Commit bba1dc0b authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

bpf: Remove redundant synchronize_rcu. 



bpf_free_used_maps() or close(map_fd) will trigger map_free callback.
bpf_free_used_maps() is called after bpf prog is no longer executing:
bpf_prog_put->call_rcu->bpf_prog_free->bpf_free_used_maps.
Hence there is no need to call synchronize_rcu() to protect map elements.

Note that hash_of_maps and array_of_maps update/delete inner maps via
sys_bpf() that calls maybe_wait_bpf_programs() and synchronize_rcu().

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Acked-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/bpf/20200630043343.53195-2-alexei.starovoitov@gmail.com
parent 8c183110

kernel/bpf/arraymap.c

+0 −9
Original line number Diff line number Diff line
@@ -386,13 +386,6 @@ static void array_map_free(struct bpf_map *map) 
{

	struct bpf_array *array = container_of(map, struct bpf_array, map);



	/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,

	 * so the programs (can be more than one that used this map) were

	 * disconnected from events. Wait for outstanding programs to complete

	 * and free the array

	 */

	synchronize_rcu();



	if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY)

		bpf_array_free_percpu(array);
@@ -546,8 +539,6 @@ static void fd_array_map_free(struct bpf_map *map) 
	struct bpf_array *array = container_of(map, struct bpf_array, map);

	int i;



	synchronize_rcu();



	/* make sure it's empty */

	for (i = 0; i < array->map.max_entries; i++)

		BUG_ON(array->ptrs[i] != NULL);

kernel/bpf/hashtab.c

+3 −5
Original line number Diff line number Diff line
@@ -1290,12 +1290,10 @@ static void htab_map_free(struct bpf_map *map) 
{

	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);



	/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,

	 * so the programs (can be more than one that used this map) were

	 * disconnected from events. Wait for outstanding critical sections in

	 * these programs to complete

	/* bpf_free_used_maps() or close(map_fd) will trigger this map_free callback.

	 * bpf_free_used_maps() is called after bpf prog is no longer executing.

	 * There is no need to synchronize_rcu() here to protect map elements.

	 */

	synchronize_rcu();



	/* some of free_htab_elem() callbacks for elements of this map may

	 * not have executed. Wait for them.

kernel/bpf/lpm_trie.c

+0 −5
Original line number Diff line number Diff line
@@ -589,11 +589,6 @@ static void trie_free(struct bpf_map *map) 
	struct lpm_trie_node __rcu **slot;

	struct lpm_trie_node *node;



	/* Wait for outstanding programs to complete

	 * update/lookup/delete/get_next_key and free the trie.

	 */

	synchronize_rcu();



	/* Always start at the root and walk down to a node that has no

	 * children. Then free that node, nullify its reference in the parent

	 * and start over.

kernel/bpf/queue_stack_maps.c

+0 −7
Original line number Diff line number Diff line
@@ -101,13 +101,6 @@ static void queue_stack_map_free(struct bpf_map *map) 
{

	struct bpf_queue_stack *qs = bpf_queue_stack(map);



	/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,

	 * so the programs (can be more than one that used this map) were

	 * disconnected from events. Wait for outstanding critical sections in

	 * these programs to complete

	 */

	synchronize_rcu();



	bpf_map_area_free(qs);

}

kernel/bpf/reuseport_array.c

+0 −2
Original line number Diff line number Diff line
@@ -96,8 +96,6 @@ static void reuseport_array_free(struct bpf_map *map) 
	struct sock *sk;

	u32 i;



	synchronize_rcu();



	/*

	 * ops->map_*_elem() will not be able to access this

	 * array now. Hence, this function only races with

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