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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E658DC2BA19 for ; Wed, 15 Apr 2020 16:34:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C5A172051A for ; Wed, 15 Apr 2020 16:34:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1416152AbgDOQeX (ORCPT ); Wed, 15 Apr 2020 12:34:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58362 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1416090AbgDOQeT (ORCPT ); Wed, 15 Apr 2020 12:34:19 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 80F90C061A0C; Wed, 15 Apr 2020 09:34:19 -0700 (PDT) Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1jOkzQ-0006Uc-V3; Wed, 15 Apr 2020 18:34:17 +0200 Date: Wed, 15 Apr 2020 18:34:16 +0200 From: Sebastian Andrzej Siewior To: John Ogness Cc: Petr Mladek , Sergey Senozhatsky , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org Subject: Re: [PATCH RT] printk: console must not schedule for drivers Message-ID: <20200415163416.r3fce3g5kokm4bub@linutronix.de> References: <20200406212217.2323-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200406212217.2323-1-john.ogness@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-04-06 23:22:17 [+0200], John Ogness wrote: > Even though the printk kthread is always preemptible, it is still not > allowed to call cond_resched() from within console drivers. The > task may become non-preemptible in the console driver call chain. For > example, vt_console_print() takes a spinlock and then can call into > fbcon_redraw(), which can conditionally invoke cond_resched(): > > BUG: sleeping function called from invalid context at kernel/printk/printk.c:2322 > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 177, name: printk > CPU: 0 PID: 177 Comm: printk Not tainted 5.6.2-00011-ga536059557f1d9 #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 > Call Trace: > dump_stack+0x66/0x8b > ___might_sleep+0x102/0x120 > console_conditional_schedule+0x24/0x30 > fbcon_redraw+0x96/0x1c0 > ? fbcon_cursor+0x100/0x190 > fbcon_scroll+0x556/0xd70 > con_scroll+0x147/0x1e0 > lf+0x9e/0xb0 > vt_console_print+0x253/0x3d0 > printk_kthread_func+0x1d5/0x3b0 > > Disable cond_resched() for the call into the console drivers. Interesting. So you get a report and I don't? I have also patch related questions :) - So before the re-rewrite, console_unlock() set this 0 before invoking the console drivers so it was always 0. I assume it was called with disabled interrupts. - Is there a scenario in fbcon where this function is invoked and console_may_schedule is not 0? Sebastian