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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 37483C433C1 for ; Mon, 22 Mar 2021 19:02:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0852861998 for ; Mon, 22 Mar 2021 19:02:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232453AbhCVTCM (ORCPT ); Mon, 22 Mar 2021 15:02:12 -0400 Received: from netrider.rowland.org ([192.131.102.5]:47893 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S232372AbhCVTBa (ORCPT ); Mon, 22 Mar 2021 15:01:30 -0400 Received: (qmail 678067 invoked by uid 1000); 22 Mar 2021 15:01:25 -0400 Date: Mon, 22 Mar 2021 15:01:25 -0400 From: Alan Stern To: Sebastian Andrzej Siewior Cc: Johan Hovold , Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Stanislaw Gruszka , Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH] USB: ehci: drop workaround for forced irq threading Message-ID: <20210322190125.GD675969@rowland.harvard.edu> References: <20210322111249.32141-1-johan@kernel.org> <20210322164200.GB667925@rowland.harvard.edu> <20210322165917.it5d5f5kuvs7jah5@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210322165917.it5d5f5kuvs7jah5@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 22, 2021 at 05:59:17PM +0100, Sebastian Andrzej Siewior wrote: > On 2021-03-22 12:42:00 [-0400], Alan Stern wrote: > > What happens on RT systems? Are they smart enough to avoid the whole > > problem by enabling interrupts during _all_ callbacks? > > tl;dr: Yes. > > The referenced commit (id 81e2073c175b) disables interrupts only on !RT > configs so for RT everything remains unchanged (the backports are > already adjusted for the old stable trees to use the proper CONFIG_* for > enabled RT). > > All hrtimer callbacks run as HRTIMER_MODE_SOFT by default. The > HRTIMER_MODE_HARD ones (which expire in HARDIRQ context) were audited / > explicitly enabled. > The same goes irq_work. > The printk code is different compared to mainline. A printk() on RT in > HARDIRQ context is printed once the HARDIRQ context is left. So the > serial/console/… driver never gets a chance to acquire its lock in > hardirq context. > > An interrupt handler which is not forced-threaded must be marked as such > and must not use any spinlock_t based locking. lockdep/might_sleep > complain here already. Okay, in that case: Acked-by: Alan Stern