Re: [PATCH V2 11/11] arch: xtensa: platforms: Fix deadlock in rs_close()

[Max Filippov]

On Thu, Apr 7, 2022 at 8:44 AM Duoming Zhou <duoming@xxxxxxxxxx> wrote:
>
> There is a deadlock in rs_close(), which is shown
> below:
>
>    (Thread 1)              |      (Thread 2)
>                            | rs_open()
> rs_close()                 |  mod_timer()
>  spin_lock_bh() //(1)      |  (wait a time)
>  ...                       | rs_poll()
>  del_timer_sync()          |  spin_lock() //(2)
>  (wait timer to stop)      |  ...
>
> We hold timer_lock in position (1) of thread 1 and
> use del_timer_sync() to wait timer to stop, but timer handler
> also need timer_lock in position (2) of thread 2.
> As a result, rs_close() will block forever.
>
> This patch deletes the redundant timer_lock in order to
> prevent the deadlock. Because there is no race condition
> between rs_close, rs_open and rs_poll.
>
> Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
> ---
> Changes in V2:
>   - Remove the timer_lock.
>
>  arch/xtensa/platforms/iss/console.c | 8 --------
>  1 file changed, 8 deletions(-)

Thanks. Applied to my xtensa tree.

-- Max