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[144.49.247.21]) by smtp-relay.gmail.com with ESMTPS id 6a1803df08f44-8b53ba0e66csm9616606d6.22.2026.05.04.07.53.44 for (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 04 May 2026 07:53:44 -0700 (PDT) X-Relaying-Domain: broadcom.com X-CFilter-Loop: Reflected Received: by mail-qk1-f199.google.com with SMTP id af79cd13be357-8eab2831ba2so62883585a.3 for ; Mon, 04 May 2026 07:53:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; t=1777906424; x=1778511224; darn=vger.kernel.org; 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=SHhLI5sBgOBTw5yVBP3uB++yW6cjDecz6JHS4uWuFPI=; b=Rg/p3AiBf4F0D4wlxPjxvo1QRvQUHLIhGKLb7wW/pExYm8FMLGdR/Ap5a0UndJDecG WAy+J8WIniQGRf58xAPasCupeu0YdULlBb8vhQUmIhWyAyN45X47eil6Ptldo0axNucK ykZoIcdHxbqVdHvzI+9mz+1lo10K5Z55mKwi8= X-Forwarded-Encrypted: i=1; AFNElJ/knGK25WiyyNrojU4ONLCd3Fy3bicovP9neH++QRVCxRkuVhTvBzparPREqUCus/bo4SWl6+02UyPycDw=@vger.kernel.org X-Received: by 2002:a05:620a:4154:b0:8d7:3f45:b95c with SMTP id af79cd13be357-8fd155f14camr1002870085a.2.1777906423660; Mon, 04 May 2026 07:53:43 -0700 (PDT) X-Received: by 2002:a05:620a:4154:b0:8d7:3f45:b95c with SMTP id af79cd13be357-8fd155f14camr1002864185a.2.1777906422882; Mon, 04 May 2026 07:53:42 -0700 (PDT) Received: from photon-d7fac424c0d3 ([192.19.161.250]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8fc2c91fb3bsm1046315985a.41.2026.05.04.07.53.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 May 2026 07:53:42 -0700 (PDT) From: Ankit Jain To: edumazet@google.com, kuba@kernel.org, netdev@vger.kernel.org Cc: davem@davemloft.net, pabeni@redhat.com, ncardwell@google.com, kuniyu@google.com, horms@kernel.org, shuah@kernel.org, quic_subashab@quicinc.com, quic_stranche@quicinc.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, karen.badiryan@broadcom.com, ajay.kaher@broadcom.com, alexey.makhalov@broadcom.com, vamsi-krishna.brahmajosyula@broadcom.com, yin.ding@broadcom.com, tapas.kundu@broadcom.com, Ankit Jain Subject: [PATCH net v2 1/2] tcp: protect locked SO_RCVBUF from Silly Window Syndrome Date: Mon, 4 May 2026 14:49:44 +0000 Message-ID: <20260504144945.13477-2-ankit-aj.jain@broadcom.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260504144945.13477-1-ankit-aj.jain@broadcom.com> References: <20260504144945.13477-1-ankit-aj.jain@broadcom.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-DetectorID-Processed: b00c1d49-9d2e-4205-b15f-d015386d3d5e When an application locks SO_RCVBUF, it expects strict memory bounds and disables TCP window auto-tuning. However, recent TCP memory fragmentation optimizations still apply dynamic truesize penalties to the `scaling_ratio` of these locked sockets. For workloads processing small, fragmented packets (like Java's Tomcat), this penalty drops the scaling_ratio to 1. This shrinks the dynamically calculated advertised window, leading to Silly Window Syndrome (SWS) deadlocks and 504 Gateway Timeouts. This patch fixes the issue by bypassing the truesize penalty for sockets with `SOCK_RCVBUF_LOCK` set. To ensure the kernel still defends against memory exhaustion from large aggregate payloads (e.g., GRO), the penalty is still applied if `skb->len` exceeds the advertised MSS. Fixes: a2cbb1603943 ("tcp: Update window clamping condition") Reported-by: Karen Badiryan Signed-off-by: Ankit Jain --- net/ipv4/tcp_input.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index d5c9e65d9760..569299dafa88 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -240,8 +240,14 @@ static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) /* Note: divides are still a bit expensive. * For the moment, only adjust scaling_ratio * when we update icsk_ack.rcv_mss. + * + * Protect locked SO_RCVBUF from Silly Window Syndrome + * due to truesize penalties on small packets. Allow + * penalty if aggregate payload (e.g., GRO) exceeds MSS. */ - if (unlikely(len != icsk->icsk_ack.rcv_mss)) { + if (unlikely(len != icsk->icsk_ack.rcv_mss && + (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK) || + skb->len > tcp_sk(sk)->advmss))) { u64 val = (u64)skb->len << TCP_RMEM_TO_WIN_SCALE; u8 old_ratio = tcp_sk(sk)->scaling_ratio; -- 2.53.0