bpf: Remove prealloc-only restriction for sleepable bpf programs.

Since hash map is now converted to bpf_mem_alloc and it's waiting for rcu and
rcu_tasks_trace GPs before freeing elements into global memory slabs it's safe
to use dynamically allocated hash maps in sleepable bpf programs.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220902211058.60789-15-alexei.starovoitov@gmail.com

kernel/bpf/verifier.c

@@ -12586,14 +12586,6 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
 	return err;
 }
 
-static int check_map_prealloc(struct bpf_map *map)
-{
-	return (map->map_type != BPF_MAP_TYPE_HASH &&
-		map->map_type != BPF_MAP_TYPE_PERCPU_HASH &&
-		map->map_type != BPF_MAP_TYPE_HASH_OF_MAPS) ||
-		!(map->map_flags & BPF_F_NO_PREALLOC);
-}
-
 static bool is_tracing_prog_type(enum bpf_prog_type type)
 {
 	switch (type) {
@@ -12608,15 +12600,6 @@ static bool is_tracing_prog_type(enum bpf_prog_type type)
 	}
 }
 
-static bool is_preallocated_map(struct bpf_map *map)
-{
-	if (!check_map_prealloc(map))
-		return false;
-	if (map->inner_map_meta && !check_map_prealloc(map->inner_map_meta))
-		return false;
-	return true;
-}
-
 static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 					struct bpf_map *map,
 					struct bpf_prog *prog)
@@ -12669,12 +12652,6 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 		case BPF_MAP_TYPE_LRU_PERCPU_HASH:
 		case BPF_MAP_TYPE_ARRAY_OF_MAPS:
 		case BPF_MAP_TYPE_HASH_OF_MAPS:
-			if (!is_preallocated_map(map)) {
-				verbose(env,
-					"Sleepable programs can only use preallocated maps\n");
-				return -EINVAL;
-			}
-			break;
 		case BPF_MAP_TYPE_RINGBUF:
 		case BPF_MAP_TYPE_INODE_STORAGE:
 		case BPF_MAP_TYPE_SK_STORAGE: