Commit d23b5c577715 ("cgroup: Make operations on the cgroup root_list RCU
safe") adds a new rcu_head to the cgroup_root structure and kvfree_rcu()
for freeing the cgroup_root.
The use of kvfree_rcu(), however, has the limitation that the offset of
the rcu_head structure within the larger data structure cannot exceed
4096 or the compilation will fail. By putting rcu_head below the cgroup
structure, any change to the cgroup structure that makes it larger has
the risk of build failure. Commit 77070eeb8821 ("cgroup: Avoid false
cacheline sharing of read mostly rstat_cpu") happens to be the commit
that breaks it even though it is not its fault. Fix it by moving the
rcu_head structure up before the cgroup structure.
Fixes: d23b5c577715 ("cgroup: Make operations on the cgroup root_list RCU safe")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
include/linux/cgroup-defs.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 5a97ea95b564..45359969d8cf 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -562,6 +562,10 @@ struct cgroup_root {
/* Unique id for this hierarchy. */
int hierarchy_id;
+ /* A list running through the active hierarchies */
+ struct list_head root_list;
+ struct rcu_head rcu;
+
/*
* The root cgroup. The containing cgroup_root will be destroyed on its
* release. cgrp->ancestors[0] will be used overflowing into the
@@ -575,10 +579,6 @@ struct cgroup_root {
/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
atomic_t nr_cgrps;
- /* A list running through the active hierarchies */
- struct list_head root_list;
- struct rcu_head rcu;
-
/* Hierarchy-specific flags */
unsigned int flags;
--
2.39.3
