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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 2C4CDC432C0 for ; Fri, 22 Nov 2019 06:11:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 048D32068E for ; Fri, 22 Nov 2019 06:11:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574403087; bh=yswybrNRsWsvoHS/VoCxngFKHac2PIA2wYGZakRfmRY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=s99e7oOUkBUHY+Dhfwf1NbkSdXnpv14TI6eSY24v9LBVvd+gn3p0UdJj4qDg0s+2P AOYb8SQsMgCxtzYT8MtY3haNJobYF64/I5wS0rtbF9YAIuo7JztkF1BnO+OoHbJ2Rd lPnZim+EmVOC7iADzCLUaNT+6BRruR7CNmyWY2D0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729174AbfKVF4d (ORCPT ); Fri, 22 Nov 2019 00:56:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:34154 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729122AbfKVF4X (ORCPT ); Fri, 22 Nov 2019 00:56:23 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B4A982072D; Fri, 22 Nov 2019 05:56:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574402182; bh=yswybrNRsWsvoHS/VoCxngFKHac2PIA2wYGZakRfmRY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=t+q+2/Glb6WU8ZwFmsNg6I5xhV4s9ySSqyHWo/FTXSizJQYC29G3EW0Wc6XYPKeX4 58vWNq37wQdFdSwiHZn5qVqsPsGSKO836PUTRdV4KXE5GZOIoDWG5/LCLAAYIK3NBv jbtNzHQ6Cg0NClDmhLw1DARYURFEE0gyADeIIm0U= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Darwin Dingel , Greg Kroah-Hartman , Sasha Levin , linux-serial@vger.kernel.org Subject: [PATCH AUTOSEL 4.14 033/127] serial: 8250: Rate limit serial port rx interrupts during input overruns Date: Fri, 22 Nov 2019 00:54:11 -0500 Message-Id: <20191122055544.3299-32-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191122055544.3299-1-sashal@kernel.org> References: <20191122055544.3299-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Darwin Dingel [ Upstream commit 6d7f677a2afa1c82d7fc7af7f9159cbffd5dc010 ] When a serial port gets faulty or gets flooded with inputs, its interrupt handler starts to work double time to get the characters to the workqueue for the tty layer to handle them. When this busy time on the serial/tty subsystem happens during boot, where it is also busy on the userspace trying to initialise, some processes can continuously get preempted and will be on hold until the interrupts subside. The fix is to backoff on processing received characters for a specified amount of time when an input overrun is seen (received a new character before the previous one is processed). This only stops receive and will continue to transmit characters to serial port. After the backoff period is done, it receive will be re-enabled. This is optional and will only be enabled by setting 'overrun-throttle-ms' in the dts. Signed-off-by: Darwin Dingel Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/8250/8250_core.c | 25 +++++++++++++++++++++++++ drivers/tty/serial/8250/8250_fsl.c | 23 ++++++++++++++++++++++- drivers/tty/serial/8250/8250_of.c | 5 +++++ include/linux/serial_8250.h | 4 ++++ 4 files changed, 56 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index d29b512a7d9fa..ceeea4b159c4b 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -953,6 +953,21 @@ static struct uart_8250_port *serial8250_find_match_or_unused(struct uart_port * return NULL; } +static void serial_8250_overrun_backoff_work(struct work_struct *work) +{ + struct uart_8250_port *up = + container_of(to_delayed_work(work), struct uart_8250_port, + overrun_backoff); + struct uart_port *port = &up->port; + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + up->ier |= UART_IER_RLSI | UART_IER_RDI; + up->port.read_status_mask |= UART_LSR_DR; + serial_out(up, UART_IER, up->ier); + spin_unlock_irqrestore(&port->lock, flags); +} + /** * serial8250_register_8250_port - register a serial port * @up: serial port template @@ -1063,6 +1078,16 @@ int serial8250_register_8250_port(struct uart_8250_port *up) ret = 0; } } + + /* Initialise interrupt backoff work if required */ + if (up->overrun_backoff_time_ms > 0) { + uart->overrun_backoff_time_ms = up->overrun_backoff_time_ms; + INIT_DELAYED_WORK(&uart->overrun_backoff, + serial_8250_overrun_backoff_work); + } else { + uart->overrun_backoff_time_ms = 0; + } + mutex_unlock(&serial_mutex); return ret; diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c index 910bfee5a88b7..cc138c24ae889 100644 --- a/drivers/tty/serial/8250/8250_fsl.c +++ b/drivers/tty/serial/8250/8250_fsl.c @@ -48,8 +48,29 @@ int fsl8250_handle_irq(struct uart_port *port) lsr = orig_lsr = up->port.serial_in(&up->port, UART_LSR); - if (lsr & (UART_LSR_DR | UART_LSR_BI)) + /* Process incoming characters first */ + if ((lsr & (UART_LSR_DR | UART_LSR_BI)) && + (up->ier & (UART_IER_RLSI | UART_IER_RDI))) { lsr = serial8250_rx_chars(up, lsr); + } + + /* Stop processing interrupts on input overrun */ + if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) { + unsigned long delay; + + up->ier = port->serial_in(port, UART_IER); + if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) { + port->ops->stop_rx(port); + } else { + /* Keep restarting the timer until + * the input overrun subsides. + */ + cancel_delayed_work(&up->overrun_backoff); + } + + delay = msecs_to_jiffies(up->overrun_backoff_time_ms); + schedule_delayed_work(&up->overrun_backoff, delay); + } serial8250_modem_status(up); diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c index ec510e342e06c..c51044ba503c3 100644 --- a/drivers/tty/serial/8250/8250_of.c +++ b/drivers/tty/serial/8250/8250_of.c @@ -232,6 +232,11 @@ static int of_platform_serial_probe(struct platform_device *ofdev) if (of_property_read_bool(ofdev->dev.of_node, "auto-flow-control")) port8250.capabilities |= UART_CAP_AFE; + if (of_property_read_u32(ofdev->dev.of_node, + "overrun-throttle-ms", + &port8250.overrun_backoff_time_ms) != 0) + port8250.overrun_backoff_time_ms = 0; + ret = serial8250_register_8250_port(&port8250); if (ret < 0) goto err_dispose; diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index a27ef5f564317..791a6be0e3949 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -134,6 +134,10 @@ struct uart_8250_port { void (*dl_write)(struct uart_8250_port *, int); struct uart_8250_em485 *em485; + + /* Serial port overrun backoff */ + struct delayed_work overrun_backoff; + u32 overrun_backoff_time_ms; }; static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up) -- 2.20.1