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([2601:188:ca00:a00:f844:fad5:7984:7bd7]) by smtp.gmail.com with ESMTPSA id 8926c6da1cb9f-4db6eb358b0sm1769091173.29.2024.10.08.12.44.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Oct 2024 12:44:25 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <5f125ed8-66bb-4654-b1da-b8db643b81d6@redhat.com> Date: Tue, 8 Oct 2024 15:44:23 -0400 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: Futex hash_bucket lock can break isolation and cause priority inversion on RT To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?UTF-8?Q?Andr=C3=A9_Almeida?= , LKML , linux-rt-users , Valentin Schneider , Sebastian Andrzej Siewior , Juri Lelli References: <20241008173859.GE17263@noisy.programming.kicks-ass.net> Content-Language: en-US In-Reply-To: <20241008173859.GE17263@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/8/24 1:38 PM, Peter Zijlstra wrote: > On Tue, Oct 08, 2024 at 04:22:26PM +0100, Juri Lelli wrote: >> Does this report make any sense? If it does, has this issue ever been >> reported and possibly discussed? I guess it’s kind of a corner case, but >> I wonder if anybody has suggestions already on how to possibly try to >> tackle it from a kernel perspective. > Any shared lock can cause such havoc. Futex hash buckets is just one of > a number of very popular ones that's relatively easy to hit. > > I do have some futex-numa patches still pending, but they won't > magically sure this either. Userspace needs help at the very least. Regarding the futex-numa patches, are you planning to get them merged soon? We have customers asking for that. Cheers, Longman