bpf: Use kmalloc_nolock() in local storage unconditionally

Simplify local storage and selem memory alloc/free paths by switching to
kmalloc_nolock unconditionally.

While it is okay to call bpf_obj_free_fields() immediately in
bpf_selem_free() when reuse_now == true, it is kept only in
bpf_selem_free_rcu() to simplify the code. This requires rcu_barrier()
to be called unconditionally in bpf_local_storage_map_free() since
bpf_obj_free_fields() may also be called from rcu callbacks.

In addition, remove the argument, smap, from bpf_selem_free() and rely
on SDATA(selem)->smap for bpf_obj_free_fields(). This requires
initializing SDATA(selem)->smap earlier during bpf_selem_alloc() as
bpf_local_storage_update() can allocate an selem and free it without
ever linking it to a map.

Finally, clean up and update comments. Note that, we already free selem
after an RCU grace period in bpf_local_storage_update() when
bpf_local_storage_alloc() failed the cmpxchg since commit c0d63f3
("bpf: Add bpf_selem_free()").

Signed-off-by: Amery Hung <[email protected]>

Author: ameryhung

include/linux/bpf_local_storage.h

@@ -53,9 +53,6 @@ struct bpf_local_storage_map {
 	u32 bucket_log;
 	u16 elem_size;
 	u16 cache_idx;
-	struct bpf_mem_alloc selem_ma;
-	struct bpf_mem_alloc storage_ma;
-	bool bpf_ma;
 };
 
 struct bpf_local_storage_data {
@@ -129,8 +126,7 @@ int bpf_local_storage_map_alloc_check(union bpf_attr *attr);
 
 struct bpf_map *
 bpf_local_storage_map_alloc(union bpf_attr *attr,
-			    struct bpf_local_storage_cache *cache,
-			    bool bpf_ma);
+			    struct bpf_local_storage_cache *cache);
 
 void __bpf_local_storage_insert_cache(struct bpf_local_storage *local_storage,
 				      struct bpf_local_storage_map *smap,
@@ -186,9 +182,7 @@ struct bpf_local_storage_elem *
 bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner, void *value,
 		bool swap_uptrs, gfp_t gfp_flags);
 
-void bpf_selem_free(struct bpf_local_storage_elem *selem,
-		    struct bpf_local_storage_map *smap,
-		    bool reuse_now);
+void bpf_selem_free(struct bpf_local_storage_elem *selem, bool reuse_now);
 
 int
 bpf_local_storage_alloc(void *owner,

kernel/bpf/bpf_cgrp_storage.c

@@ -146,7 +146,7 @@ static int notsupp_get_next_key(struct bpf_map *map, void *key, void *next_key)
 
 static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
 {
-	return bpf_local_storage_map_alloc(attr, &cgroup_cache, true);
+	return bpf_local_storage_map_alloc(attr, &cgroup_cache);
 }
 
 static void cgroup_storage_map_free(struct bpf_map *map)

kernel/bpf/bpf_inode_storage.c

@@ -181,7 +181,7 @@ static int notsupp_get_next_key(struct bpf_map *map, void *key,
 
 static struct bpf_map *inode_storage_map_alloc(union bpf_attr *attr)
 {
-	return bpf_local_storage_map_alloc(attr, &inode_cache, false);
+	return bpf_local_storage_map_alloc(attr, &inode_cache);
 }
 
 static void inode_storage_map_free(struct bpf_map *map)