From 047f0ee8b572bfd7a23aee4415035fc50faf56ed Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Mon, 2 Dec 2024 16:40:24 +0530 Subject: [PATCH] cgroup: Move rcu_head up near the top of cgroup_root MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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: Fedor Pchelkin [Shivani: Modified to apply on v5.4.y] Signed-off-by: Shivani Agarwal Reviewed-by: Siddh Raman Pant Signed-off-by: Siddh Raman Pant Signed-off-by: Greg Kroah-Hartman --- 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 c64f11674850..f0798d98be8e 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -506,6 +506,10 @@ 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. Root is destroyed on its release. */ struct cgroup cgrp; @@ -515,10 +519,6 @@ 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;