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 8944FC4167D for ; Tue, 31 Oct 2023 10:19:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343602AbjJaKTI (ORCPT ); Tue, 31 Oct 2023 06:19:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229934AbjJaKTG (ORCPT ); Tue, 31 Oct 2023 06:19:06 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95BB983; Tue, 31 Oct 2023 03:19:04 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF366C433C8; Tue, 31 Oct 2023 10:19:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1698747544; bh=83ff9t5GCQi9LOG5AEcLmIHSOIfxWn+23hXnudO34gw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=aDi4pR+R28eO1zaLyqiV8wJNzoTJXHMmD+itcI8WaI9n10K8Jfd9up7scbAtkpjbz 3fVA8GjwnD2Ggc98CW6OyR4svLaKG+Q9xA3c89AENdNlhLfS8AP31G4xz3xmrBDZsw Vk4k3pFIgyTaGkWrEzytwPeZVv2Y2jS0DL/7uOzJfyxQZ98SwlA7YqTnWiKUwc4puW PTBSSjbT0AeRJ8dZw/wl/za2wURYC7oDUGszeekBcr8lLF/aYR4P2Md0sXkBAwQ6qR VYgPuiGPP0oZvHlDFST+ZcGXtd48zHCuuYzDzXHtuB8GdHXk8+J8GHQ3BJoX6lVAYf BHMsiNguKjVpQ== Date: Tue, 31 Oct 2023 11:19:01 +0100 From: Frederic Weisbecker To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "Paul E. McKenney" , rcu@vger.kernel.org, Boqun Feng , Joel Fernandes , Neeraj Upadhyay , Uladzislau Rezki , Z qiang Subject: Re: [GIT PULL] RCU changes for v6.7 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 30, 2023 at 06:12:51PM -1000, Linus Torvalds wrote: > On Fri, 27 Oct 2023 at 01:33, Frederic Weisbecker wrote: > > > > rcu/stall: Stall detection updates. Introduce RCU CPU Stall notifiers > > that allows a subsystem to provide informations to help debugging. > > Also cure some false positive stalls. > > I absolutely detest this stall notifier thing. > > Putting the stall notifier before the stall message does not "help > debugging". Quite the reverse. It ends up being a lovely way to make > sure that the debug message is never printed, because there's some > entirely untested - and thus buggy - notifier on the chain before the > printout from the actual stall code. > > I've pulled this, but I really want to voice my objection against > these kinds of "debugging aids". I have personally spent way too many > hours debugging a dead machine because some "debug aid" ended up being > untested garbage. > > If you absolutely think that this is a worthy and useful thing to do, > then at the very least make sure that these "debug aids" will always > come *after* the core output, and can't make things horrendously > worse. > > But in general, think twice before adding "maybe somebody else wants > to print debug info". Because unless you have a really really REALLY > good reason for it, it's more likely to hurt than to help. > > Right now I see no users of this except for the rcu torture code, and > it certainly doesn't seem hugely important there. And so I'm wondering > what the actual real use-case would be. I see, one possibility is to revert this and switch to normal calls for any future debug information to add from another subsystem. I'll wait for Paul's opinion... Thanks.