Re: tickle nmi watchdog whilst doing serial writes.

Andrew Morton
2005-05-14T07:08:39Z

Dave Jones <davej@redhat.com> wrote:
>
> On Fri, May 13, 2005 at 11:43:31PM -0700, Andrew Morton wrote:
> > Dave Jones <davej@redhat.com> wrote:
> > >
> > > This was fun. I inserted a music CD with some obnoxious copy-protection
> > > on it into the drive, and lots of SCSI errors went zipping over to
> > > the serial console. Unfortunatly, the box was also compiling a kernel,
> > > playing oggs, and doing a number of other things at the same time,
> > > so this happened..
> > >
> > > NMI Watchdog detected LOCKUP on CPU2CPU 2
> >
> > OK.. But calling touch_nmi_watchdog() at 1MHz seems a bit excessive, and
> > might perturb the finely-tuned timing in there.
> >
> > How's about this?
>
> Umm.. Despite it being past my bedtime, I'm pretty sure I'm
> missing something here...
>
> > + while (!(serial_in(up, UART_MSR) & UART_MSR_CTS) && --tmout)
> > udelay(1);
>
> I don't see how this is any better than the current code.
> We're doing 1000000 udelays. Whilst we're doing that,
> the nmi watchdog goes bonkers.
>
> > + if (tmout < 1000000)
> > + touch_nmi_watchdog();
>
> So by the time we do this, its already triggered.

But the NMI watchdog won't expire after one second - normally it's set to
fixe seconds.

> How about..
>
> --- linux-2.6.11/drivers/serial/8250.c~ 2005-05-14 02:49:02.000000000 -0400
> +++ linux-2.6.11/drivers/serial/8250.c 2005-05-14 02:54:30.000000000 -0400
> @@ -40,6 +40,7 @@
> #include <linux/serial_core.h>
> #include <linux/serial.h>
> #include <linux/serial_8250.h>
> +#include <linux/nmi.h>
>
> #include <asm/io.h>
> #include <asm/irq.h>
> @@ -2099,8 +2100,15 @@ static inline void wait_for_xmitr(struct
> if (up->port.flags & UPF_CONS_FLOW) {
> tmout = 1000000;
> while (--tmout &&
> - ((serial_in(up, UART_MSR) & UART_MSR_CTS) == 0))
> + ((serial_in(up, UART_MSR) & UART_MSR_CTS) == 0)) {
> + int cnt=0;
> udelay(1);
> + cnt++;
> + if (cnt==100) {
> + touch_nmi_watchdog();
> + cnt=0;
> + }
> + }

<obwhitespacewhine> spose so.

--- 25/drivers/serial/8250.c~tickle-nmi-watchdog-whilst-doing-serial-writes 2005-05-14 00:03:09.000000000 -0700
+++ 25-akpm/drivers/serial/8250.c 2005-05-14 00:06:53.000000000 -0700
@@ -40,6 +40,7 @@
#include <linux/serial_core.h>
#include <linux/serial.h>
#include <linux/serial_8250.h>
+#include <linux/nmi.h>

#include <asm/io.h>
#include <asm/irq.h>
@@ -2098,9 +2099,11 @@ static inline void wait_for_xmitr(struct
/* Wait up to 1s for flow control if necessary */
if (up->port.flags & UPF_CONS_FLOW) {
tmout = 1000000;
- while (--tmout &&
- ((serial_in(up, UART_MSR) & UART_MSR_CTS) == 0))
+ while (!(serial_in(up, UART_MSR) & UART_MSR_CTS) && --tmout) {
udelay(1);
+ if ((tmout % 1000) == 0)
+ touch_nmi_watchdog();
+ }
}
}

_