Re: [PATCH] serial: core: Fix atomicity violation in uart_tiocmget

[Gui-Dong Han <2045gemini@xxxxxxxxx>]

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