Messages in this thread | | | From | Yosry Ahmed <> | Date | Thu, 7 Dec 2023 09:52:54 -0800 | Subject | Re: [PATCH-cgroup v2] cgroup: Move rcu_head up near the top of cgroup_root |
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On Thu, Dec 7, 2023 at 5:46 AM Waiman Long <longman@redhat.com> wrote: > > 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 <sfr@canb.auug.org.au> > Closes: https://lore.kernel.org/lkml/20231207143806.114e0a74@canb.auug.org.au/ > Signed-off-by: Waiman Long <longman@redhat.com> > Acked-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
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