From patchwork Fri Mar 10 04:38:05 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kui-Feng Lee X-Patchwork-Id: 13168732 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53962C64EC4 for ; Fri, 10 Mar 2023 04:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229453AbjCJEi3 (ORCPT ); Thu, 9 Mar 2023 23:38:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229445AbjCJEi2 (ORCPT ); Thu, 9 Mar 2023 23:38:28 -0500 Received: from mx0b-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 58EFE2686B for ; Thu, 9 Mar 2023 20:38:24 -0800 (PST) Received: from pps.filterd (m0109332.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 32A2rOBj031898 for ; Thu, 9 Mar 2023 20:38:23 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=meta.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding : content-type; s=s2048-2021-q4; bh=Ae7at/yqRiwV0EFFbvRGyyoC6Duoovht9fBeNHPTYSc=; b=W+hJVqnQdAlJi5CqQy3liDmQNma9U67ZJqtMyzR/IijxiS1E6MXuugOuqmmeJgKaZv/w Aeja7Ot0GS3i0hQ92NE5f5lC6xH1QyakUevQJ/ZMtz70ZpyxM+LujTPffuKjKcFekuG2 kUk/QzhTr3rkxhc1/ttPzf3ikmrmEHhGsJooFYhEY1NpINTWFI9RUcgRQnJniF74BBHp Jf0Q7Pi/XxG8H8uPvqqy4eUlt8mw+c6QImq1ht/RGC7lqAOiA9S0yec0YedZJb4XDXwH ZTbCJEMWUrkNpH6GJJq5n1OSplD1izhyleBENwvsJ2c1u2cWrlpahqoH+pir+ATK4URQ gg== Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3p7cp3xhaw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 09 Mar 2023 20:38:23 -0800 Received: from twshared24004.14.frc2.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.17; Thu, 9 Mar 2023 20:38:22 -0800 Received: by devbig931.frc1.facebook.com (Postfix, from userid 460691) id 5F8096F6BD94; Thu, 9 Mar 2023 20:38:20 -0800 (PST) From: Kui-Feng Lee To: , , , , , , CC: Kui-Feng Lee Subject: [PATCH bpf-next v6 1/8] bpf: Retire the struct_ops map kvalue->refcnt. Date: Thu, 9 Mar 2023 20:38:05 -0800 Message-ID: <20230310043812.3087672-2-kuifeng@meta.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230310043812.3087672-1-kuifeng@meta.com> References: <20230310043812.3087672-1-kuifeng@meta.com> MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-GUID: nK0L9O5EpSJgYsRIz6KdiFaltH_hhgKR X-Proofpoint-ORIG-GUID: nK0L9O5EpSJgYsRIz6KdiFaltH_hhgKR X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-03-10_01,2023-03-09_01,2023-02-09_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net We have replaced kvalue-refcnt with synchronize_rcu() to wait for an RCU grace period. Maintenance of kvalue->refcnt was a complicated task, as we had to simultaneously keep track of two reference counts: one for the reference count of bpf_map. When the kvalue->refcnt reaches zero, we also have to reduce the reference count on bpf_map - yet these steps are not performed in an atomic manner and require us to be vigilant when managing them. By eliminating kvalue->refcnt, we can make our maintenance more straightforward as the refcount of bpf_map is now solely managed! To prevent the trampoline image of a struct_ops from being released while it is still in use, we wait for an RCU grace period. The setsockopt(TCP_CONGESTION, "...") command allows you to change your socket's congestion control algorithm and can result in releasing the old struct_ops implementation. Moreover, since this function is exposed through bpf_setsockopt(), it may be accessed by BPF programs as well. To ensure that the trampoline image belonging to struct_op can be safely called while its method is in use, struct_ops is safeguarded with rcu_read_lock(). Doing so prevents any destruction of the associated images before returning from a trampoline and requires us to wait for an RCU grace period. Signed-off-by: Kui-Feng Lee --- include/linux/bpf.h | 1 + kernel/bpf/bpf_struct_ops.c | 68 ++++++++++++++++++++----------------- kernel/bpf/syscall.c | 6 ++-- 3 files changed, 42 insertions(+), 33 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index e64ff1e89fb2..00ca92ea6f2e 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1938,6 +1938,7 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd); struct bpf_map *__bpf_map_get(struct fd f); void bpf_map_inc(struct bpf_map *map); void bpf_map_inc_with_uref(struct bpf_map *map); +struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref); struct bpf_map * __must_check bpf_map_inc_not_zero(struct bpf_map *map); void bpf_map_put_with_uref(struct bpf_map *map); void bpf_map_put(struct bpf_map *map); diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index 38903fb52f98..ab7811a4c1dd 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -58,6 +58,11 @@ struct bpf_struct_ops_map { struct bpf_struct_ops_value kvalue; }; +struct bpf_struct_ops_link { + struct bpf_link link; + struct bpf_map __rcu *map; +}; + #define VALUE_PREFIX "bpf_struct_ops_" #define VALUE_PREFIX_LEN (sizeof(VALUE_PREFIX) - 1) @@ -249,6 +254,7 @@ int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key, struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map; struct bpf_struct_ops_value *uvalue, *kvalue; enum bpf_struct_ops_state state; + s64 refcnt; if (unlikely(*(u32 *)key != 0)) return -ENOENT; @@ -267,7 +273,14 @@ int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key, uvalue = value; memcpy(uvalue, st_map->uvalue, map->value_size); uvalue->state = state; - refcount_set(&uvalue->refcnt, refcount_read(&kvalue->refcnt)); + + /* This value offers the user space a general estimate of how + * many sockets are still utilizing this struct_ops for TCP + * congestion control. The number might not be exact, but it + * should sufficiently meet our present goals. + */ + refcnt = atomic64_read(&map->refcnt) - atomic64_read(&map->usercnt); + refcount_set(&uvalue->refcnt, max_t(s64, refcnt, 0)); return 0; } @@ -491,7 +504,6 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key, *(unsigned long *)(udata + moff) = prog->aux->id; } - refcount_set(&kvalue->refcnt, 1); bpf_map_inc(map); set_memory_rox((long)st_map->image, 1); @@ -536,8 +548,7 @@ static int bpf_struct_ops_map_delete_elem(struct bpf_map *map, void *key) switch (prev_state) { case BPF_STRUCT_OPS_STATE_INUSE: st_map->st_ops->unreg(&st_map->kvalue.data); - if (refcount_dec_and_test(&st_map->kvalue.refcnt)) - bpf_map_put(map); + bpf_map_put(map); return 0; case BPF_STRUCT_OPS_STATE_TOBEFREE: return -EINPROGRESS; @@ -574,6 +585,19 @@ static void bpf_struct_ops_map_free(struct bpf_map *map) { struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map; + /* The struct_ops's function may switch to another struct_ops. + * + * For example, bpf_tcp_cc_x->init() may switch to + * another tcp_cc_y by calling + * setsockopt(TCP_CONGESTION, "tcp_cc_y"). + * During the switch, bpf_struct_ops_put(tcp_cc_x) is called + * and its refcount may reach 0 which then free its + * trampoline image while tcp_cc_x is still running. + * + * Thus, a rcu grace period is needed here. + */ + synchronize_rcu(); + if (st_map->links) bpf_struct_ops_map_put_progs(st_map); bpf_map_area_free(st_map->links); @@ -676,41 +700,23 @@ const struct bpf_map_ops bpf_struct_ops_map_ops = { bool bpf_struct_ops_get(const void *kdata) { struct bpf_struct_ops_value *kvalue; + struct bpf_struct_ops_map *st_map; + struct bpf_map *map; kvalue = container_of(kdata, struct bpf_struct_ops_value, data); + st_map = container_of(kvalue, struct bpf_struct_ops_map, kvalue); - return refcount_inc_not_zero(&kvalue->refcnt); -} - -static void bpf_struct_ops_put_rcu(struct rcu_head *head) -{ - struct bpf_struct_ops_map *st_map; - - st_map = container_of(head, struct bpf_struct_ops_map, rcu); - bpf_map_put(&st_map->map); + map = __bpf_map_inc_not_zero(&st_map->map, false); + return !IS_ERR(map); } void bpf_struct_ops_put(const void *kdata) { struct bpf_struct_ops_value *kvalue; + struct bpf_struct_ops_map *st_map; kvalue = container_of(kdata, struct bpf_struct_ops_value, data); - if (refcount_dec_and_test(&kvalue->refcnt)) { - struct bpf_struct_ops_map *st_map; - - st_map = container_of(kvalue, struct bpf_struct_ops_map, - kvalue); - /* The struct_ops's function may switch to another struct_ops. - * - * For example, bpf_tcp_cc_x->init() may switch to - * another tcp_cc_y by calling - * setsockopt(TCP_CONGESTION, "tcp_cc_y"). - * During the switch, bpf_struct_ops_put(tcp_cc_x) is called - * and its map->refcnt may reach 0 which then free its - * trampoline image while tcp_cc_x is still running. - * - * Thus, a rcu grace period is needed here. - */ - call_rcu(&st_map->rcu, bpf_struct_ops_put_rcu); - } + st_map = container_of(kvalue, struct bpf_struct_ops_map, kvalue); + + bpf_map_put(&st_map->map); } diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index f406dfa13792..ec03f9e450ad 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1287,8 +1287,10 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd) return map; } -/* map_idr_lock should have been held */ -static struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref) +/* map_idr_lock should have been held or the map should have been + * protected by rcu read lock. + */ +struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref) { int refold;