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 BC3E933CEB4; Wed, 18 Feb 2026 09:41:00 +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=1771407665; cv=none; b=hEFnWCkIcmcIO8fgNI+swnxqa9amgG9VZEAl0rXk3yHZiJbBAHlp9e78oWd+py6J3p2aWC2/KS/tm+5IkOdL0N1QSigd3cY30Bpg5jpI9HMJPA4tiOV5anWUagN4pESuRFnAwyK1FNI51ut2z5oJ6U8htSQgpoeTDQRjHIoTolc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771407665; c=relaxed/simple; bh=NDFJbk/BFwqHVibRykzi/FgFqV0F/XEySGpaSVYH6KI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HCrPvGpl3uy/c5+XtN0KoNAcSopoZnHDVCeup2bP1AZb9qqiuqUW4wRw1pGG1uxhZoIYEHQ6ml+WF41NCUrqpG+tfqMvNktVtn+bYbKh6oZWAv1zQdJpvW9UKPY01UYZc9QWyMd+79VXgQKX7XP7m/PlIlfcU11nri2BjHGmwI4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (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=Y+gnN5g9; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (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="Y+gnN5g9" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=lBwtclkQaCgMpl8CdrtjyAqZW8zWsY/Zj7WJgl0YaFk=; b=Y+gnN5g9BP1HlrJDN9aNVNepS3 XHvXHu0UW+yDKqpCv2ZnWtUUsyvw+WOqiGp9KMO4/AAUCr+s+i3JtjfxvqB5CVeXifIUPNyKaR2tx ZEHXki0tRJCT+Zh+MrdaHUX2xZxRrUocec1JfSRY2wUEA/HwFcB8cByBu1gl+gWdi2fF5U6uOkmnF NM1EqeTXeLJkAL5bJcCVsA7TcBWlOqQsr//PdPHZD2Ay8mY8h91ONSpdwlBQhcbDpUen3pT8yCNrj Yk8g/F/OpA0MfirgQhSJL0nqUn3/wXOCXo0oEBjxvOK6Mr75agzoGJvz/mArgrDCjG5XnCLBGrNU6 WtipYRrw==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vse3D-00000005pMO-0i9o; Wed, 18 Feb 2026 09:40:55 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CCF2F3004AB; Wed, 18 Feb 2026 10:40:53 +0100 (CET) Date: Wed, 18 Feb 2026 10:40:53 +0100 From: Peter Zijlstra To: Sean Christopherson Cc: kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Ingo Molnar , sched-ext@lists.linux.dev, aubrey.li@linux.intel.com, yu.c.chen@intel.com Subject: Re: [linus:master] [sched/core] 704069649b: kernel-selftests.kvm.hardware_disable_test.fail Message-ID: <20260218094053.GD2995752@noisy.programming.kicks-ass.net> References: <202602122157.4e861298-lkp@intel.com> <20260213144417.GL3016024@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Feb 13, 2026 at 02:14:14PM -0800, Sean Christopherson wrote: > On Fri, Feb 13, 2026, Peter Zijlstra wrote: > > On Thu, Feb 12, 2026 at 10:08:04PM +0800, kernel test robot wrote: > > > Hello, > > > > > > we found the kernel-selftests.kvm.hardware_disable_test failed consistently upon > > > this commit but pass on parent. unfortunately, we didn't find many useful > > > information in dmesg. this report is just FYI what we observed in our tests. > > > > > > kernel test robot noticed "kernel-selftests.kvm.hardware_disable_test.fail" on: > > > > With the caveat of PEBKAC (it is Friday after all); I can't reproduce. PEBCAK indeed, I managed to consistently boot into the bad kernel :-( So never actually tested the good one. > > That is, ./hardware_disable_test as build from cee73b1e840c, doesn't > > work for me on 704069649b5b^1 either. > > > > Sean; is there a magic trick to operating that test, or is it a known > > trouble spot? > > Hmm, shouldn't require any magic, and hasn't been known to be flaky. > > This very decisively points at 704069649b5b ("sched/core: Rework > sched_class::wakeup_preempt() and rq_modified_*()"). on my end as well. With > that commit reverted, the below runs in ~40ms total. With 704069649b5b present, > the test constantly stalls for multiple seconds at sem_timedwait(). > > AFAICT, the key is to have the busy_loop() pthread affined to the same CPU as > its parent. The KVM pieces of the selftest have nothing to do with the failure. > > Here's a minimal reproducer that you can build without selftests goo :-) > E.g. `gcc -pthread -o busy busy.c` should work. Whee, thanks! OK, let me go prod at this with something sharp, see what falls out.