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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 91F7AC433EF for ; Mon, 24 Jan 2022 19:03:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345460AbiAXTDl (ORCPT ); Mon, 24 Jan 2022 14:03:41 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:56362 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344839AbiAXS7U (ORCPT ); Mon, 24 Jan 2022 13:59:20 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 357ED608D4; Mon, 24 Jan 2022 18:59:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1149C340E7; Mon, 24 Jan 2022 18:59:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643050759; bh=JcvhSTU1IQqq+oYId9prgK7Cki2I3kfKY0v6RsGm2zU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZZRCyZTDZyPus2+l4q0LdJRch7rrwToPzmfdrchKkx/NsSdfTlSMdLQF/BawoYX8a 78FylcI1c47+0HY0hSsCRTaC3ztSh4zN+vYf/UKxh6hRkGW3ZNVBI1n63z6ONdxhCN NoIbIxqzJVm8rMtd9dTd/t3lX7NhyLH4ECZvBlPw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Lukas Wunner , Sasha Levin Subject: [PATCH 4.9 103/157] serial: core: Keep mctrl register state and cached copy in sync Date: Mon, 24 Jan 2022 19:43:13 +0100 Message-Id: <20220124183936.032114999@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124183932.787526760@linuxfoundation.org> References: <20220124183932.787526760@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lukas Wunner [ Upstream commit 93a770b7e16772530196674ffc79bb13fa927dc6 ] struct uart_port contains a cached copy of the Modem Control signals. It is used to skip register writes in uart_update_mctrl() if the new signal state equals the old signal state. It also avoids a register read to obtain the current state of output signals. When a uart_port is registered, uart_configure_port() changes signal state but neglects to keep the cached copy in sync. That may cause a subsequent register write to be incorrectly skipped. Fix it before it trips somebody up. This behavior has been present ever since the serial core was introduced in 2002: https://git.kernel.org/history/history/c/33c0d1b0c3eb So far it was never an issue because the cached copy is initialized to 0 by kzalloc() and when uart_configure_port() is executed, at most DTR has been set by uart_set_options() or sunsu_console_setup(). Therefore, a stable designation seems unnecessary. Signed-off-by: Lukas Wunner Link: https://lore.kernel.org/r/bceeaba030b028ed810272d55d5fc6f3656ddddb.1641129752.git.lukas@wunner.de Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/serial_core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index e97961dc3622d..ec458add38833 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -2349,7 +2349,8 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state, * We probably don't need a spinlock around this, but */ spin_lock_irqsave(&port->lock, flags); - port->ops->set_mctrl(port, port->mctrl & TIOCM_DTR); + port->mctrl &= TIOCM_DTR; + port->ops->set_mctrl(port, port->mctrl); spin_unlock_irqrestore(&port->lock, flags); /* -- 2.34.1