From patchwork Mon Mar 1 16:04:51 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 389656 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=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT 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 EBE4CC433E6 for ; Mon, 1 Mar 2021 18:36:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AC20064E45 for ; Mon, 1 Mar 2021 18:36:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240026AbhCASfT (ORCPT ); Mon, 1 Mar 2021 13:35:19 -0500 Received: from mail.kernel.org ([198.145.29.99]:43162 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240006AbhCAS2R (ORCPT ); Mon, 1 Mar 2021 13:28:17 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0F781650AD; Mon, 1 Mar 2021 17:39:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614620355; bh=W0oZqIwJv6gjpUQrHiC3w9wbrXYkCuhkY7788ApI77I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Aqi7vRB6RFWMLT5IgiXHvwoOP+pwcHcUnCGvIDPCcyF9E7yqwinmeMGPE0VDy9X/t PoNT51HvyCaM7ScggCCfMCPUyqZev1l3ZmPS8rN1Vv6mOgUNaxVOIPz9LbMOXxV/Qn 7gT1VlnCpF9QZEm/bRsUWczDcAM93I41WQ218Bx4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Dumazet , Arjun Roy , Wei Wang , "David S. Miller" , Sasha Levin Subject: [PATCH 5.11 123/775] tcp: fix SO_RCVLOWAT related hangs under mem pressure Date: Mon, 1 Mar 2021 17:04:51 +0100 Message-Id: <20210301161207.750462425@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161201.679371205@linuxfoundation.org> References: <20210301161201.679371205@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Eric Dumazet [ Upstream commit f969dc5a885736842c3511ecdea240fbb02d25d9 ] While commit 24adbc1676af ("tcp: fix SO_RCVLOWAT hangs with fat skbs") fixed an issue vs too small sk_rcvbuf for given sk_rcvlowat constraint, it missed to address issue caused by memory pressure. 1) If we are under memory pressure and socket receive queue is empty. First incoming packet is allowed to be queued, after commit 76dfa6082032 ("tcp: allow one skb to be received per socket under memory pressure") But we do not send EPOLLIN yet, in case tcp_data_ready() sees sk_rcvlowat is bigger than skb length. 2) Then, when next packet comes, it is dropped, and we directly call sk->sk_data_ready(). 3) If application is using poll(), tcp_poll() will then use tcp_stream_is_readable() and decide the socket receive queue is not yet filled, so nothing will happen. Even when sender retransmits packets, phases 2) & 3) repeat and flow is effectively frozen, until memory pressure is off. Fix is to consider tcp_under_memory_pressure() to take care of global memory pressure or memcg pressure. Fixes: 24adbc1676af ("tcp: fix SO_RCVLOWAT hangs with fat skbs") Signed-off-by: Eric Dumazet Reported-by: Arjun Roy Suggested-by: Wei Wang Reviewed-by: Wei Wang Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- include/net/tcp.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 25bbada379c46..244208f6f6c2a 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1431,8 +1431,13 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied); */ static inline bool tcp_rmem_pressure(const struct sock *sk) { - int rcvbuf = READ_ONCE(sk->sk_rcvbuf); - int threshold = rcvbuf - (rcvbuf >> 3); + int rcvbuf, threshold; + + if (tcp_under_memory_pressure(sk)) + return true; + + rcvbuf = READ_ONCE(sk->sk_rcvbuf); + threshold = rcvbuf - (rcvbuf >> 3); return atomic_read(&sk->sk_rmem_alloc) > threshold; }