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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7599C433E2 for ; Mon, 14 Sep 2020 19:00:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7683220759 for ; Mon, 14 Sep 2020 19:00:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725994AbgINTAy (ORCPT ); Mon, 14 Sep 2020 15:00:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:33216 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725951AbgINTAx (ORCPT ); Mon, 14 Sep 2020 15:00:53 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6C053206B2; Mon, 14 Sep 2020 19:00:51 +0000 (UTC) Date: Mon, 14 Sep 2020 15:00:49 -0400 From: Steven Rostedt To: peterz@infradead.org Cc: Andrew Morton , Joerg Vehlow , Thomas Gleixner , Sebastian Andrzej Siewior , Huang Ying , linux-kernel@vger.kernel.org, Joerg Vehlow , dave@stgolabs.net Subject: Re: [BUG RT] dump-capture kernel not executed for panic in interrupt context Message-ID: <20200914150049.309e985c@gandalf.local.home> In-Reply-To: <20200907114140.GQ2674@hirez.programming.kicks-ass.net> References: <2c243f59-6d10-7abb-bab4-e7b1796cd54f@jv-coder.de> <20200528084614.0c949e8d@gandalf.local.home> <20200727163655.8c94c8e245637b62311f5053@linux-foundation.org> <20200821110848.6c3183d1@oasis.local.home> <20200821134753.9547695c9b782275be3c95b5@linux-foundation.org> <20200821170334.73b52fdd@oasis.local.home> <20200822123252.GQ1362448@hirez.programming.kicks-ass.net> <20200822194928.54ee4cb5@oasis.local.home> <20200907114140.GQ2674@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 7 Sep 2020 13:41:40 +0200 peterz@infradead.org wrote: > > I may have once known the rationale behind all this, but it's been a > > long time since I worked on the PI code, and it's out of my cache. Now I'm trying to cache all this in from a long PTO ;-) > > I suffer much the same problem. > > So cenceptually there's the problem that idle must always be runnable, > and the moment you boost it, it becomes subject to a different > scheduling class. > > Imagine for example what happens when we boost it to RT and then have it > be subject to throttling. What are we going to run when the idle task > is no longer elegible to run. > > (it might all work out by accident, but ISTR we had a whole bunch of fun > in the earlier days of RT due to things like that) I'm thinking if a mutex_trylock() happens in an interrupt context, which I believe is the only way idle could trigger it, it could not be throttled if boosted, because it's in interrupt context. And it would have to release the mutex before leaving interrupt context putting it back to the idle state before throttling could take effect. Thus, I'm still not convinced that mutex_trylock() is still bad in interrupt context yet. At least not from what I can tell. -- Steve