Re: [PATCH] tty: nozomi: lock tty_icount reads against the IRQ update path

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Sep 20, 2026 at 12:23:49AM +0500, Muhammad Bilal wrote:
> receive_flow_control() updates port->tty_icount.{cts,dsr,rng,dcd}
> while interrupt_handler() holds dc->spin_mutex, but ntty_tiocgicount()
> and the TIOCMIWAIT snapshot/compare loop in ntty_ioctl()/
> ntty_cflags_changed() read the same multi-field struct with no lock
> at all. A concurrent update can be observed mid-copy, and KCSAN flags
> the unlocked access.
> 
> Add ntty_get_icount() to snapshot port->tty_icount under
> dc->spin_mutex and use it at all three read sites, matching the lock
> already used on the update side.
> 
> Fixes: 20fd1e3bea55 ("nozomi driver")
> Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
> ---
>  drivers/tty/nozomi.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)

You forgot an Assisted-by: tag, right?

And how did you test this?


> 
> diff --git a/drivers/tty/nozomi.c b/drivers/tty/nozomi.c
> index ed99dbc9f990..4b2e224c0aa2 100644
> --- a/drivers/tty/nozomi.c
> +++ b/drivers/tty/nozomi.c
> @@ -1671,10 +1671,23 @@ static int ntty_tiocmset(struct tty_struct *tty,
>  	return 0;
>  }
>  
> +static struct async_icount ntty_get_icount(struct port *port)
> +{
> +	struct nozomi *dc = port->dc;
> +	struct async_icount cnow;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&dc->spin_mutex, flags);
> +	cnow = port->tty_icount;
> +	spin_unlock_irqrestore(&dc->spin_mutex, flags);
> +
> +	return cnow;

This is text-book LLM-written code as they do not know how to write
"modern" Linux kernel code.  Please fix.

thanks,

greg k-h