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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5390EB64D0 for ; Tue, 13 Jun 2023 14:01:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242450AbjFMOBS (ORCPT ); Tue, 13 Jun 2023 10:01:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56446 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239765AbjFMOBP (ORCPT ); Tue, 13 Jun 2023 10:01:15 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C882EF4 for ; Tue, 13 Jun 2023 07:01:14 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5DEBD63523 for ; Tue, 13 Jun 2023 14:01:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0EBAFC433F0; Tue, 13 Jun 2023 14:01:12 +0000 (UTC) Date: Tue, 13 Jun 2023 10:01:11 -0400 From: Steven Rostedt To: LKML , x86@kernel.org Cc: Masami Hiramatsu , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Borislav Petkov Subject: Re: [PATCH v2] x86/alternatives: Add cond_resched() to text_poke_bp_batch() Message-ID: <20230613100111.44a7c43a@gandalf.local.home> In-Reply-To: <20230531092419.4d051374@rorschach.local.home> References: <20230531092419.4d051374@rorschach.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter, Can you ack this? And then I can push it through my tree. Thanks! -- Steve On Wed, 31 May 2023 09:24:19 -0400 Steven Rostedt (by way of Steven Rostedt ) wrote: > From: "Steven Rostedt (Google)" > > Debugging in the kernel has started slowing down the kernel by a > noticeable amount. The ftrace start up tests are triggering the softlockup > watchdog on some boxes. This is caused by the start up tests that enable > function and function graph tracing several times. Sprinkling > cond_resched() just in the start up test code was not enough to stop the > softlockup from triggering. It would sometimes trigger in the > text_poke_bp_batch() code. > > When function tracing enables all functions, it will call > text_poke_queue() to queue the places that need to be patched. Every > 256 entries will do a "flush" that calls text_poke_bp_batch() to do the > update of the 256 locations. As this is in a scheduleable context, > calling cond_resched() at the start of text_poke_bp_batch() will ensure > that other tasks could get a chance to run while the patching is > happening. This keeps the softlockup from triggering in the start up > tests. > > Signed-off-by: Steven Rostedt (Google) > --- > Changes since v1: https://lkml.kernel.org/r/20230528084652.5f3b48f0@rorschach.local.home > > - Just call cond_resched() once in text_poke_bp_batch() and not for > each phase, as it only needs to be called once every 256 entries. > > arch/x86/kernel/alternative.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index f615e0cb6d93..412ad66cd240 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -1953,6 +1953,16 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries > */ > atomic_set_release(&bp_desc.refs, 1); > > + /* > + * Function tracing can enable thousands of places that need to be > + * updated. This can take quite some time, and with full kernel debugging > + * enabled, this could cause the softlockup watchdog to trigger. > + * This function gets called every 256 entries added to be patched. > + * Call cond_resched() here to make sure that other tasks can get scheduled > + * while processing all the functions being patched. > + */ > + cond_resched(); > + > /* > * Corresponding read barrier in int3 notifier for making sure the > * nr_entries and handler are correctly ordered wrt. patching.