On Wed, Apr 14, 2021 at 12:17:54AM +0000, Gong, Sishuai wrote:
> Hi,
>
> We found a data race between two tty functions tty_port_open() and uart_do_autoconfig() in linux-5.12-rc3 and we are able to reproduce it under x86. In general, when tty_port_open() and uart_do_autoconfig() are running in parallel, uart_do_autoconfig() may fetch an out-of-date value of port->count and enter into a different execution path, as shown below.
>
> Currently, we haven’t found any explicit errors due to this data race but we noticed the developer has used lock to read port->count, so we want to point out this data race in case this is unexpected.
>
> ------------------------------------------
> Execution interleaving
>
> Thread 1 Thread 2
> tty_port_open() uart_do_autoconfig()
>
> spin_lock_irq(&port->lock);
> if (mutex_lock_interruptible(&port->mutex))
> …
> if (tty_port_users(port) == 1) {
> uart_shutdown(tty, state);
>
> ++port->count;
> spin_unlock_irq(&port->lock);
>
>
>
Can you send a proposed patch for this to fix the issue as you sem to
have a reproducer for this that you can test if the change resolves the
issue or not?
thanks,
greg k-h
