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 756F2429CCE; Wed, 12 Aug 2026 10:35:56 +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=1786530958; cv=none; b=b6mQnlLdG6L0My/Nhg28hiLyIuhVkgSQfiz/Ji9NpzjXS6QQXcuSkEfhxaU4WKTKdu9dJnbdSAbXcykPvipLbNK8D4i18A1rtbmo7WI2HJIK1GWG14ezneGftgvc6Gse29kS0S0c1JV6Ug1ZIPvgJn6iC4OwqYn7RNPIW+IctxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786530958; c=relaxed/simple; bh=vPm3grlkHc6pD440XBA+E8sxb6nAqTB/ADO9KDCPaPw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Q1ko4WWmiWEFIkh7VL4qzfKlhiEaSO4UCx+500X8bLK1DXeUr754X4IqfuXVkVbJBo4922iQ3r2tSfnJT6txzasHGmB5gXFttwGf9CLJGvM+gJz1q2EfvnS4Ohp+yibGJJrDecAFf778qXEtn+kEOlAeNfrqUEE3nHQg/W9kZyk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=I5fZP8EJ; 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=pass 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="I5fZP8EJ" 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=3COCkry9q8e+KkRgduBrjMvDdbbEHNdYJdq2BIpVdRQ=; b=I5fZP8EJwRd5SV0eyb9nBMypxr hf+Z6d8SUxaH57ANiJhNoRv1ru/BV2iXPPXVpGfG7Tbgf9YwWfa5abZ4sNG6OvjCmSOMBwzK2Cf+F 6nQhS+oQqz9AR6kPrnZAMSy9eOSfVsOLnQDi63yQscQ6FlXWX3crzllTEOjMM/cqE1d57uHBH0NLx YVzOqRY2zKWActZlfGCLekftSGhS0kDrOV86cEHLBbQARh1gke255FGmZkocFcuuXHzPDPUFCYUl5 yA2r9pP+VAYEj4tKZUu4Ix40H0MzasRCH9F+73rrt3gzEpEcv89guqSR6v6kFYFzivfKRC4Tvuy1h hDfseKJg==; 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 4.99.1 #2 (Red Hat Linux)) id 1wu6JD-00000001pQA-32vM; Wed, 12 Aug 2026 10:35:44 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 5E73D3012AB; Wed, 12 Aug 2026 12:35:43 +0200 (CEST) Date: Wed, 12 Aug 2026 12:35:43 +0200 From: Peter Zijlstra To: Karl Mehltretter Cc: Andrew Morton , Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , Marco Elver , Bradley Morgan , Anna-Maria Behnsen , Frederic Weisbecker , Thomas Gleixner , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Sebastian Andrzej Siewior , Clark Williams , linux-rt-devel@lists.linux.dev, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 5/6] sched/core: Pause KCOV in try_to_wake_up() Message-ID: <20260812103543.GH776954@noisy.programming.kicks-ass.net> References: <20260811154111.64669-1-kmehltretter@gmail.com> <20260811154111.64669-6-kmehltretter@gmail.com> 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: <20260811154111.64669-6-kmehltretter@gmail.com> On Tue, Aug 11, 2026 at 05:41:10PM +0200, Karl Mehltretter wrote: > try_to_wake_up() is uninstrumented, but it calls instrumented helpers > such as kthread_is_per_cpu(), CPU capacity helpers and SCHED_HRTICK > arming. They can record into current while in_task() is true. > > CONFIG_KCOV_SELFTEST exposes this under PREEMPT_RT. The interrupt > selftest fails on x86_64 in kthread_is_per_cpu(): RT runs the timer > softirq in a thread, so the wakeup runs in task context during the > selftest's spin. The same helpers leak into non-RT syscall wakeups such > as a pipe write waking a reader. > > Pause the wakeup body with the kcov_pause guard. Wrapping only > select_task_rq() would miss SCHED_HRTICK arming during enqueue. > > Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") > Assisted-by: Claude:claude-fable-5 > Signed-off-by: Karl Mehltretter > --- > Notes: > v2: > - take guard(kcov_pause)() > - describe the paused wakeup body precisely > > kernel/sched/core.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index e49f0bfa0ca73..e863fac02e38f 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4253,6 +4253,9 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > guard(preempt)(); > int cpu, success = 0; > > + /* Instrumented callees would leak coverage into current. */ > + guard(kcov_pause)(); Same problem again. All of this code is instrumented.