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Date: Fri, 12 Jan 2024 19:23:17 +0800
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Subject: Re: [PATCH] serial: core: Fix atomicity violation in uart_tiocmget
To: =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>,
 John Ogness <john.ogness@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Jiri Slaby <jirislaby@kernel.org>, Tony Lindgren <tony@atomide.com>,
 l.sanfilippo@kunbus.com, tglx@linutronix.de,
 Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
 LKML <linux-kernel@vger.kernel.org>,
 linux-serial <linux-serial@vger.kernel.org>, baijiaju1990@outlook.com,
 stable@vger.kernel.org
References: <20240112075732.16730-1-2045gemini@gmail.com>
 <87msta7vbe.fsf@jogness.linutronix.de>
 <4a52df23-71c3-59c7-fee4-e7cde526d249@linux.intel.com>
From: Gui-Dong Han <2045gemini@gmail.com>
In-Reply-To: <4a52df23-71c3-59c7-fee4-e7cde526d249@linux.intel.com>
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Hi,

You are correct about the 'Fixes' tag. It should indeed be c5f4644e6c8b 
("[PATCH] Serial: Adjust serial locking"). I will update this in the 
patch v2.


Regarding the issue found in Linux 5.17, I mistakenly used git blame 
which led to the incorrect identification of commit 559c7ff4e324. The 
issue indeed exists in Linux 5.17 and I acknowledge the error in tracing 
the commit.

In uart_tiocmget(), the result variable is stable. However, there's a 
risk of inconsistency due to the updates in uart_update_mctrl(). 
Consider a scenario where uart_tiocmget() reads uport->mctrl into result 
before entering the critical section. If uart_update_mctrl() updates 
port->mctrl and calls set_mctrl concurrently, the subsequent execution 
of result |= uport->ops->get_mctrl(uport); in uart_tiocmget() might 
yield an inaccurate result. This happens because result contains the old 
value of port->mctrl, which no longer matches the updated state 
retrieved by get_mctrl.

Thanks,

Han