From 1987c7aa44fef4605db7dc86fea571b6a488df98 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Mon, 29 Jun 2020 21:33:39 -0700 Subject: [PATCH] UPSTREAM: 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(). Change-Id: Iac22753fc71080d3cee7931f11f8ab8a30fe96c0 Signed-off-by: Alexei Starovoitov Acked-by: Andrii Nakryiko Acked-by: Paul E. McKenney 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 ad127ee43039..ed8033a218e9 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -389,13 +389,6 @@ 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); @@ -549,8 +542,6 @@ 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 2756d7699f35..c37382097ba8 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -1329,12 +1329,10 @@ 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 ddb13e3b383d..784654e81de7 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -609,11 +609,6 @@ 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 c2c74414aba6..c554980d361a 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 a09922f656e4..3625c4fcc65c 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 d5db2905ddb6..002f8a5c9e51 100644 --- a/kernel/bpf/ringbuf.c +++ b/kernel/bpf/ringbuf.c @@ -213,13 +213,6 @@ 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 a0d07a184a99..d2980bd20da9 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -617,9 +617,6 @@ 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);