On Wed, 23 Sep 2020 at 16:19, Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> wrote: > > It has been discovered that there is a potential deadlock between > the clock-change-notifier thread and the UART port suspending one: > > CPU0 (suspend CPU/UART) CPU1 (update clock) > ---- ---- > lock(&port->mutex); > lock((work_completion)(&data->clk_work)); > lock(&port->mutex); > lock((work_completion)(&data->clk_work)); > > *** DEADLOCK *** > > The best way to fix this is to eliminate the CPU0 > port->mutex/work-completion scenario. So we suggest to register and > unregister the clock-notifier during the DW APB UART port probe/remove > procedures, instead of doing that at the points of the port > startup/shutdown. > > Link: https://lore.kernel.org/linux-serial/f1cd5c75-9cda-6896-a4e2-42c5bfc3f5c3@xxxxxxxxxx > > Fixes: cc816969d7b5 ("serial: 8250_dw: Fix common clocks usage race condition") > Reported-by: Hans de Goede <hdegoede@xxxxxxxxxx> > Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> Tested-by: Jonathan Liu <net147@xxxxxxxxx> Fixes hang while closing the serial port on RK3399 that I was experiencing often with Linux 5.9. After applying this patch, it no longer hangs while closing the serial port. No problems while rebooting either. Thanks. Regards, Jonathan
