From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 C39AF165FCD for ; Thu, 18 Apr 2024 14:50:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713451816; cv=none; b=bUZDohopiBC/es4/wMclMWP1autC0jjj8YBbk6roKgdyniIPzixZ2Zk8fAjtbd38DB3id8UP+tAQ8RrxVyZSufoDFwjmiBjZumezErtaZy55lBsSegKBhtbbMtvBWpl8gwodN/hqhPXuEaTUx9kzq3X9c//eNqm6TEyjgpumpyc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713451816; c=relaxed/simple; bh=OmM4Ol2cehc696v2G5IaKMs3D22emCXT7jfMzKndz4s=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=AOy0kZ3EAWOGsu7wOxqNo7Hjosl1QyA/ad0HhFqzW1HrLuO/yhIWOBw2ePTowrq+fg/hlM6hDM75psibH35HCz6lhloAHWwNfkTz4oszcV7z7joOQpdP1wYxKawLeECjxPAEu80WoNpi7Uw3biP9eQTjCBe7JYZs6iec2DqRddE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=BauijufJ; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BauijufJ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1713451813; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=iA26oegDx20/Oc13YNzcYkvxMaaemAyNcLhc+rMuX3A=; b=BauijufJhpNV0FEVOL1QASyPrFyzC3fd1+toDN7UFNqnRAsx75mSidPeW78/UXk4cfp1Lq iQTMGvaaLa3heMVDUoRmcQAGFfUmGD4fJXgH4u240k8qakQ/W8lt4UFL3mopivfLfjaaJ0 XLmbDSxO+vBZ8So1lpmEQbac8uq30TQ= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-461-FBi5yr9LP8mOk6bxUDwbfw-1; Thu, 18 Apr 2024 10:50:10 -0400 X-MC-Unique: FBi5yr9LP8mOk6bxUDwbfw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 454A6286A9C2; Thu, 18 Apr 2024 14:50:09 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.39.195.76]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CF95B40C1233; Thu, 18 Apr 2024 14:50:05 +0000 (UTC) Date: Thu, 18 Apr 2024 10:50:02 -0400 From: Phil Auld To: Oleg Nesterov Cc: Frederic Weisbecker , Nicholas Piggin , Leonardo Bras , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Tejun Heo , Lai Jiangshan , linux-kernel@vger.kernel.org, Junyao Zhao , Chris von Recklinghausen Subject: Re: [PATCH] sched/isolation: fix boot crash when the boot CPU is nohz_full Message-ID: <20240418145002.GC29188@lorien.usersys.redhat.com> References: <20240130010046.2730139-2-leobras@redhat.com> <20240402105847.GA24832@redhat.com> <20240411143905.GA19288@redhat.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: <20240411143905.GA19288@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 On Thu, Apr 11, 2024 at 04:39:05PM +0200 Oleg Nesterov wrote: > Documentation/timers/no_hz.rst states that the "nohz_full=" mask must not > include the boot CPU, this is no longer true after the commit 08ae95f4fd3b > ("nohz_full: Allow the boot CPU to be nohz_full"). > > However after another commit aae17ebb53cd ("workqueue: Avoid using isolated > cpus' timers on queue_delayed_work") the kernel will crash at boot time in > this case; housekeeping_any_cpu() returns an invalid cpu nr until smp_init() > paths bring the 1st housekeeping CPU up. > > Change housekeeping_any_cpu() to check the result of cpumask_any_and() and > return smp_processor_id() in this case. Yes, this is just the simple and > backportable workaround which fixes the symptom, but smp_processor_id() at > boot time should be safe at least for type == HK_TYPE_TIMER, this more or > less matches the tick_do_timer_boot_cpu logic. > > We should not worry about cpu_down(); tick_nohz_cpu_down() will not allow > to offline tick_do_timer_cpu (the 1st online housekeeping CPU). > > Fixes: aae17ebb53cd ("workqueue: Avoid using isolated cpus' timers on queue_delayed_work") > Reported-by: Chris von Recklinghausen > Closes: https://lore.kernel.org/all/20240402105847.GA24832@redhat.com/ > Signed-off-by: Oleg Nesterov Checking the returned value instead of assuming seems safer in any case. Reviewed-by: Phil Auld > --- > Documentation/timers/no_hz.rst | 7 ++----- > kernel/sched/isolation.c | 11 ++++++++++- > 2 files changed, 12 insertions(+), 6 deletions(-) > > diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst > index f8786be15183..7fe8ef9718d8 100644 > --- a/Documentation/timers/no_hz.rst > +++ b/Documentation/timers/no_hz.rst > @@ -129,11 +129,8 @@ adaptive-tick CPUs: At least one non-adaptive-tick CPU must remain > online to handle timekeeping tasks in order to ensure that system > calls like gettimeofday() returns accurate values on adaptive-tick CPUs. > (This is not an issue for CONFIG_NO_HZ_IDLE=y because there are no running > -user processes to observe slight drifts in clock rate.) Therefore, the > -boot CPU is prohibited from entering adaptive-ticks mode. Specifying a > -"nohz_full=" mask that includes the boot CPU will result in a boot-time > -error message, and the boot CPU will be removed from the mask. Note that > -this means that your system must have at least two CPUs in order for > +user processes to observe slight drifts in clock rate.) Note that this > +means that your system must have at least two CPUs in order for > CONFIG_NO_HZ_FULL=y to do anything for you. > > Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded. > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > index 373d42c707bc..2a262d3ecb3d 100644 > --- a/kernel/sched/isolation.c > +++ b/kernel/sched/isolation.c > @@ -46,7 +46,16 @@ int housekeeping_any_cpu(enum hk_type type) > if (cpu < nr_cpu_ids) > return cpu; > > - return cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask); > + cpu = cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask); > + if (likely(cpu < nr_cpu_ids)) > + return cpu; > + /* > + * Unless we have another problem this can only happen > + * at boot time before start_secondary() brings the 1st > + * housekeeping CPU up. > + */ > + WARN_ON_ONCE(system_state == SYSTEM_RUNNING || > + type != HK_TYPE_TIMER); > } > } > return smp_processor_id(); > -- > 2.25.1.362.g51ebf55 > > > --