From patchwork Wed Apr 21 09:54:51 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Johan Hovold X-Patchwork-Id: 425684 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=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 39676C43470 for ; Wed, 21 Apr 2021 09:55:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 079836008E for ; Wed, 21 Apr 2021 09:55:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236658AbhDUJ4O (ORCPT ); Wed, 21 Apr 2021 05:56:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:52442 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238601AbhDUJ4J (ORCPT ); Wed, 21 Apr 2021 05:56:09 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2834D61440; Wed, 21 Apr 2021 09:55:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1618998936; bh=aru/Ih0Av7GxzcZcazb+Ui9kYy6sVxdsNzB3eD0DMVU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=StWhLcMAqMUJ8fHHL5DcwDmNGq/ksYveAqWKnvBEj9MPYPPVHXBWvL3Q2VeLOcGTv CMd++XaVrW1qbZP8AXHuZkqEsOuBTTYj8oqMpx4fYjbbaKMamn2Mror9+FTViL040f PTN72rr8dqZR9gs+8xjDd7bhJRT+YNoUJTBwUXFtsU/u0Ryzxp/HOSm8h4P+3dJILj sYdx5NVU0q6rKGeq3c21pJuFMzOZbJVsW2y5Fo+xZxJ0BruFiVLZSwraZTA1xy8nsn 11aMZvByRtOrkMABdHzgRUlYQiVxSsq9TNyV6sJZwQDxIF1NYAkKaUEgGjONtzUv1G z8n8eCqfLJ0Ew== Received: from johan by xi.lan with local (Exim 4.93.0.4) (envelope-from ) id 1lZ9a7-0000oh-Ca; Wed, 21 Apr 2021 11:55:39 +0200 From: Johan Hovold To: Greg Kroah-Hartman Cc: Jiri Slaby , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Johan Hovold , Vineet Gupta Subject: [PATCH 08/26] serial: arc_uart: drop low-latency workaround Date: Wed, 21 Apr 2021 11:54:51 +0200 Message-Id: <20210421095509.3024-9-johan@kernel.org> X-Mailer: git-send-email 2.26.3 In-Reply-To: <20210421095509.3024-1-johan@kernel.org> References: <20210421095509.3024-1-johan@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Commit 3fa1200851c7 ("tty: serial: arc: drop uart_port->lock before calling tty_flip_buffer_push()") claimed to address a locking issue but only provided a dubious lockdep splat from an unrelated driver, which in the end turned out to be due a broken local change carried by the author. Unfortunately these patches were merged before the issue had been analysed properly so the commit messages makes no sense whatsoever. The real issue was first seen on RT which at the time effectively always set the low_latency flag for all serial drivers by patching tty_flip_buffer_push(). This in turn revealed that many drivers did not handle the infamous low_latency behaviour which meant that data was pushed immediately to the line discipline instead of being deferred to a work queue. Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"), tty_flip_buffer_push() always schedules a work item to push data to the line discipline and there's no need to keep any low_latency hacks around. Link: https://lore.kernel.org/linux-serial/cover.1376923198.git.viresh.kumar@linaro.org/ Cc: Vineet Gupta Signed-off-by: Johan Hovold --- drivers/tty/serial/arc_uart.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/drivers/tty/serial/arc_uart.c b/drivers/tty/serial/arc_uart.c index 17c3fc398fc6..1a9444b6b57e 100644 --- a/drivers/tty/serial/arc_uart.c +++ b/drivers/tty/serial/arc_uart.c @@ -236,9 +236,7 @@ static void arc_serial_rx_chars(struct uart_port *port, unsigned int status) if (!(uart_handle_sysrq_char(port, ch))) uart_insert_char(port, status, RXOERR, ch, flg); - spin_unlock(&port->lock); tty_flip_buffer_push(&port->state->port); - spin_lock(&port->lock); } while (!((status = UART_GET_STATUS(port)) & RXEMPTY)); }