Previous patch adds 1:1 mapping between all 211 LSM hooks
and bpf_cgroup program array. Instead of reserving a slot per
possible hook, reserve 10 slots per cgroup for lsm programs.
Those slots are dynamically allocated on demand and reclaimed.

It should be possible to eventually extend this idea to all hooks if
the memory consumption is unacceptable and shrink overall effective
programs array.

struct cgroup_bpf {
	struct bpf_prog_array *    effective[33];        /*     0   264 */
	/* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */
	struct hlist_head          progs[33];            /*   264   264 */
	/* --- cacheline 8 boundary (512 bytes) was 16 bytes ago --- */
	u8                         flags[33];            /*   528    33 */

	/* XXX 7 bytes hole, try to pack */

	struct list_head           storages;             /*   568    16 */
	/* --- cacheline 9 boundary (576 bytes) was 8 bytes ago --- */
	struct bpf_prog_array *    inactive;             /*   584     8 */
	struct percpu_ref          refcnt;               /*   592    16 */
	struct work_struct         release_work;         /*   608    72 */

	/* size: 680, cachelines: 11, members: 7 */
	/* sum members: 673, holes: 1, sum holes: 7 */
	/* last cacheline: 40 bytes */
};

Signed-off-by: Stanislav Fomichev <redacted>
---
 include/linux/bpf-cgroup-defs.h |   3 +-
 include/linux/bpf_lsm.h         |   6 --
 kernel/bpf/bpf_lsm.c            |   5 --
 kernel/bpf/cgroup.c             | 107 +++++++++++++++++++++++++++-----
 4 files changed, 94 insertions(+), 27 deletions(-)

diff --git a/include/linux/bpf-cgroup-defs.h b/include/linux/bpf-cgroup-defs.h
index d5a70a35dace..359d3f16abea 100644
--- a/include/linux/bpf-cgroup-defs.h
+++ b/include/linux/bpf-cgroup-defs.h

@@ -10,7 +10,8 @@
 
 struct bpf_prog_array;
 
-#define CGROUP_LSM_NUM 211 /* will be addressed in the next patch */
+/* Maximum number of concurrently attachable per-cgroup LSM hooks. */
+#define CGROUP_LSM_NUM 10
 
 enum cgroup_bpf_attach_type {
 	CGROUP_BPF_ATTACH_TYPE_INVALID = -1,

diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index 7f0e59f5f9be..613de44aa429 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h

@@ -43,7 +43,6 @@ extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
 void bpf_inode_storage_free(struct inode *inode);
 
 int bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t *bpf_func);
-int bpf_lsm_hook_idx(u32 btf_id);
 
 #else /* !CONFIG_BPF_LSM */
 

@@ -74,11 +73,6 @@ static inline int bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
 	return -ENOENT;
 }
 
-static inline int bpf_lsm_hook_idx(u32 btf_id)
-{
-	return -EINVAL;
-}
-
 #endif /* CONFIG_BPF_LSM */
 
 #endif /* _LINUX_BPF_LSM_H */

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index a0e68ef5dfb1..1079c747e061 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c

@@ -91,11 +91,6 @@ int bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
 	return 0;
 }
 
-int bpf_lsm_hook_idx(u32 btf_id)
-{
-	return btf_id_set_index(&bpf_lsm_hooks, btf_id);
-}
-
 int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
 			const struct bpf_prog *prog)
 {

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 9cc38454e402..787ff6cf8d42 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c

@@ -79,10 +79,13 @@ unsigned int __cgroup_bpf_run_lsm_sock(const void *ctx,
 	shim_prog = (const struct bpf_prog *)((void *)insn - offsetof(struct bpf_prog, insnsi));
 
 	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
-	if (likely(cgrp))
+	if (likely(cgrp)) {
+		rcu_read_lock(); /* See bpf_lsm_attach_type_get(). */