bpf: Generalize caching for sk_storage.

Provide the a ability to define local storage caches on a per-object
type basis. The caches and caching indices for different objects should
not be inter-mixed as suggested in:

  https://lore.kernel.org/bpf/20200630193441.kdwnkestulg5erii@kafai-mbp.dhcp.thefacebook.com/

  "Caching a sk-storage at idx=0 of a sk should not stop an
  inode-storage to be cached at the same idx of a inode."
Signed-off-by: NKP Singh <kpsingh@google.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200825182919.1118197-3-kpsingh@chromium.org

include/net/bpf_sk_storage.h

@@ -3,6 +3,9 @@
 #ifndef _BPF_SK_STORAGE_H
 #define _BPF_SK_STORAGE_H
 
+#include <linux/types.h>
+#include <linux/spinlock.h>
+
 struct sock;
 
 void bpf_sk_storage_free(struct sock *sk);
@@ -15,6 +18,22 @@ struct sk_buff;
 struct nlattr;
 struct sock;
 
+#define BPF_LOCAL_STORAGE_CACHE_SIZE	16
+
+struct bpf_local_storage_cache {
+	spinlock_t idx_lock;
+	u64 idx_usage_counts[BPF_LOCAL_STORAGE_CACHE_SIZE];
+};
+
+#define DEFINE_BPF_STORAGE_CACHE(name)				\
+static struct bpf_local_storage_cache name = {			\
+	.idx_lock = __SPIN_LOCK_UNLOCKED(name.idx_lock),	\
+}
+
+u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache);
+void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
+				      u16 idx);
+
 #ifdef CONFIG_BPF_SYSCALL
 int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk);
 struct bpf_sk_storage_diag *

net/core/bpf_sk_storage.c

@@ -14,6 +14,8 @@
 
 #define BPF_LOCAL_STORAGE_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_CLONE)
 
+DEFINE_BPF_STORAGE_CACHE(sk_cache);
+
 struct bpf_local_storage_map_bucket {
 	struct hlist_head list;
 	raw_spinlock_t lock;
@@ -78,10 +80,6 @@ struct bpf_local_storage_elem {
 #define SELEM(_SDATA)							\
 	container_of((_SDATA), struct bpf_local_storage_elem, sdata)
 #define SDATA(_SELEM) (&(_SELEM)->sdata)
-#define BPF_LOCAL_STORAGE_CACHE_SIZE	16
-
-static DEFINE_SPINLOCK(cache_idx_lock);
-static u64 cache_idx_usage_counts[BPF_LOCAL_STORAGE_CACHE_SIZE];
 
 struct bpf_local_storage {
 	struct bpf_local_storage_data __rcu *cache[BPF_LOCAL_STORAGE_CACHE_SIZE];
@@ -521,16 +519,16 @@ static int sk_storage_delete(struct sock *sk, struct bpf_map *map)
 	return 0;
 }
 
-static u16 cache_idx_get(void)
+u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
 {
 	u64 min_usage = U64_MAX;
 	u16 i, res = 0;
 
-	spin_lock(&cache_idx_lock);
+	spin_lock(&cache->idx_lock);
 
 	for (i = 0; i < BPF_LOCAL_STORAGE_CACHE_SIZE; i++) {
-		if (cache_idx_usage_counts[i] < min_usage) {
-			min_usage = cache_idx_usage_counts[i];
+		if (cache->idx_usage_counts[i] < min_usage) {
+			min_usage = cache->idx_usage_counts[i];
 			res = i;
 
 			/* Found a free cache_idx */
@@ -538,18 +536,19 @@ static u16 cache_idx_get(void)
 				break;
 		}
 	}
-	cache_idx_usage_counts[res]++;
+	cache->idx_usage_counts[res]++;
 
-	spin_unlock(&cache_idx_lock);
+	spin_unlock(&cache->idx_lock);
 
 	return res;
 }
 
-static void cache_idx_free(u16 idx)
+void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
+				      u16 idx)
 {
-	spin_lock(&cache_idx_lock);
-	cache_idx_usage_counts[idx]--;
-	spin_unlock(&cache_idx_lock);
+	spin_lock(&cache->idx_lock);
+	cache->idx_usage_counts[idx]--;
+	spin_unlock(&cache->idx_lock);
 }
 
 /* Called by __sk_destruct() & bpf_sk_storage_clone() */
@@ -601,7 +600,7 @@ static void bpf_local_storage_map_free(struct bpf_map *map)
 
 	smap = (struct bpf_local_storage_map *)map;
 
-	cache_idx_free(smap->cache_idx);
+	bpf_local_storage_cache_idx_free(&sk_cache, smap->cache_idx);
 
 	/* Note that this map might be concurrently cloned from
 	 * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
@@ -718,7 +717,7 @@ static struct bpf_map *bpf_local_storage_map_alloc(union bpf_attr *attr)
 
 	smap->elem_size =
 		sizeof(struct bpf_local_storage_elem) + attr->value_size;
-	smap->cache_idx = cache_idx_get();
+	smap->cache_idx = bpf_local_storage_cache_idx_get(&sk_cache);
 
 	return &smap->map;
 }