From bba1dc0b55ac462d24ed1228ad49800c238cd6d7 Mon Sep 17 00:00:00 2001
From: Alexei Starovoitov <ast@kernel.org>
Date: Mon, 29 Jun 2020 21:33:39 -0700
Subject: [PATCH] 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: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/bpf/20200630043343.53195-2-alexei.starovoitov@gmail.com
---
kernel/bpf/arraymap.c | 9 ---------
kernel/bpf/hashtab.c | 8 +++-----
kernel/bpf/lpm_trie.c | 5 -----
kernel/bpf/queue_stack_maps.c | 7 -------
kernel/bpf/reuseport_array.c | 2 --
kernel/bpf/ringbuf.c | 7 -------
kernel/bpf/stackmap.c | 3 ---
7 files changed, 3 insertions(+), 38 deletions(-)
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index ec5cd11032aa5..c66e8273fccda 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -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);
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index acd06081d81dc..d4378d7d442b9 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -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.
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index 1abd4e3f906de..44474bf3ab7ad 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -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.
diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c
index 80c66a6d7c548..44184f82916a9 100644
--- a/kernel/bpf/queue_stack_maps.c
+++ b/kernel/bpf/queue_stack_maps.c
@@ -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);
}
diff --git a/kernel/bpf/reuseport_array.c b/kernel/bpf/reuseport_array.c
index a09922f656e40..3625c4fcc65c3 100644
--- a/kernel/bpf/reuseport_array.c
+++ b/kernel/bpf/reuseport_array.c
@@ -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
diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index dbf37aff4827f..13a8d3967e074 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -215,13 +215,6 @@ static void ringbuf_map_free(struct bpf_map *map)
{
struct bpf_ringbuf_map *rb_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();
-
rb_map = container_of(map, struct bpf_ringbuf_map, map);
bpf_ringbuf_free(rb_map->rb);
kfree(rb_map);
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 27dc9b1b08a52..071f98d0f7c68 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -604,9 +604,6 @@ static void stack_map_free(struct bpf_map *map)
{
struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
- /* wait for bpf programs to complete before freeing stack map */
- synchronize_rcu();
-
bpf_map_area_free(smap->elems);
pcpu_freelist_destroy(&smap->freelist);
bpf_map_area_free(smap);
--
2.30.2