From ae3dadc1d2a08070e596c1603797ea85aa1bd90f Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Thu, 7 Dec 2023 08:46:14 -0500 Subject: [PATCH] cgroup: Move rcu_head up near the top of cgroup_root MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit commit a7fb0423c201ba12815877a0b5a68a6a1710b23a upstream. 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 current implementation of kvfree_rcu(), however, has the limitation that the offset of the rcu_head structure within the larger data structure must be less than 4096 or the compilation will fail. See the macro definition of __is_kvfree_rcu_offset() in include/linux/rcupdate.h for more information. By putting rcu_head below the large cgroup structure, any change to the cgroup structure that makes it larger run the risk of causing build failure under certain configurations. Commit 77070eeb8821 ("cgroup: Avoid false cacheline sharing of read mostly rstat_cpu") happens to be the last straw that breaks it. Fix this problem by moving the rcu_head structure up before the cgroup structure. Fixes: d23b5c577715 ("cgroup: Make operations on the cgroup root_list RCU safe") Reported-by: Stephen Rothwell Closes: https://lore.kernel.org/lkml/20231207143806.114e0a74@canb.auug.org.au/ Signed-off-by: Waiman Long Acked-by: Yafang Shao Reviewed-by: Yosry Ahmed Reviewed-by: Michal Koutný Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman Gbp-Pq: Topic bugfix/all Gbp-Pq: Name cgroup-move-rcu_head-up-near-the-top-of-cgroup_root.patch --- 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 e0e03c68000..c1bf210fe71 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -501,6 +501,10 @@ 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; /* Must be near the top */ + /* The root cgroup. Root is destroyed on its release. */ struct cgroup cgrp; @@ -510,10 +514,6 @@ 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; -- 2.30.2