From nobody Sun Apr 19 17:01:42 2026 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 F2258C433EF for ; Tue, 28 Jun 2022 16:59:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232953AbiF1Q7R (ORCPT ); Tue, 28 Jun 2022 12:59:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43792 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229600AbiF1Q7B (ORCPT ); Tue, 28 Jun 2022 12:59:01 -0400 Received: from mga06.intel.com (mga06b.intel.com [134.134.136.31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDDA0139; Tue, 28 Jun 2022 09:59:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1656435540; x=1687971540; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=ZMmJv0Aq1HwpnPUpXeTro+xXVdnw6ntT+2+Mu0JHFpA=; b=R7FNwhCwPsEWOn2V7Y72JBBh4Tlu6UgIZO4OLFOKg3IWF/FGc9YJWGRf s3VnIydYFrEBNATIsocqpVOQy+1M8drp0mKn6a72fi1FoJwobD2Gu3kak umCMRQgRByv8JMp0STpmPe9qyZid383PvN2/EJC/lB9NsPjaqgdJdkL3i XAzDY4KeEPmopmaE5YCnWb94XJ+DqFLSkm1OrI/vQc4buTmSXrx7dDCkw Jbp45nMXAe0T/L2/lg1hoanNivewMppHSgz/x62lno+hOXGGHDoKI3lc1 XbDpK1QO03yyIIn3wp4FC/rGSNNTUWGwFSR48/xOwNVWCsYhibvD3n4xt w==; X-IronPort-AV: E=McAfee;i="6400,9594,10392"; a="343485041" X-IronPort-AV: E=Sophos;i="5.92,229,1650956400"; d="scan'208";a="343485041" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jun 2022 09:58:51 -0700 X-IronPort-AV: E=Sophos;i="5.92,229,1650956400"; d="scan'208";a="646995337" Received: from iannetti-mobl.ger.corp.intel.com (HELO ijarvine-MOBL2.ger.corp.intel.com) ([10.251.216.215]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jun 2022 09:58:49 -0700 From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= To: Greg Kroah-Hartman , Jiri Slaby , Andy Shevchenko , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Tony Lindgren , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Subject: [PATCH] serial: 8250: Fix PM usage_count for console handover Date: Tue, 28 Jun 2022 19:58:34 +0300 Message-Id: <20220628165834.63044-1-ilpo.jarvinen@linux.intel.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When console is enabled, univ8250_console_setup() calls serial8250_console_setup() before .dev is set to uart_port. Therefore, it will not call pm_runtime_get_sync(). Later, when the actual driver is going to take over univ8250_console_exit() is called. As .dev is already set, serial8250_console_exit() makes pm_runtime_put_sync() call with usage count being zero triggering PM usage count warning (extra debug for univ8250_console_setup(), univ8250_console_exit(), and serial8250_register_ports()): [ 0.068987] univ8250_console_setup ttyS0 nodev [ 0.499670] printk: console [ttyS0] enabled [ 0.717955] printk: console [ttyS0] printing thread started [ 1.960163] serial8250_register_ports assigned dev for ttyS0 [ 1.976830] printk: console [ttyS0] disabled [ 1.976888] printk: console [ttyS0] printing thread stopped [ 1.977073] univ8250_console_exit ttyS0 usage:0 [ 1.977075] serial8250 serial8250: Runtime PM usage count underflow! [ 1.977429] dw-apb-uart.6: ttyS0 at MMIO 0x4010006000 (irq =3D 33, base_= baud =3D 115200) is a 16550A [ 1.977812] univ8250_console_setup ttyS0 usage:2 [ 1.978167] printk: console [ttyS0] printing thread started [ 1.978203] printk: console [ttyS0] enabled To fix the issue, call pm_runtime_get_sync() in serial8250_register_ports() as soon as .dev is set for an uart_port if it has console enabled. This problem became apparent only recently because 82586a721595 ("PM: runtime: Avoid device usage count underflows") added the warning printout. I confirmed this problem also occurs with v5.18 (w/o the warning printout, obviously) so the recent printk kthreads are not the cause for this. Fixes: bedb404e91bb ("serial: 8250_port: Don't use power management for ker= nel console") Signed-off-by: Ilpo J=C3=A4rvinen Reviewed-by: Andy Shevchenko Reviewed-by: Tony Lindgren Tested-by: Tony Lindgren --- drivers/tty/serial/8250/8250_core.c | 4 ++++ drivers/tty/serial/serial_core.c | 5 ----- include/linux/serial_core.h | 5 +++++ 3 files changed, 9 insertions(+), 5 deletions(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/= 8250_core.c index 57e86133af4f..2e83e7367441 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include #include @@ -558,6 +559,9 @@ serial8250_register_ports(struct uart_driver *drv, stru= ct device *dev) =20 up->port.dev =3D dev; =20 + if (uart_console_enabled(&up->port)) + pm_runtime_get_sync(up->port.dev); + serial8250_apply_quirks(up); uart_add_one_port(drv, &up->port); } diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_c= ore.c index 85ef7ef00b82..3161445504bc 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -2024,11 +2024,6 @@ static int uart_proc_show(struct seq_file *m, void *= v) } #endif =20 -static inline bool uart_console_enabled(struct uart_port *port) -{ - return uart_console(port) && (port->cons->flags & CON_ENABLED); -} - static void uart_port_spin_lock_init(struct uart_port *port) { spin_lock_init(&port->lock); diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index b7b86ee3cb12..9d8aa139b175 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -404,6 +404,11 @@ static const bool earlycon_acpi_spcr_enable EARLYCON_U= SED_OR_UNUSED; static inline int setup_earlycon(char *buf) { return 0; } #endif =20 +static inline bool uart_console_enabled(struct uart_port *port) +{ + return uart_console(port) && (port->cons->flags & CON_ENABLED); +} + struct uart_port *uart_get_console(struct uart_port *ports, int nr, struct console *c); int uart_parse_earlycon(char *p, unsigned char *iotype, resource_size_t *a= ddr, --=20 tg: (f287f971e256..) fix/console-usage_count (depends on: tty-next)