Re: [Xen-devel] [PATCH] Xen: Force non-irq keyhandler to be run in tasklet when receive a debugkey from serial port

["Lan, Tianyu" <tianyu.lan@xxxxxxxxx>]

On 10/24/2016 6:53 PM, Jan Beulich wrote:
> > > > On 22.10.16 at 13:23, <tianyu.lan@xxxxxxxxx> wrote:
> > __serial_rx() runs in either irq handler or timer handler and non-irq
> > keyhandler should not run in these contexts. So always force non-irq
> > keyhandler to run in tasklet when receive a debugkey from serial port
> >
> > Signed-off-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
> > ---
> >  xen/drivers/char/console.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> > index b0f74ce..184b523 100644
> > --- a/xen/drivers/char/console.c
> > +++ b/xen/drivers/char/console.c
> > @@ -347,7 +347,7 @@ static void switch_serial_input(void)
> >  static void __serial_rx(char c, struct cpu_user_regs *regs)
> >  {
> >      if ( xen_rx )
> > -        return handle_keypress(c, regs, !in_irq());
> > +        return handle_keypress(c, regs, true);
> Together with one of your earlier patches having got reverted, I
> think we need to take a step back here instead of going back to
> what was requested to be changed from v2 of the original patch.
> In particular I assume that the problem you're trying to address is
> not limited to dump_timerq() - at least dump_runq() should be as
> problematic on many-CPU systems.
I think the issue here is that my previous patch commit
610b4eda2c("keyhandler: rework process of nonirq keyhandler") makes
non-irq keyhandler run in irq context. This is caused by input param
"!in_irq()" which is false in irq context. handle_keypress() runs 
keyhandler synchronically. This patch fixes the issue.
> I think (and I vaguely recall possibly having said so during earlier
> review) that dump functions the output of which depends on CPU
> count should get modeled after dump_registers(), and it might be
> worth abstracting this in keyhandler.c.
Yes, but this sounds like a new feature or framework rework rather than 
a fix patch.

> In any case quite likely the
> other patch of yours (which the one here basically modifies) may
> then also want to be reverted.
I think patch "timer: process softirq during dumping timer"
does right thing. The issue is triggered by previous patch.


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