On Fri, Nov 20, 2020 at 07:25:03PM +0800, tiantao (H) wrote:
> 在 2020/11/20 16:23, Johan Hovold 写道:
> > On Thu, Nov 19, 2020 at 05:01:29PM +0800, Tian Tao wrote:
> >> The code has been in a irq-disabled context since it is hard IRQ. There
> >> is no necessity to do it again.
> >>
> >> Signed-off-by: Tian Tao <tiantao6@xxxxxxxxxxxxx>
> >> ---
> >> drivers/tty/serial/owl-uart.c | 5 ++---
> >> 1 file changed, 2 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
> >> index c149f8c3..472fdaf 100644
> >> --- a/drivers/tty/serial/owl-uart.c
> >> +++ b/drivers/tty/serial/owl-uart.c
> >> @@ -251,10 +251,9 @@ static void owl_uart_receive_chars(struct uart_port *port)
> >> static irqreturn_t owl_uart_irq(int irq, void *dev_id)
> >> {
> >> struct uart_port *port = dev_id;
> >> - unsigned long flags;
> >> u32 stat;
> >>
> >> - spin_lock_irqsave(&port->lock, flags);
> >> + spin_lock(&port->lock);
> >
> > Same thing here; this will break with forced irq threading (i.e.
> > "threadirqs") since the console code can still end up being called from
> > interrupt context.
> As the following code shows, owl_uart_irq does not run in the irq
> threading context.
> ret = request_irq(port->irq, owl_uart_irq, IRQF_TRIGGER_HIGH,
> "owl-uart", port);
> if (ret)
> return ret;
It still runs in a thread when interrupts are forced to be threaded
using the kernel parameter "threadirqs".
We just had a revert of a change like yours after lockdep reported the
resulting lock inversion with forced interrupt threading.
Whether drivers should have to care about "threadirqs" is a somewhat
different question. Not sure how that's even supposed to work generally
unless we mass-convert drivers to spin_lock_irqsave() (or mark their
interrupts IRQF_NO_THREAD).
Thomas, any comments?
Johan
