Re: [PATCH 07/24] serial: 8250: hold hash_mutex across irq_info lookup and linking

[Ilpo Järvinen]

On Tue, 27 Oct 2026, Greg Kroah-Hartman wrote:

> From: Joshua Rogers <linux@xxxxxxxxx>
> 
> serial_get_or_create_irq_info() released hash_mutex before returning the
> irq_info pointer, allowing serial_unlink_irq_chain() on another CPU to
> free the irq_info before serial_link_irq_chain() could link its port,
> causing a use-after-free. Hold hash_mutex in serial_link_irq_chain() for
> its entire scope so the irq_info lifetime is protected across both
> lookup and linking.
> 
> Cc: stable <stable@xxxxxxxxxx>
> Cc: Jiri Slaby <jirislaby@xxxxxxxxxx>
> Cc: John Ogness <john.ogness@xxxxxxxxxxxxx>
> Cc: Fushuai Wang <wangfushuai@xxxxxxxxx>
> Cc: Crescent Hsieh <crescentcy.hsieh@xxxxxxxx>
> Cc: "Uwe Kleine-König (The Capable Hub)" <u.kleine-koenig@xxxxxxxxxxxx>
> Signed-off-by: Joshua Rogers <linux@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/tty/serial/8250/8250_core.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 673fde55828a..5730ef97f836 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -131,12 +131,11 @@ static void serial_do_unlink(struct irq_info *i, struct uart_8250_port *up)
>   * - find the corresponding info in the hashtable and return it, or
>   * - allocate a new one, add it to the hashtable and return it.
>   */
> +/* Caller must hold hash_mutex */

We do have lockdep asserts to actually check these.

I also don't understand why own comment is opened for this. And it would 
be better to follow kerneldoc's syntax by starting with Context:

>  static struct irq_info *serial_get_or_create_irq_info(const struct uart_8250_port *up)
>  {
>  	struct irq_info *i;
>  
> -	guard(mutex)(&hash_mutex);
> -
>  	hash_for_each_possible(irq_lists, i, node, up->port.irq)
>  		if (i->irq == up->port.irq)
>  			return i;
> @@ -157,6 +156,8 @@ static int serial_link_irq_chain(struct uart_8250_port *up)
>  	struct irq_info *i;
>  	int ret;
>  
> +	guard(mutex)(&hash_mutex);
> +
>  	i = serial_get_or_create_irq_info(up);
>  	if (IS_ERR(i))
>  		return PTR_ERR(i);
> 
> 

-- 
 i.