From patchwork Thu Sep 21 14:52:33 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lukas Wunner X-Patchwork-Id: 725169 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 13A73E7D0A2 for ; Thu, 21 Sep 2023 18:38:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229513AbjIUSih (ORCPT ); Thu, 21 Sep 2023 14:38:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229533AbjIUSiJ (ORCPT ); Thu, 21 Sep 2023 14:38:09 -0400 X-Greylist: delayed 4199 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Thu, 21 Sep 2023 11:31:08 PDT Received: from mailout3.hostsharing.net (mailout3.hostsharing.net [176.9.242.54]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAF5ED9D31 for ; Thu, 21 Sep 2023 11:31:08 -0700 (PDT) Received: from h08.hostsharing.net (h08.hostsharing.net [83.223.95.28]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL Global TLS RSA4096 SHA256 2022 CA1" (verified OK)) by mailout3.hostsharing.net (Postfix) with ESMTPS id F3415102CCA20; Thu, 21 Sep 2023 16:53:09 +0200 (CEST) Received: from localhost (unknown [89.246.108.87]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by h08.hostsharing.net (Postfix) with ESMTPSA id A5D6060DC7CD; Thu, 21 Sep 2023 16:53:09 +0200 (CEST) X-Mailbox-Line: From f3a35967c28b32f3c6432d0aa5936e6a9908282d Mon Sep 17 00:00:00 2001 Message-Id: From: Lukas Wunner Date: Thu, 21 Sep 2023 16:52:33 +0200 Subject: [PATCH tty-linus] serial: Reduce spinlocked portion of uart_rs485_config() To: Greg Kroah-Hartman Cc: Jiri Slaby , Ilpo Jarvinen , John Ogness , Lino Sanfilippo , linux-serial@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Commit 44b27aec9d96 ("serial: core, 8250: set RS485 termination GPIO in serial core") enabled support for RS485 termination GPIOs behind i2c expanders by setting the GPIO outside of the critical section protected by the port spinlock. Access to the i2c expander may sleep, which caused a splat with the port spinlock held. Commit 7c7f9bc986e6 ("serial: Deassert Transmit Enable on probe in driver-specific way") erroneously regressed that by spinlocking the GPIO manipulation again. Fix by moving uart_rs485_config() (the function manipulating the GPIO) outside of the spinlocked section and acquiring the spinlock inside of uart_rs485_config() for the invocation of ->rs485_config() only. This gets us one step closer to pushing the spinlock down into the ->rs485_config() callbacks which actually need it. (Some callbacks do not want to be spinlocked because they perform sleepable register accesses, see e.g. sc16is7xx_config_rs485().) Stack trace for posterity: Voluntary context switch within RCU read-side critical section! WARNING: CPU: 0 PID: 56 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch Call trace: rcu_note_context_switch __schedule schedule schedule_timeout wait_for_completion_timeout bcm2835_i2c_xfer __i2c_transfer i2c_transfer i2c_transfer_buffer_flags regmap_i2c_write _regmap_raw_write_impl _regmap_bus_raw_write _regmap_write _regmap_update_bits regmap_update_bits_base pca953x_gpio_set_value gpiod_set_raw_value_commit gpiod_set_value_nocheck gpiod_set_value_cansleep uart_rs485_config uart_add_one_port pl011_register_port pl011_probe Fixes: 7c7f9bc986e6 ("serial: Deassert Transmit Enable on probe in driver-specific way") Suggested-by: Lino Sanfilippo Signed-off-by: Lukas Wunner Cc: stable@vger.kernel.org # v6.1+ --- drivers/tty/serial/serial_core.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 7bdc21d5e13b..ca26a8aef2cb 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1404,12 +1404,18 @@ static void uart_set_rs485_termination(struct uart_port *port, static int uart_rs485_config(struct uart_port *port) { struct serial_rs485 *rs485 = &port->rs485; + unsigned long flags; int ret; + if (!(rs485->flags & SER_RS485_ENABLED)) + return 0; + uart_sanitize_serial_rs485(port, rs485); uart_set_rs485_termination(port, rs485); + spin_lock_irqsave(&port->lock, flags); ret = port->rs485_config(port, NULL, rs485); + spin_unlock_irqrestore(&port->lock, flags); if (ret) memset(rs485, 0, sizeof(*rs485)); @@ -2474,11 +2480,10 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport) if (ret == 0) { if (tty) uart_change_line_settings(tty, state, NULL); + uart_rs485_config(uport); spin_lock_irq(&uport->lock); if (!(uport->rs485.flags & SER_RS485_ENABLED)) ops->set_mctrl(uport, uport->mctrl); - else - uart_rs485_config(uport); ops->start_tx(uport); spin_unlock_irq(&uport->lock); tty_port_set_initialized(port, true); @@ -2587,10 +2592,10 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state, port->mctrl &= TIOCM_DTR; if (!(port->rs485.flags & SER_RS485_ENABLED)) port->ops->set_mctrl(port, port->mctrl); - else - uart_rs485_config(port); spin_unlock_irqrestore(&port->lock, flags); + uart_rs485_config(port); + /* * If this driver supports console, and it hasn't been * successfully registered yet, try to re-register it.