From: Hui Zhu <[email protected]> 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 <[email protected]> Signed-off-by: Hui Zhu <[email protected]> --- include/linux/memcontrol.h | 1 + mm/bpf_memcontrol.c | 83 ++++++++++++++++++++++++-------------- 2 files changed, 53 insertions(+), 31 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 1083be5d0362..6e15da44ba35 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -354,6 +354,7 @@ 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 20c5c3552ce3..756a7d4eb4e3 100644 --- a/mm/bpf_memcontrol.c +++ b/mm/bpf_memcontrol.c @@ -213,6 +213,7 @@ void memcontrol_bpf_online(struct mem_cgroup *memcg) goto out; 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 @@ -340,52 +341,54 @@ static int bpf_memcg_ops_init_member(const struct btf_type *t, return 0; } -/** - * clean_memcg_bpf_ops - Detach BPF programs from a cgroup hierarchy. - * @memcg: The root of the cgroup hierarchy to clean. - * @ops: The specific ops struct to detach. If NULL, detach any ops. - * - * Iterates through all descendant cgroups of @memcg (including itself) - * and clears their bpf_ops pointer. This is used when a BPF program - * is detached or if attachment fails midway. - */ -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 (ops) { - if (!WARN_ON(READ_ONCE(iter->bpf_ops) != ops)) - WRITE_ONCE(iter->bpf_ops, NULL); - } else - 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 memcg_bpf_ops *ops = kdata, *parent_ops = NULL; struct mem_cgroup *memcg, *iter = NULL; int err = 0; + if (ops_link->flags & ~BPF_F_ALLOW_OVERRIDE) { + pr_err("attach only support BPF_F_ALLOW_OVERRIDE\n"); + return -EOPNOTSUPP; + } + memcg = mem_cgroup_get_from_ino(ops_link->cgroup_id); if (IS_ERR_OR_NULL(memcg)) return PTR_ERR(memcg); cgroup_lock(); - while ((iter = mem_cgroup_iter(memcg, iter, NULL))) { - if (READ_ONCE(iter->bpf_ops)) { - mem_cgroup_iter_break(memcg, iter); + + if (READ_ONCE(memcg->bpf_ops)) { + /* Check if bpf_ops of the parent is BPF_F_ALLOW_OVERRIDE. */ + if (memcg->bpf_ops_flags & BPF_F_ALLOW_OVERRIDE) { + iter = parent_mem_cgroup(memcg); + if (!iter || READ_ONCE(iter->bpf_ops) != + READ_ONCE(memcg->bpf_ops)) + goto busy_out; + + parent_ops = READ_ONCE(memcg->bpf_ops); + } else { +busy_out: err = -EBUSY; - break; + goto unlock_out; + } + } + + iter = NULL; + while ((iter = mem_cgroup_iter(memcg, iter, NULL))) { + struct memcg_bpf_ops *iter_ops = READ_ONCE(iter->bpf_ops); + + if (iter_ops && iter_ops != parent_ops) { + /* cannot override existing bpf_ops of sub-cgroup. */ + continue; } WRITE_ONCE(iter->bpf_ops, ops); + iter->bpf_ops_flags = ops_link->flags; } - if (err) - clean_memcg_bpf_ops(memcg, NULL); + +unlock_out: cgroup_unlock(); mem_cgroup_put(memcg); @@ -399,13 +402,31 @@ 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
