From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B5789C4332F for ; Wed, 23 Nov 2022 22:38:02 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4NHbcS5n7bz3f3S for ; Thu, 24 Nov 2022 09:38:00 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=ZY/gsWR1; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=2604:1380:4641:c500::1; helo=dfw.source.kernel.org; envelope-from=frederic@kernel.org; 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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZY/gsWR1+ftH5DmBc5HB7/AUYXKs0bWvfWJvgxns0MX4s3BWaWwpRfSIcHTKcEYmV B0wnZtvhgasQ8QQHSG2F/yEhwaCYy/3vmu/4vnG8nq4qv5T9iXYwi7F1fpEvszTTcf ggzhMUVag7f+38J1um0MBp9jS9hA1pPCgTK/Py9Hhy8u29ScfdMKm2uZyK+oUqtJd+ 8rEbhdATPFXXMo7SgV5s6h3zBAoxoas3rl1taC6vt/YMWQMNG65L1l8Nz4+Xdr8qjM ZZs5fdUge3U1dKHzUFe13npiakAyb0XB4nMjOnuJv8TFbIbPmDC24lB5vTHpfUXuW3 gWhmggu4Bmpxg== Date: Wed, 23 Nov 2022 23:36:58 +0100 From: Frederic Weisbecker To: Zhouyi Zhou Subject: Re: [PATCH linux-next][RFC]torture: avoid offline tick_do_timer_cpu Message-ID: <20221123223658.GC1395324@lothringen> References: <20221121035140.118651-1-zhouzhouyi@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221121035140.118651-1-zhouzhouyi@gmail.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: dave@stgolabs.net, paulmck@kernel.org, fweisbec@gmail.com, josh@joshtriplett.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Nov 21, 2022 at 11:51:40AM +0800, Zhouyi Zhou wrote: > During CPU-hotplug torture (CONFIG_NO_HZ_FULL=y), if we try to > offline tick_do_timer_cpu, the operation will fail because in > function tick_nohz_cpu_down: > ``` > if (tick_nohz_full_running && tick_do_timer_cpu == cpu) > return -EBUSY; > ``` > Above bug was first discovered in torture tests performed in PPC VM > of Open Source Lab of Oregon State University, and reproducable in RISC-V > and X86-64 (with additional kernel commandline cpu0_hotplug). > > In this patch, we avoid offline tick_do_timer_cpu by distribute > the offlining cpu among remaining cpus. > > Signed-off-by: Zhouyi Zhou > --- > include/linux/tick.h | 1 + > kernel/time/tick-common.c | 1 + > kernel/time/tick-internal.h | 1 - > kernel/torture.c | 10 ++++++++++ > 4 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/include/linux/tick.h b/include/linux/tick.h > index bfd571f18cfd..23cc0b205853 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -14,6 +14,7 @@ > #include > > #ifdef CONFIG_GENERIC_CLOCKEVENTS > +extern int tick_do_timer_cpu __read_mostly; > extern void __init tick_init(void); > /* Should be core only, but ARM BL switcher requires it */ > extern void tick_suspend_local(void); > diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c > index 46789356f856..87b9b9afa320 100644 > --- a/kernel/time/tick-common.c > +++ b/kernel/time/tick-common.c > @@ -48,6 +48,7 @@ ktime_t tick_next_period; > * procedure also covers cpu hotplug. > */ > int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT; > +EXPORT_SYMBOL_GPL(tick_do_timer_cpu); Please rather make a function for this. This is an internal value that we don't want to expose to modules. This can be: int tick_nohz_full_timekeeper(void) { if (tick_nohz_full_enabled() && tick_do_timer_cpu >= 0) return tick_do_timer_cpu; else return nr_cpu_ids; } And then just check if the value is below nr_cpu_ids. Thanks.