BPF programs can run in nmi context and may trigger memcg charged memory allocation in such context. Recently linux added support to nmi safe page allocation along with memcg charging of such allocations. However the kmalloc/slab support and corresponding memcg charging is still lacking, To provide nmi safe support for memcg charging for kmalloc/slab allocations, we need nmi safe memcg stats because for kernel memory charging and stats happen together. At the moment, memcg charging and memcg stats are nmi safe and the only thing which is not nmi safe is adding the cgroup to the per-cpu rstat update tree. i.e. css_rstat_updated() which this series is doing. This series made css_rstat_updated by using per-cpu lockless lists whose node in embedded in individual struct cgroup_subsys_state and the per-cpu head is placed in struct cgroup_subsys. For rstat users without cgroup_subsys, a global per-cpu lockless list head is created. The main challenge to use lockless in this scenario was the potential multiple inserters from the stacked context i.e. process, softirq, hardirq & nmi, potentially using the same per-cpu lockless node of a given cgroup_subsys_state. The normal lockless list does not protect against such scenario. The multiple stacked inserters using potentially same lockless node was resolved by making one of them succeed on reset the lockless node and the winner gets to insert the lockless node in the corresponding lockless list. The losers can assume the lockless list insertion will eventually succeed and continue their operation. Changelog since v2: - Add more clear explanation in cover letter and in the comment as suggested by Andrew, Michal & Tejun. - Use this_cpu_cmpxchg() instead of try_cmpxchg() as suggested by Tejun. - Remove the per-cpu ss locks as they are not needed anymore. Changelog since v1: - Based on Yosry's suggestion always use llist on the update side and create the update tree on flush side [v1] https://lore.kernel.org/cgroups/20250429061211.1295443-1-shakeel.butt@xxxxxxxxx/ Shakeel Butt (4): cgroup: support to enable nmi-safe css_rstat_updated cgroup: make css_rstat_updated nmi safe cgroup: remove per-cpu per-subsystem locks memcg: cgroup: call css_rstat_updated irrespective of in_nmi() include/linux/cgroup-defs.h | 11 +-- include/trace/events/cgroup.h | 47 ---------- kernel/cgroup/rstat.c | 169 +++++++++++++--------------------- mm/memcontrol.c | 10 +- 4 files changed, 74 insertions(+), 163 deletions(-) -- 2.47.1
