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[109.243.148.111]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c0c615089desm539333166b.54.2026.06.23.06.36.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Jun 2026 06:36:40 -0700 (PDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Authentication-Results: eu.smtp.expurgate.cloud; dkim=pass header.s=20251104 header.d=gmail.com header.i="@gmail.com" header.h="Content-Transfer-Encoding:In-Reply-To:From:Content-Language:References:Cc:To:Subject:User-Agent:MIME-Version:Date:Message-ID" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1782221801; x=1782826601; darn=lists.xenproject.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=b3/AJFEfESGynlXm7mwdZdVu6m4rYWwrCxe79kOK9Ww=; b=f8RnwcnU8JaNLeBnPF29imL3+jTgGvg8+buJ49YBfhFQ+Z2zRZQ0lV4c8kjyK1J1Fy 21Hq4V9IGfr1Ikt1B/Qp3dWodL2iHoG1X9uavC5C+gMHnU/8CCLDvxCr5EcZn5JXjLtT dq/SRBV3LdVMG6AWs8Xamvmohx2gleptWiRCpYn3vNpag7+q25HztrTGrCpgQydPEBUq s++PQaO/eTj7zrYH239Dahn/5QuYJCFvfVvc2c+eYCsxNsNLVfaSEf4u1twYCoT3Rilq 4amJUonrrb68jtrJGWvKroSC04lhvrPYHa0oe8ycGT7/sLf9mdbe3w2ZsV5CYJk3VBfZ PLmg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782221801; x=1782826601; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=b3/AJFEfESGynlXm7mwdZdVu6m4rYWwrCxe79kOK9Ww=; b=KmB1wVzS1uQad7HdAZ2AWQRyrSiHeBPNk57tZtBUW+HGtOnzEcV4ldEYpsUCpirbXw iPjkymD7z+Tnqdguf63pbp/Gv9/JoHeouW3MVsCp9JPXlcipmT3pJW6iklqs7MWfIbGo ZDMmBbV65vhHfIBgA7rYGHE5n1AEObAdxbIB5Y4Bl+aDoDqUdU+vqIIO7tmDv9YteTAg rvuSZ7UxP0NsR4saUC2J6cQEy+mnvxZ5Qk40JEjLXIoZnphsVDcG0IForzb4eSJ/eC5a WrCky/SJ0vwxCjIlbuUNkiT40ycBy0yDhZdtRx0UUAD8w9b3hBiCA351MAVot87GXNNm OYbQ== X-Forwarded-Encrypted: i=1; AFNElJ/3MQpB+kzJYCZ0z1PPkiJq0mOm9i13SbpbdEs35pg+PsI+ELQp+I9WOxynUWZZDIZHZl1YPfdXUA8=@lists.xenproject.org X-Gm-Message-State: AOJu0YwHTezj5IzaTFlbbc+FAlBOOueI08AaXr24y1M6UpsbA0MdVk2E 2q5+jMZSiU3yg82uZX2K6pn+2NzIIhEcLiiIVdfOJ5jmfxthpqYg9SVZ X-Gm-Gg: AfdE7ckRykS3KtJmAZwxC1X3XQfqaZK0xC6NT1PydBH4+TK7baPPm3ZweJLCFobVETh VUmXEdTs6SYd/gIa/lB5sbyVITyMOpXNf0snei14sLvmSNcIFzOGR7UngRA38lxkB1wG229l8ff 8RXzYaTAiQXU2PsP5S1dhnn6H3vCgipCpXgPLIAbFuIDO8Gpw3dLa0bvCYP+DPofopeGelNHLjE n2EhzYFfxQdCn+hPPczQWBUo4BqLAaB2tNlRMLmLlmXAxIwoGFjor7IqUYEX1GYP2qp4Zk4cO2t 1nQ9kMhXgzf0LRalx52ZCvnS/PHMJJiYzM0yrHvfVXoglBYtyztdOV4CUn35XUlmIljYQjjzbHi C7RitlqrMgTIJIowRqtcKheFBw1PRLbl+gHaGJREQRnfn56UElaro7SGX+F2SfPPP+GXxrbicK9 2ePXuT8J4JWqQUPeJObDY0tizqsZORyesRlQzYMwwxyty8BZgBRXPGpVVIK/jcv2UfoXShNGtCp cpenw== X-Received: by 2002:a17:907:c07:b0:c0e:883e:e4f2 with SMTP id a640c23a62f3a-c0e883eea07mr481839866b.30.1782221800838; Tue, 23 Jun 2026 06:36:40 -0700 (PDT) Message-ID: <20161bd5-a081-4562-a1d9-14dbdba109f3@gmail.com> Date: Tue, 23 Jun 2026 15:36:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH for-4.22] char/ns16550: bound execution time of ns16550_interrupt() To: Roger Pau Monne , xen-devel@lists.xenproject.org Cc: Andrew Cooper , Anthony PERARD , Michal Orzel , Jan Beulich , Julien Grall , Stefano Stabellini References: <20260623103145.76383-1-roger.pau@citrix.com> Content-Language: en-US From: Oleksii Kurochko In-Reply-To: <20260623103145.76383-1-roger.pau@citrix.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-purgate-ID: tlsNG-d25034/1782221801-DB1EEABF-D9F25515/10/73395122804 X-purgate-type: spam X-purgate-size: 1453 On 6/23/26 12:31 PM, Roger Pau Monne wrote: > The current logic in ns16550_interrupt() will loop until the device sets > the NOINT in IIR. At least on the Lenovo ThinkSystem SR630 V4 the flow > control of the serial-over-lan emulated UART seems to be broken, as it > doesn't set the NOINT bit consistently. The Transmitter Holding Register > Empty in LSR also seems to not be properly signaled, as even with it set > writes to the transmit register take ~6ms. This leads to the watchdog > triggering very easily on such system. > > Introduce an upper bound on the execution time of ns16550_interrupt(), this > is currently set as 4x the polling interval, which is calculated as the > time to fill RX FIFO and/or empty TX FIFO. The current maximum is 5ms. > Once the timeout triggers the interrupt is disabled and the uart is > switched to polling mode. > Don't you mmiss Fixes: tag? > Signed-off-by: Roger Pau Monné > --- > There's a possible alternative approach to solve this by moving the actual > interrupt processing to a softirq tasklet and disabling the interrupt > source until the processing is done, likely unifying the logic with the > timer task. However that's a bigger change, and too risky for 4.22 at this > point. > --- Agree, it would be better to stick to the current solution: Release-Acked-by: Oleksii Kurochko Thanks. ~ Oleksii