From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3D68C433DF for ; Tue, 30 Jun 2020 20:55:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A4542206C3 for ; Tue, 30 Jun 2020 20:55:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593550525; bh=8/jfzl09QncvCdMs7Y7cl0VwPtLXwxjLIFP2mihj2kM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=nBj+qiVsV5vC5Hx37dkw3f1AhbXmKTCCWqIAF2bX/8fK1iQQwf7CWcYtxFdK695Ce AFi4wVx8C6Av7UmrWjb2ySk3OifCsTEavZ7Mj3GUJB/BthgL0HAJjWGnev3hgeUekO DlXx7IqTkTmcSv3us/UlqrfoToXX/Yqj9eM/y1lU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726268AbgF3UzZ (ORCPT ); Tue, 30 Jun 2020 16:55:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:34570 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726097AbgF3UzZ (ORCPT ); Tue, 30 Jun 2020 16:55:25 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CFE49206C0; Tue, 30 Jun 2020 20:55:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593550523; bh=8/jfzl09QncvCdMs7Y7cl0VwPtLXwxjLIFP2mihj2kM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=i+u9BBRpzJ4mw+mQCTJHn6sDG4S9opjeqrd7nDBKby95kKy9q/nBd51wzOERXCV3a Em9A/pdsu7B7iBubS611V11b+hnoXxjzp00oHZ/Pk7vG7c16kVGXmuyYCZgpIvJ4Sh zYSvrg8cnrxjG9Wj63zc8/SXvHEkYqULeFHl3hbo= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id B0AE43522640; Tue, 30 Jun 2020 13:55:23 -0700 (PDT) Date: Tue, 30 Jun 2020 13:55:23 -0700 From: "Paul E. McKenney" To: Alexei Starovoitov Cc: davem@davemloft.net, daniel@iogearbox.net, netdev@vger.kernel.org, bpf@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v5 bpf-next 1/5] bpf: Remove redundant synchronize_rcu. Message-ID: <20200630205523.GJ9247@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200630043343.53195-1-alexei.starovoitov@gmail.com> <20200630043343.53195-2-alexei.starovoitov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200630043343.53195-2-alexei.starovoitov@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Jun 29, 2020 at 09:33:39PM -0700, Alexei Starovoitov wrote: > From: Alexei Starovoitov > > 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 > Acked-by: Andrii Nakryiko >From an RCU perspective: Acked-by: Paul E. McKenney > --- > 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 ec5cd11032aa..c66e8273fccd 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 acd06081d81d..d4378d7d442b 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 1abd4e3f906d..44474bf3ab7a 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 80c66a6d7c54..44184f82916a 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 dbf37aff4827..13a8d3967e07 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 27dc9b1b08a5..071f98d0f7c6 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); > -- > 2.23.0 >