From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 012BA42070; Wed, 9 Oct 2024 07:22:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728458546; cv=none; b=u/BQIZr+NHlPnlg6a0vZbBOGiMEc1WNDv6NkpScMYavO2/alJfRWp66BWSFqiVcgcM4wBHMo7y72NT7KxchNan3XLwCIwm0yoxGVaJZghyBhW2tvxmxsEmHgkKbSq64+TsFTuLySEPHnGmFDWoVcrFaJiV0li/jWk7/WFbAecyw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728458546; c=relaxed/simple; bh=lU1+TGOSZjngrtvNvSYAx/4I9ejYNHXcu2cBGk+S0S8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eq6EOdK04yJUgQW4zY06m7vToSD+C/kZkkl6l15lNx83F8Yoyt1UOgLpvX7pQfCO0XRBjbaKnmnFrTeg9ujDphcOfT0e16JDXx9lDBJr2cwpGekLU+J1FbAbdRXvLqmqXrD7lZw3YOXUCSk8jRIqe7QMxZKGezpBPjqr/8Y9gWw= 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=oFbNVdZY; arc=none smtp.client-ip=90.155.92.199 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="oFbNVdZY" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=hKTdrQqY1KerlqZ8NVlYllQr1UgAK/tqStYcq4dnlvs=; b=oFbNVdZYqt8+/2Y3DSehiJOWwE SLJKapBIMcFjUI/j9fHGPLmJeVp2UUyxqmyKz3LtNlZEZ3Yn3+3zq9nxa7wC/t4xtRsg4m+JHDcyx OAnthj+rVFjB5rxqaVpwkBMLpYCpTWSoMguVTVh5dEzHzsLKvzG2AoQiFF6TEBNMDavoj6xG4qkU7 8+Pp6EmyInA4V6PHV+AQOsbNqwrtvFCTl+tq+w3fcGbtHzT8e/blP162ANfMdKB7wf45vQyzV6M3X SnEo52kSR/w1H0f2ZklwXyY/zfp9IUZv8V2Q0eZTsLYMDHQVEn11hJZAxPo5PwOI+6dfnXMs2K6Av hL6EU/0w==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1syR1S-00000004q77-2P5s; Wed, 09 Oct 2024 07:22:14 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id F15B73004AF; Wed, 9 Oct 2024 09:22:13 +0200 (CEST) Date: Wed, 9 Oct 2024 09:22:13 +0200 From: Peter Zijlstra To: Waiman Long Cc: Thomas Gleixner , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?iso-8859-1?Q?Andr=E9?= Almeida , LKML , linux-rt-users , Valentin Schneider , Sebastian Andrzej Siewior , Juri Lelli Subject: Re: Futex hash_bucket lock can break isolation and cause priority inversion on RT Message-ID: <20241009072213.GF17263@noisy.programming.kicks-ass.net> References: <20241008173859.GE17263@noisy.programming.kicks-ass.net> <5f125ed8-66bb-4654-b1da-b8db643b81d6@redhat.com> 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: <5f125ed8-66bb-4654-b1da-b8db643b81d6@redhat.com> On Tue, Oct 08, 2024 at 03:44:23PM -0400, Waiman Long wrote: > > 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. They're on the todo list somewhere... I know Ampere had interest, other than that nobody really said anything.