Re: tickle nmi watchdog whilst doing serial writes.

Ed Tomlinson
2005-05-14T10:54:52Z

Hi,

The message from a+s+T on a serial console (x86_64) is:
BUG: soft lockup detected on cpu#0
Its not changed by this patch. Probably would be a good idea to correct this?

Ed

On Saturday 14 May 2005 06:31, Ed Tomlinson wrote:
> Suspect this can be triggered using alt+sysreq+T on a busy system with a slow
> serial console. Might be a easy way to see if this patch fixes the issue?
>
> Ed Tomlinson
>
> On Saturday 14 May 2005 03:07, Andrew Morton wrote:
> > 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();
> > + }
> > }
> > }
> >
> > _
> >
> > -
>