From patchwork Tue Mar 21 23:28:06 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: 13183381 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 65B5CC761A6 for ; Tue, 21 Mar 2023 23:28:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229648AbjCUX2g (ORCPT ); Tue, 21 Mar 2023 19:28:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43976 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229762AbjCUX2e (ORCPT ); Tue, 21 Mar 2023 19:28:34 -0400 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 602382686 for ; Tue, 21 Mar 2023 16:28:33 -0700 (PDT) Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 32LNGJLh011076 for ; Tue, 21 Mar 2023 16:28:33 -0700 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=yCIuXsuNrCBmzuSiAZsGrmHGqerpaTnqPUs3YtArSl4=; b=BCl/oJgnVrlLGnmbpVxi0X6qD2AmFb45oimHjGy3dfz4ZkGYE7/EVPshKK4tieldMACo 4ts+GSZf4pZ72WqN7ke4qpVqTDjJMnZzgcGvE1TPMIlYAzBXTmPPLxgurQpGT6Ge4svT Crw9zueGLdMt6yTdyDqwuceDcWz72X6gMgTyqfNFZytirlo779Ndl7fd8BsW5Lse+uP9 QxaweRtpM+6BVDrTWl3bJZU2unZOOUTtt0YB5UyUZgoqTnIVaXccTRwAownSFFTL9LDT 0jV5bGRb1J8XNOpg1HaM4alCZ9yaS11WECgnBtc1m+c+avN37KVd4diQeQ20KBnU1XAF Kg== Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3pfea0umv9-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 21 Mar 2023 16:28:32 -0700 Received: from ash-exhub204.TheFacebook.com (2620:10d:c0a8:83::4) by ash-exhub202.TheFacebook.com (2620:10d:c0a8:83::6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.17; Tue, 21 Mar 2023 16:28:29 -0700 Received: from twshared52565.14.frc2.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.17; Tue, 21 Mar 2023 16:28:29 -0700 Received: by devbig931.frc1.facebook.com (Postfix, from userid 460691) id 4F35C7EEB55A; Tue, 21 Mar 2023 16:28:15 -0700 (PDT) From: Kui-Feng Lee To: , , , , , , CC: Kui-Feng Lee Subject: [PATCH bpf-next v10 1/8] bpf: Retire the struct_ops map kvalue->refcnt. Date: Tue, 21 Mar 2023 16:28:06 -0700 Message-ID: <20230321232813.3376064-2-kuifeng@meta.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230321232813.3376064-1-kuifeng@meta.com> References: <20230321232813.3376064-1-kuifeng@meta.com> MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-GUID: 75lLbDKuDoCpP6FuKlC9hBBaLbmhdW70 X-Proofpoint-ORIG-GUID: 75lLbDKuDoCpP6FuKlC9hBBaLbmhdW70 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=2023-03-21_11,2023-03-21_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. It is fine. However, 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, the trampoline safeguarde the BPF program 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 | 73 ++++++++++++++++++++----------------- kernel/bpf/syscall.c | 6 ++- 3 files changed, 45 insertions(+), 35 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 3ef98fb92987..3304c84fe021 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1945,6 +1945,7 @@ 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..ca87258b42e9 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -11,6 +11,7 @@ #include #include #include +#include enum bpf_struct_ops_state { BPF_STRUCT_OPS_STATE_INIT, @@ -249,6 +250,7 @@ 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 +269,14 @@ 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 +500,6 @@ 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 +544,7 @@ 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; @@ -570,7 +577,7 @@ static void bpf_struct_ops_map_seq_show_elem(struct bpf_map *map, void *key, kfree(value); } -static void bpf_struct_ops_map_free(struct bpf_map *map) +static void __bpf_struct_ops_map_free(struct bpf_map *map) { struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map; @@ -582,6 +589,24 @@ static void bpf_struct_ops_map_free(struct bpf_map *map) bpf_map_area_free(st_map); } +static void bpf_struct_ops_map_free(struct bpf_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_mult(call_rcu, call_rcu_tasks); + + __bpf_struct_ops_map_free(map); +} + static int bpf_struct_ops_map_alloc_check(union bpf_attr *attr) { if (attr->key_size != sizeof(unsigned int) || attr->max_entries != 1 || @@ -630,7 +655,7 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr) NUMA_NO_NODE); st_map->image = bpf_jit_alloc_exec(PAGE_SIZE); if (!st_map->uvalue || !st_map->links || !st_map->image) { - bpf_struct_ops_map_free(map); + __bpf_struct_ops_map_free(map); return ERR_PTR(-ENOMEM); } @@ -676,41 +701,23 @@ 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 099e9068bcdd..cff0348a2871 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1303,8 +1303,10 @@ 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;