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Fri, 26 Jun 2026 09:35:57 -0700 (PDT) Message-ID: <94614dd9-9351-4a64-83dc-4fc87e377e59@kernel.dk> Date: Fri, 26 Jun 2026 10:35:56 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] RCU hang with io_uring nvme polling To: Keith Busch Cc: Ben Carey , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260626150946.287781-1-benjamin.james.carey3@gmail.com> <85d1f999-7778-4c74-9d72-b8ac8500de31@kernel.dk> <1932a509-4e27-485e-8e09-1da67e0082c8@kernel.dk> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/26/26 10:33 AM, Keith Busch wrote: > On Fri, Jun 26, 2026 at 10:06:49AM -0600, Jens Axboe wrote: >> Ah good catch, I missed that. Should've grepped! In general, IO should >> either get polled, or if the device is misbehaving, then timeouts will >> catch it. That said, haven't looked at the actual report yet, will do >> so next week (unless you beat me to it...?) > > I'll give it a shot! > > The test has 1 polling queue with 2 jobs dispatching. One of the job's > polled the completions for both. The other job is polling for no reason > at all with nothing outstanding. The only thing that can break us out of > that loop now is need_resched(), but that appears to never return true. Yes, it's a bad configuration. I bet it's as simple as: https://lore.kernel.org/linux-block/20260617155051.1266079-1-anuj20.g@samsung.com/ but in practice nobody should configure a single poll queue and run multiple jobs, particularly not when the object is framed around "energy efficiency" as this configuration is pretty much guaranteed to waste 2 cores, with most of the time going towards spinning on a lock rather than doing potentially useful work. -- Jens Axboe