Re: [PATCH 1/3] watchdog: hpwdt: add ioctl WDIOC_GETPRETIMEOUT

From: Jerry Hoemann
Date: Sat Oct 21 2017 - 21:41:09 EST


On Fri, Oct 20, 2017 at 07:25:20PM -0700, Guenter Roeck wrote:
> On 10/20/2017 03:54 PM, Jerry Hoemann wrote:
> > Add support for WDIOC_GETPRETIMEOUT ioctl so that user applications
> > can determine when the NMI should arrive.
> >
> > Signed-off-by: Jerry Hoemann <jerry.hoemann@xxxxxxx>
> > ---
> > drivers/watchdog/hpwdt.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c
> > index 67fbe35..ef54b03 100644
> > --- a/drivers/watchdog/hpwdt.c
> > +++ b/drivers/watchdog/hpwdt.c
> > @@ -50,6 +50,7 @@
> > static bool nowayout = WATCHDOG_NOWAYOUT;
> > static char expect_release;
> > static unsigned long hpwdt_is_open;
> > +static const int pretimeout = 9;
> > static void __iomem *pci_mem_addr; /* the PCI-memory address */
> > static unsigned long __iomem *hpwdt_timer_reg;
> > @@ -622,6 +623,12 @@ static long hpwdt_ioctl(struct file *file, unsigned int cmd,
> > }
> > break;
> > + case WDIOC_GETPRETIMEOUT:
> > + ret = copy_to_user(argp, &pretimeout, sizeof(pretimeout));
> > + if (ret)
> > + ret = -EFAULT;
> > + break;
> > +
> > case WDIOC_SETTIMEOUT:
> > ret = get_user(new_margin, p);
> > if (ret)
> >
>
> Can you please convert the driver to use the watchdog subsystem instead ?
> If there are still improvements needed afterwards, they can still be
> implemented, but we really should not make improvements which are
> already supported by the watchdog core.

I will look into converting the driver, but would like to get this
fix in independently.

SuSE brought https://bugzilla.novell.com/show_bug.cgi?id=1042933
to my attention earlier this summer. The submitter was trying to
develop a watchdog test where the ping rate was set to be the
Timeout/2.

The test worked fine until (Timeout/2) < PreTimeout. At this point
an NMI would be delivered to the system before the test could refresh
the timer.

I came to the view that a watchdog that implements a pre-timeout NMI
where the value of the pre-timeout is not known programmatically as having
a defect.

This problem has been around a long time and we could live with it, but
figured while I was in fixing other problems, I'd fix this one as well.

Thanks

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Jerry Hoemann Software Engineer Hewlett Packard Enterprise
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