From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 C39F6206962; Tue, 8 Oct 2024 17:39:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728409149; cv=none; b=PwMuvt5dVXSSknXmNbYGesg3D+cFc0eeATUFKJR5w25Oxmsp2en157kwUC6lRyUWD2+t+ge7Gh2Bf1OIUtt1mF8V+nadYeq56UeBB7xRe3xHlFcBn3b7T2ii0VQkJln3/NaMLCsKKO9xJs3zgHo8CkmakvrSTspijZLZpWtc31s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728409149; c=relaxed/simple; bh=LeNmQrCvMNToDiO8+U1mr3Y/hn1bq2qDwFPHijzQuOA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hRpv7H0garhs1exO+4+tOGRXHlEqokOY2AV2TLnVXzhIuIG00jVL0NZYAE2l8babRI2TRJxw4Ly4+wROLRzVH3eMCc652kcuasdi99KT25amkhqQReuSmA25A3xtTPuoH/1gvvPj1SvjTF01Jx4XjCSOzpB5veU5yCzi6icBAF8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=DHDV2LrI; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="DHDV2LrI" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=LeNmQrCvMNToDiO8+U1mr3Y/hn1bq2qDwFPHijzQuOA=; b=DHDV2LrIIQAjuxu4quq9XxH46o +a5Kg93/BhPUz3F9q7f8t50MkOgIP1DTLW3DU6OFzSyGK8Q0dVmpvfhOKPErC45Q9Eo58KKDuOxHh di55iWcvYcx0HACbiD/NL/amMGbyIgMO3yST6fmC4eCVv/URiVSR5+/6ODRq2BBFNv6j1r4NLAT0l 3ommyHCh4yW4qVxGnmgDfIEacshrGs6n4HyYtxIQn3Js1ifFrCy1cSPDGA2H6di1GO0udaxbr+h/d H205lD65Imt6q8G0/p6mlGikpjWoWqKGcCXucMavT7cqGgKLaD5BDzUROzq4Jg603CML2WdiqW4U/ edq7GUiw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1syEAm-00000002qRG-0gZ3; Tue, 08 Oct 2024 17:39:01 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 93E47300599; Tue, 8 Oct 2024 19:38:59 +0200 (CEST) Date: Tue, 8 Oct 2024 19:38:59 +0200 From: Peter Zijlstra To: Juri Lelli 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: <20241008173859.GE17263@noisy.programming.kicks-ass.net> References: 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: 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.