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[133.18.180.162]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b5031b98e5sm16550060c88.14.2026.11.14.04.42.11 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 14 Nov 2026 04:42:16 -0800 (PST) Content-Type: text/plain; charset=us-ascii X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.200.71.1.16\)) Subject: Re: [PATCH net 1/2] tcp: avoid wrapping Fast Open blackhole timeout From: Esko Mobius In-Reply-To: Date: Sat, 14 Nov 2026 20:41:59 +0800 Cc: Yingjie Wang , "netdev@vger.kernel.org" , "mptcp@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "edumazet@kernel.org" , "ncardwell@google.com" , "davem@davemloft.net" , "kuba@kernel.org" , "pabeni@redhat.com" , "horms@kernel.org" , "matttbe@kernel.org" , "martineau@kernel.org" , "geliang@kernel.org" , "ycheng@google.com" , "weiwan@google.com" , "stable@vger.kernel.org" Content-Transfer-Encoding: 7bit Message-Id: References: <340d9f1f96e235642e8b47b5e7c836a18de8dd56.1794325665.git.x-professor@outlook.com> To: Kuniyuki Iwashima X-Mailer: Apple Mail (2.3901.200.71.1.16) On Thu, 12 Nov 2026 06:15:12 +0000, Kuniyuki Iwashima wrote: > No one wants to configure 80 days blackhole timeout. > > Please apply a sane limit in proc_tfo_blackhole_detect_timeout(). When picking the limit, note that the product wraps long before 80 days. With HZ=1000 and the maximum multiplier of 64, 64 * timeout * HZ exceeds UINT_MAX once the timeout reaches 67109 seconds, about 18.6 hours. A limit of one day would still wrap. On 32-bit, time_before() also needs the interval to stay below 2^31 jiffies, so the current expression is only safe up to INT_MAX / HZ / 64 seconds, which is 33554 seconds (about 9.3 hours) with HZ=1000. So either the limit is derived from that, or the u64 computation with a clamp has to stay. The same applies to net.mptcp.blackhole_timeout in patch 2, which uses the same expression. Thanks, Yongjian