From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B7BC33812EB; Fri, 26 Jun 2026 16:05:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782489926; cv=none; b=QP3KwFz8QzFrp3Qn5pEIjH9eCIPFKpd9RbhUsyvkeY8jKIbI2N2iUoF1jwZChOHEV20/ReElQDB1RJLkZ4Hef+MP26rWDpGIyEu0j/D+MAZyyphLudHVBXUQerz8CgcaSjiLhm5h4Q8Vix8rDPtkdiIdGRhlEYAzOp3NFJF6DU8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782489926; c=relaxed/simple; bh=fzet0BfZ5liznQQD86D86jm9+I5k6NDc+MubaimMd6M=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XrHH3JSOUQT84qWf9Ko7awuYrV9vkbMj9miKfgl4HPSosFKJ05TIsVxI8IZX/7KokmeJxDQvBVuxbGaXW6FgK8tG75YFLzorVbxPMYAbXTdnRjKC9kCezvP/3NrqPB4i2d9lPqD8lBqBL4b8y1QhV1MdyOwCwJ5d8uJKcFzmJ9o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ikBDEUN0; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ikBDEUN0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 528011F000E9; Fri, 26 Jun 2026 16:05:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782489925; bh=MQxhqWJDp3E2oy2FCt/1Pb6g2ywBUfWHcqVmGNlFYWQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=ikBDEUN0N96urrn/HhcKcG93mc4rufDhJ/DYa3WB1aOI3fEVoRmlpV4o7RTb73Swv pOCbe4OEinzl1bj/n/2NTQfB3k8RqIhUmWJ017+6ylpT7ErotNpis1YZjLJqouXay8 RipQnwIzPwwTO1mGzpvIK0WuO62J2RfLQ/sUjAVrTJXBmWbbnd0WpOZDvaVUJZjKGG 0X9xxZocsPEZzd04VvhAcmrX4BVsaVVblP3CsPRVAsVtTzJmz/udL8yQTUE14/xt+Y wT4vNMpHgfT+fUBC2Ydtm61bZ4UXzL5NWiG4apcF2e0kZ1w3O7nKr/Fb/J2wOKZGCX Ytt2aG14PPCCA== Date: Fri, 26 Jun 2026 10:05:23 -0600 From: Keith Busch To: Jens Axboe Cc: Ben Carey , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [BUG] RCU hang with io_uring nvme polling Message-ID: References: <20260626150946.287781-1-benjamin.james.carey3@gmail.com> <85d1f999-7778-4c74-9d72-b8ac8500de31@kernel.dk> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <85d1f999-7778-4c74-9d72-b8ac8500de31@kernel.dk> On Fri, Jun 26, 2026 at 09:17:35AM -0600, Jens Axboe wrote: > On 6/26/26 9:09 AM, Ben Carey wrote: > > From a running QEMU image with the latest kernel: > > 1. Attach GDB to the running instance. > > 2. Enable io polling via sysfs (echo 1 > /sys/block/nvme0n1/queue/io_poll). > > That's not how that works at all. You need to setup poll queues on the > nvme driver side, using the nvme.poll_queues=XX kernel parameter, or if > using nvme as a module, load the module with poll_queues=XX where XX is > the number of poll queues. You're not doing any polled IO as-is, and the > above should also have dumped a dmesg message about how that does > absolutely nothing. > > That said, it should still work, just not doing polled IO. I'll take a > look sometime next week, OOO right now. Yeah, the sysfs attribute does nothing, but Ben mentioned they had the correct kernel command line: BOOT_IMAGE=/vmlinuz-7.1.0-g3996771b8f75 root=/dev/mapper/ubuntu--vg-ubuntu--lv \ ro nvme.poll_queues=1 nokaslr So they did enable polling, but the "echo" step is just confusing and unnecessary. I tried out the test, and there does appear to be a problem here, so I'm looking into it.