[RFC PATCH bpf-next v6 10/12] mm/bpf: Add BPF_F_ALLOW_OVERRIDE support for memcg_bpf_ops
From: Hui Zhu <hidden>
Date: 2026-02-04 09:01:25
Also in:
bpf, cgroups, linux-kselftest, linux-mm, lkml
Subsystem:
bpf [memory management extensions], control group - memory resource controller (memcg), memory management, the rest · Maintainers:
Roman Gushchin, JP Kobryn, Shakeel Butt, Johannes Weiner, Michal Hocko, Andrew Morton, Linus Torvalds
From: Hui Zhu <redacted> To allow for more flexible attachment policies in nested cgroup hierarchies, this patch introduces support for the `BPF_F_ALLOW_OVERRIDE` flag for `memcg_bpf_ops`. When a `memcg_bpf_ops` is attached to a cgroup with this flag, it permits child cgroups to attach their own, different `memcg_bpf_ops`, overriding the parent's inherited program. Without this flag, attaching a BPF program to a cgroup that already has one (either directly or via inheritance) will fail. The implementation involves: - Adding a `bpf_ops_flags` field to `struct mem_cgroup`. - During registration (`bpf_memcg_ops_reg`), checking for existing programs and the `BPF_F_ALLOW_OVERRIDE` flag. - During unregistration (`bpf_memcg_ops_unreg`), correctly restoring the parent's BPF program to the cgroup hierarchy. - Ensuring flags are inherited by child cgroups during online events. This change enables complex, multi-level policy enforcement where different subtrees of the cgroup hierarchy can have distinct memory management BPF programs. Signed-off-by: Geliang Tang <geliang@kernel.org> Signed-off-by: Hui Zhu <redacted> --- include/linux/memcontrol.h | 1 + mm/bpf_memcontrol.c | 96 ++++++++++++++++++++++++++------------ 2 files changed, 66 insertions(+), 31 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d91dbb95069b..c7b32a01a854 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h@@ -355,6 +355,7 @@ struct mem_cgroup { #ifdef CONFIG_BPF_SYSCALL struct memcg_bpf_ops *bpf_ops; + u32 bpf_ops_flags; #endif struct mem_cgroup_per_node *nodeinfo[];
diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
index 72b720400628..909751263f98 100644
--- a/mm/bpf_memcontrol.c
+++ b/mm/bpf_memcontrol.c@@ -204,10 +204,11 @@ void memcontrol_bpf_online(struct mem_cgroup *memcg) /* * Because only functions bpf_memcg_ops_reg and bpf_memcg_ops_unreg - * write to memcg->bpf_ops under the protection of cgroup_mutex, - * ensuring that cgroup_mutex is already locked here allows safe - * reading and writing of memcg->bpf_ops without needing to acquire - * a lock on memcg_bpf_srcu. + * write to memcg->bpf_ops and memcg->bpf_ops_flags under the + * protection of cgroup_mutex, ensuring that cgroup_mutex is already + * locked here allows safe reading and writing of memcg->bpf_ops and + * memcg->bpf_ops_flags without needing to acquire a lock on + * memcg_bpf_srcu. */ lockdep_assert_held(&cgroup_mutex);
@@ -218,6 +219,7 @@ void memcontrol_bpf_online(struct mem_cgroup *memcg) if (!ops) return; WRITE_ONCE(memcg->bpf_ops, ops); + memcg->bpf_ops_flags = parent_memcg->bpf_ops_flags; /* * If the BPF program implements it, call the online handler to
@@ -239,7 +241,7 @@ void memcontrol_bpf_offline(struct mem_cgroup *memcg) { struct memcg_bpf_ops *ops; - /* Same with function memcontrol_bpf_online. */ + /* Same locking rules as memcontrol_bpf_online(). */ lockdep_assert_held(&cgroup_mutex); ops = READ_ONCE(memcg->bpf_ops);
@@ -335,48 +337,62 @@ static int bpf_memcg_ops_init_member(const struct btf_type *t, return 0; } -/** - * clean_memcg_bpf_ops - Clear BPF ops from a memory cgroup hierarchy - * @memcg: Root memory cgroup to start from - * @ops: The specific BPF ops to remove - * - * Walks the cgroup hierarchy and clears bpf_ops for any cgroup that - * matches @ops. - */ -static void clean_memcg_bpf_ops(struct mem_cgroup *memcg, - struct memcg_bpf_ops *ops) -{ - struct mem_cgroup *iter = NULL; - - while ((iter = mem_cgroup_iter(memcg, iter, NULL))) { - if (READ_ONCE(iter->bpf_ops) == ops) - WRITE_ONCE(iter->bpf_ops, NULL); - } -} - static int bpf_memcg_ops_reg(void *kdata, struct bpf_link *link) { struct bpf_struct_ops_link *ops_link = container_of(link, struct bpf_struct_ops_link, link); - struct memcg_bpf_ops *ops = kdata; - struct mem_cgroup *memcg, *iter = NULL; + struct memcg_bpf_ops *ops = kdata, *old_ops; + struct mem_cgroup *memcg, *iter; int err = 0; + if (ops_link->flags & ~BPF_F_ALLOW_OVERRIDE) { + pr_err("only BPF_F_ALLOW_OVERRIDE supported for struct_ops\n"); + return -EOPNOTSUPP; + } + memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id); if (IS_ERR(memcg)) return PTR_ERR(memcg); cgroup_lock(); + + /* + * Check if memcg has bpf_ops and whether it is inherited from + * parent. + * If inherited and BPF_F_ALLOW_OVERRIDE is set, allow override. + */ + old_ops = READ_ONCE(memcg->bpf_ops); + if (old_ops) { + struct mem_cgroup *parent_memcg = parent_mem_cgroup(memcg); + + if (!parent_memcg || + !(memcg->bpf_ops_flags & BPF_F_ALLOW_OVERRIDE) || + READ_ONCE(parent_memcg->bpf_ops) != old_ops) { + err = -EBUSY; + goto unlock_out; + } + } + + /* Check for incompatible bpf_ops in descendants. */ + iter = NULL; while ((iter = mem_cgroup_iter(memcg, iter, NULL))) { - if (READ_ONCE(iter->bpf_ops)) { + struct memcg_bpf_ops *iter_ops = READ_ONCE(iter->bpf_ops); + + if (iter_ops && iter_ops != old_ops) { + /* cannot override existing bpf_ops of sub-cgroup. */ mem_cgroup_iter_break(memcg, iter); err = -EBUSY; - break; + goto unlock_out; } + } + + iter = NULL; + while ((iter = mem_cgroup_iter(memcg, iter, NULL))) { WRITE_ONCE(iter->bpf_ops, ops); + iter->bpf_ops_flags = ops_link->flags; } - if (err) - clean_memcg_bpf_ops(memcg, ops); + +unlock_out: cgroup_unlock(); mem_cgroup_put(memcg);
@@ -390,13 +406,31 @@ static void bpf_memcg_ops_unreg(void *kdata, struct bpf_link *link) = container_of(link, struct bpf_struct_ops_link, link); struct memcg_bpf_ops *ops = kdata; struct mem_cgroup *memcg; + struct mem_cgroup *iter; + struct memcg_bpf_ops *parent_bpf_ops = NULL; + u32 parent_bpf_ops_flags = 0; memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id); if (IS_ERR_OR_NULL(memcg)) goto out; cgroup_lock(); - clean_memcg_bpf_ops(memcg, ops); + + /* Get the parent bpf_ops and bpf_ops_flags */ + iter = parent_mem_cgroup(memcg); + if (iter) { + parent_bpf_ops = READ_ONCE(iter->bpf_ops); + parent_bpf_ops_flags = iter->bpf_ops_flags; + } + + iter = NULL; + while ((iter = mem_cgroup_iter(memcg, iter, NULL))) { + if (READ_ONCE(iter->bpf_ops) == ops) { + WRITE_ONCE(iter->bpf_ops, parent_bpf_ops); + iter->bpf_ops_flags = parent_bpf_ops_flags; + } + } + cgroup_unlock(); mem_cgroup_put(memcg);
--
2.43.0