
-
- if (controller < 0)
- return -1;
-
- return virCgroupKillRecursiveInternal(group, signum, pids, controller,
+ return virCgroupKillRecursiveInternal(group, signum, pids,
"tasks", false);
}
diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
index e555217355..8881d3a88a 100644
--- a/src/util/vircgroupv2.c
+++ b/src/util/vircgroupv2.c
@@ -577,12 +577,7 @@ virCgroupV2KillRecursive(virCgroup *group,
int signum,
GHashTable *pids)
{
- int controller = virCgroupV2GetAnyController(group);
-
- if (controller < 0)
- return -1;
-
- return virCgroupKillRecursiveInternal(group, signum, pids, controller,
+ return virCgroupKillRecursiveInternal(group, signum, pids,
"cgroup.threads", false);
}
--
2.26.3