From patchwork Mon Apr 6 21:22:17 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Ogness X-Patchwork-Id: 213166 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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 F36E5C2BA1A for ; Mon, 6 Apr 2020 21:22:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8CEC2072A for ; Mon, 6 Apr 2020 21:22:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726395AbgDFVWa (ORCPT ); Mon, 6 Apr 2020 17:22:30 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:45709 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726130AbgDFVWa (ORCPT ); Mon, 6 Apr 2020 17:22:30 -0400 Received: from [5.158.153.53] (helo=nereus.lab.linutronix.de.) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1jLZCM-00013T-Sd; Mon, 06 Apr 2020 23:22:27 +0200 From: John Ogness To: Sebastian Andrzej Siewior Cc: Petr Mladek , Sergey Senozhatsky , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org Subject: [PATCH RT] printk: console must not schedule for drivers Date: Mon, 6 Apr 2020 23:22:17 +0200 Message-Id: <20200406212217.2323-1-john.ogness@linutronix.de> X-Mailer: git-send-email 2.19.0 MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1, SHORTCIRCUIT=-0.0001 Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org 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. Reported-by: kernel test robot Signed-off-by: John Ogness --- kernel/printk/printk.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 8821a8c2263f..8bc683be0857 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2715,6 +2715,7 @@ static int printk_kthread_func(void *data) &len, printk_time); console_lock(); + console_may_schedule = 0; call_console_drivers(master_seq, ext_text, ext_len, text, len, msg->level, msg->facility); if (len > 0 || ext_len > 0)