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SubjectRe: [PATCH] staging: greybus: fix a possible data-inconsistency due to data race in get_serial_info()
On Mon, Jun 26, 2023 at 04:43:39PM +0800, Tuo Li wrote:
> The variables gb_tty->port.close_delay and gb_tty->port.closing_wait are
> ofter accessed together while holding the lock gb_tty->port.mutex. Here is
> an example in set_serial_info():
>
> mutex_lock(&gb_tty->port.mutex);
> ...
> gb_tty->port.close_delay = close_delay;
> gb_tty->port.closing_wait = closing_wait;
> ...
> mutex_unlock(&gb_tty->port.mutex);
>
> However, they are accessed without holding the lock gb_tty->port.mutex when
> are accessed in get_serial_info():
>
> ss->close_delay = jiffies_to_msecs(gb_tty->port.close_delay) / 10;
> ss->closing_wait =
> gb_tty->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ?
> ASYNC_CLOSING_WAIT_NONE :
> jiffies_to_msecs(gb_tty->port.closing_wait) / 10;
>
> In my opinion, this may be a harmful race, because ss->close_delay can be
> inconsistent with ss->closing_wait if gb_tty->port.close_delay and
> gb_tty->port.closing_wait are updated by another thread after the
> assignment to ss->close_delay.

And how can that happen?

Also you have trailing whitespace in your changelog text :(

> Besides, the select operator may return wrong value if
> gb_tty->port.closing_wait is updated right after the condition is
> calculated.
>
> To fix this possible data-inconsistency caused by data race, a lock and
> unlock pair is added when accessing different fields of gb_tty->port.
>
> Reported-by: BassCheck <bass@buaa.edu.cn>

As per the documentation for research tools like this, you need to
explain how this was tested.

thanks,

greg k-h

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