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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76172C6FD1D for ; Fri, 7 Apr 2023 17:17:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230082AbjDGRRE (ORCPT ); Fri, 7 Apr 2023 13:17:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50458 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230035AbjDGRRD (ORCPT ); Fri, 7 Apr 2023 13:17:03 -0400 Received: from mail-pj1-x1036.google.com (mail-pj1-x1036.google.com [IPv6:2607:f8b0:4864:20::1036]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CE2CDAD13; Fri, 7 Apr 2023 10:17:02 -0700 (PDT) Received: by mail-pj1-x1036.google.com with SMTP id nh20-20020a17090b365400b0024496d637e1so4763572pjb.5; Fri, 07 Apr 2023 10:17:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680887822; x=1683479822; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=z1SkSwJ+B3plp80uNFxZv+C5LrwCVTyzF6SA03WoEAY=; b=K9C8F+SAKyVGDPOF4BTIE3N2qlEMEu080cA+t6WZs8TvkMzfD4kykJnh7a5argtB21 WV6VRtqXafU/G5hxtsdxJbkXVhZ4vSgEnkSR3nTbcaIAA7SAPy90d2Z0snGcToQNoLx+ HSHsXQz8gZuJTIXx6ek4fvr3mz5Zr93mrBWWh0iScKHJwAezoliFOKRrLTGvU9J7AJN0 er56sklWbIfeGseinSEjKaM8C/2X6B3CIuXiCoB9lPrdkrjfCch3LctFnm4BUCxuaOFv pnLBW2uZ9XiAvnxb45OjL44uV5vidIZ0Wfn1WONXo+U/yGaeC/PO8ssqScCf6vxjmzft Z02Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680887822; x=1683479822; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=z1SkSwJ+B3plp80uNFxZv+C5LrwCVTyzF6SA03WoEAY=; b=QXlm6DAHzp3Ksg6c1Rh+9Kig2kLW1w/fNJdfSXaSkgKrMd9Fn0l53vy+aCa9R+Eezr twQ0G610pKAo05nLqvAig1yfVTNZ1xUYPOO4lmU9kECP3feJUyKpaWYppawRlOHPSOH9 Mj45aBDHcKFrDnDaL8kmf60OtoPytiTzV6NCCpm5GblNYTlZ2htE9DGS5g5uvLN9rp4f yGDJZUhpJoVtTq1H6pcgRS/cZOR8BNpmmFt4tRHQeYZXg9VirS5csoWK1phtYBJwledk orajo6QIf4TvJGGgOdHg/jd1PscORQb08vs+2hednZBOJwb1EsRn3fx8YQtYxhlWyldR 9B4Q== X-Gm-Message-State: AAQBX9fchDMjXW8j3dc4rWjeZr9XGBFIWnVsojiCjC83SgsD5SKWfw79 ZgrosY+DTd+ohhuuuKgPlN0= X-Google-Smtp-Source: AKy350aLbUrwMecU0Sgu/hlDyAroALJbafNOiYIOxU0nk4/O+iboyfLESEPHvnS4ApbXl8TnM2Mv0A== X-Received: by 2002:a17:90b:1bc9:b0:23b:3b3a:54c2 with SMTP id oa9-20020a17090b1bc900b0023b3b3a54c2mr3041538pjb.48.1680887822314; Fri, 07 Apr 2023 10:17:02 -0700 (PDT) Received: from john.lan ([98.97.116.126]) by smtp.gmail.com with ESMTPSA id p1-20020a1709028a8100b0019b0937003esm3185425plo.150.2023.04.07.10.17.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Apr 2023 10:17:01 -0700 (PDT) From: John Fastabend To: jakub@cloudflare.com, daniel@iogearbox.net, lmb@isovalent.com, edumazet@google.com Cc: john.fastabend@gmail.com, bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org, andrii@kernel.org, will@isovalent.com Subject: [PATCH bpf v6 03/12] bpf: sockmap, improved check for empty queue Date: Fri, 7 Apr 2023 10:16:45 -0700 Message-Id: <20230407171654.107311-4-john.fastabend@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20230407171654.107311-1-john.fastabend@gmail.com> References: <20230407171654.107311-1-john.fastabend@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org We noticed some rare sk_buffs were stepping past the queue when system was under memory pressure. The general theory is to skip enqueueing sk_buffs when its not necessary which is the normal case with a system that is properly provisioned for the task, no memory pressure and enough cpu assigned. But, if we can't allocate memory due to an ENOMEM error when enqueueing the sk_buff into the sockmap receive queue we push it onto a delayed workqueue to retry later. When a new sk_buff is received we then check if that queue is empty. However, there is a problem with simply checking the queue length. When a sk_buff is being processed from the ingress queue but not yet on the sockmap msg receive queue its possible to also recv a sk_buff through normal path. It will check the ingress queue which is zero and then skip ahead of the pkt being processed. Previously we used sock lock from both contexts which made the problem harder to hit, but not impossible. To fix also check the 'state' variable where we would cache partially processed sk_buff. This catches the majority of cases. But, we also need to use the mutex lock around this check because we can't have both codes running and check sensibly. We could perhaps do this with atomic bit checks, but we are already here due to memory pressure so slowing things down a bit seems OK and simpler to just grab a lock. To reproduce issue we run NGINX compliance test with sockmap running and observe some flakes in our testing that we attributed to this issue. Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()") Tested-by: William Findlay Signed-off-by: John Fastabend --- net/core/skmsg.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 198bed303c51..f8731818b5c3 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -987,6 +987,7 @@ EXPORT_SYMBOL_GPL(sk_psock_tls_strp_read); static int sk_psock_verdict_apply(struct sk_psock *psock, struct sk_buff *skb, int verdict) { + struct sk_psock_work_state *state; struct sock *sk_other; int err = 0; u32 len, off; @@ -1003,13 +1004,28 @@ static int sk_psock_verdict_apply(struct sk_psock *psock, struct sk_buff *skb, skb_bpf_set_ingress(skb); + /* We need to grab mutex here because in-flight skb is in one of + * the following states: either on ingress_skb, in psock->state + * or being processed by backlog and neither in state->skb and + * ingress_skb may be also empty. The troublesome case is when + * the skb has been dequeued from ingress_skb list or taken from + * state->skb because we can not easily test this case. Maybe we + * could be clever with flags and resolve this but being clever + * got us here in the first place and we note this is done under + * sock lock and backlog conditions mean we are already running + * into ENOMEM or other performance hindering cases so lets do + * the obvious thing and grab the mutex. + */ + mutex_lock(&psock->work_mutex); + state = &psock->work_state; + /* If the queue is empty then we can submit directly * into the msg queue. If its not empty we have to * queue work otherwise we may get OOO data. Otherwise, * if sk_psock_skb_ingress errors will be handled by * retrying later from workqueue. */ - if (skb_queue_empty(&psock->ingress_skb)) { + if (skb_queue_empty(&psock->ingress_skb) && likely(!state->skb)) { len = skb->len; off = 0; if (skb_bpf_strparser(skb)) { @@ -1030,9 +1046,11 @@ static int sk_psock_verdict_apply(struct sk_psock *psock, struct sk_buff *skb, spin_unlock_bh(&psock->ingress_lock); if (err < 0) { skb_bpf_redirect_clear(skb); + mutex_unlock(&psock->work_mutex); goto out_free; } } + mutex_unlock(&psock->work_mutex); break; case __SK_REDIRECT: err = sk_psock_skb_redirect(psock, skb); -- 2.33.0