bpf: Refactor some inode/task/sk storage functions for reuse

Refactor codes so that inode/task/sk storage implementation
can maximally share the same code. I also added some comments
in new function bpf_local_storage_unlink_nolock() to make
codes easy to understand. There is no functionality change.

Acked-by: David Vernet <void@manifault.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221026042845.672944-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 121 insertions, 69 deletions

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index 781d14167140..93d9b1b17bc8 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -113,9 +113,9 @@ static void bpf_selem_free_rcu(struct rcu_head *rcu)
  * The caller must ensure selem->smap is still valid to be
  * dereferenced for its smap->elem_size and smap->cache_idx.
  */
-bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
-				     struct bpf_local_storage_elem *selem,
-				     bool uncharge_mem, bool use_trace_rcu)
+static bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
+					    struct bpf_local_storage_elem *selem,
+					    bool uncharge_mem, bool use_trace_rcu)
 {
 	struct bpf_local_storage_map *smap;
 	bool free_local_storage;
@@ -501,7 +501,7 @@ unlock_err:
 	return ERR_PTR(err);
 }
 
-u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
+static u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
 {
 	u64 min_usage = U64_MAX;
 	u16 i, res = 0;
@@ -525,76 +525,14 @@ u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
 	return res;
 }
 
-void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
-				      u16 idx)
+static 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);
 }
 
-void bpf_local_storage_map_free(struct bpf_local_storage_map *smap,
-				int __percpu *busy_counter)
-{
-	struct bpf_local_storage_elem *selem;
-	struct bpf_local_storage_map_bucket *b;
-	unsigned int i;
-
-	/* Note that this map might be concurrently cloned from
-	 * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
-	 * RCU read section to finish before proceeding. New RCU
-	 * read sections should be prevented via bpf_map_inc_not_zero.
-	 */
-	synchronize_rcu();
-
-	/* bpf prog and the userspace can no longer access this map
-	 * now.  No new selem (of this map) can be added
-	 * to the owner->storage or to the map bucket's list.
-	 *
-	 * The elem of this map can be cleaned up here
-	 * or when the storage is freed e.g.
-	 * by bpf_sk_storage_free() during __sk_destruct().
-	 */
-	for (i = 0; i < (1U << smap->bucket_log); i++) {
-		b = &smap->buckets[i];
-
-		rcu_read_lock();
-		/* No one is adding to b->list now */
-		while ((selem = hlist_entry_safe(
-				rcu_dereference_raw(hlist_first_rcu(&b->list)),
-				struct bpf_local_storage_elem, map_node))) {
-			if (busy_counter) {
-				migrate_disable();
-				this_cpu_inc(*busy_counter);
-			}
-			bpf_selem_unlink(selem, false);
-			if (busy_counter) {
-				this_cpu_dec(*busy_counter);
-				migrate_enable();
-			}
-			cond_resched_rcu();
-		}
-		rcu_read_unlock();
-	}
-
-	/* While freeing the storage we may still need to access the map.
-	 *
-	 * e.g. when bpf_sk_storage_free() has unlinked selem from the map
-	 * which then made the above while((selem = ...)) loop
-	 * exit immediately.
-	 *
-	 * However, while freeing the storage one still needs to access the
-	 * smap->elem_size to do the uncharging in
-	 * bpf_selem_unlink_storage_nolock().
-	 *
-	 * Hence, wait another rcu grace period for the storage to be freed.
-	 */
-	synchronize_rcu();
-
-	kvfree(smap->buckets);
-	bpf_map_area_free(smap);
-}
-
 int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
 {
 	if (attr->map_flags & ~BPF_LOCAL_STORAGE_CREATE_FLAG_MASK ||
@@ -614,7 +552,7 @@ int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
 	return 0;
 }
 
-struct bpf_local_storage_map *bpf_local_storage_map_alloc(union bpf_attr *attr)
+static struct bpf_local_storage_map *__bpf_local_storage_map_alloc(union bpf_attr *attr)
 {
 	struct bpf_local_storage_map *smap;
 	unsigned int i;
@@ -664,3 +602,117 @@ int bpf_local_storage_map_check_btf(const struct bpf_map *map,
 
 	return 0;
 }
+
+bool bpf_local_storage_unlink_nolock(struct bpf_local_storage *local_storage)
+{
+	struct bpf_local_storage_elem *selem;
+	bool free_storage = false;
+	struct hlist_node *n;
+
+	/* Neither the bpf_prog nor the bpf_map's syscall
+	 * could be modifying the local_storage->list now.
+	 * Thus, no elem can be added to or deleted from the
+	 * local_storage->list by the bpf_prog or by the bpf_map's syscall.
+	 *
+	 * It is racing with bpf_local_storage_map_free() alone
+	 * when unlinking elem from the local_storage->list and
+	 * the map's bucket->list.
+	 */
+	hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
+		/* Always unlink from map before unlinking from
+		 * local_storage.
+		 */
+		bpf_selem_unlink_map(selem);
+		/* If local_storage list has only one element, the
+		 * bpf_selem_unlink_storage_nolock() will return true.
+		 * Otherwise, it will return false. The current loop iteration
+		 * intends to remove all local storage. So the last iteration
+		 * of the loop will set the free_cgroup_storage to true.
+		 */
+		free_storage = bpf_selem_unlink_storage_nolock(
+			local_storage, selem, false, false);
+	}
+
+	return free_storage;
+}
+
+struct bpf_map *
+bpf_local_storage_map_alloc(union bpf_attr *attr,
+			    struct bpf_local_storage_cache *cache)
+{
+	struct bpf_local_storage_map *smap;
+
+	smap = __bpf_local_storage_map_alloc(attr);
+	if (IS_ERR(smap))
+		return ERR_CAST(smap);
+
+	smap->cache_idx = bpf_local_storage_cache_idx_get(cache);
+	return &smap->map;
+}
+
+void bpf_local_storage_map_free(struct bpf_map *map,
+				struct bpf_local_storage_cache *cache,
+				int __percpu *busy_counter)
+{
+	struct bpf_local_storage_map_bucket *b;
+	struct bpf_local_storage_elem *selem;
+	struct bpf_local_storage_map *smap;
+	unsigned int i;
+
+	smap = (struct bpf_local_storage_map *)map;
+	bpf_local_storage_cache_idx_free(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
+	 * RCU read section to finish before proceeding. New RCU
+	 * read sections should be prevented via bpf_map_inc_not_zero.
+	 */
+	synchronize_rcu();
+
+	/* bpf prog and the userspace can no longer access this map
+	 * now.  No new selem (of this map) can be added
+	 * to the owner->storage or to the map bucket's list.
+	 *
+	 * The elem of this map can be cleaned up here
+	 * or when the storage is freed e.g.
+	 * by bpf_sk_storage_free() during __sk_destruct().
+	 */
+	for (i = 0; i < (1U << smap->bucket_log); i++) {
+		b = &smap->buckets[i];
+
+		rcu_read_lock();
+		/* No one is adding to b->list now */
+		while ((selem = hlist_entry_safe(
+				rcu_dereference_raw(hlist_first_rcu(&b->list)),
+				struct bpf_local_storage_elem, map_node))) {
+			if (busy_counter) {
+				migrate_disable();
+				this_cpu_inc(*busy_counter);
+			}
+			bpf_selem_unlink(selem, false);
+			if (busy_counter) {
+				this_cpu_dec(*busy_counter);
+				migrate_enable();
+			}
+			cond_resched_rcu();
+		}
+		rcu_read_unlock();
+	}
+
+	/* While freeing the storage we may still need to access the map.
+	 *
+	 * e.g. when bpf_sk_storage_free() has unlinked selem from the map
+	 * which then made the above while((selem = ...)) loop
+	 * exit immediately.
+	 *
+	 * However, while freeing the storage one still needs to access the
+	 * smap->elem_size to do the uncharging in
+	 * bpf_selem_unlink_storage_nolock().
+	 *
+	 * Hence, wait another rcu grace period for the storage to be freed.
+	 */
+	synchronize_rcu();
+
+	kvfree(smap->buckets);
+	bpf_map_area_free(smap);
+}