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[80.47.4.206]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6cba4752828sm43626336d6.95.2024.10.09.01.26.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Oct 2024 01:26:50 -0700 (PDT) Date: Wed, 9 Oct 2024 09:26:45 +0100 From: Juri Lelli To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?iso-8859-1?Q?Andr=E9?= Almeida , LKML , linux-rt-users , Valentin Schneider , Waiman Long , Sebastian Andrzej Siewior Subject: Re: Futex hash_bucket lock can break isolation and cause priority inversion on RT Message-ID: References: <20241008173859.GE17263@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241008173859.GE17263@noisy.programming.kicks-ass.net> Hi Peter, On 08/10/24 19:38, 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. Ah yes indeed. Just thought that if we have ideas on how to possibly make this better it might still be worthwhile, even if it won't fix all issues. > I do have some futex-numa patches still pending, but they won't > magically sure this either. Userspace needs help at the very least. Thanks! Juri