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SubjectRe: [RFC PATCH 4/4] watchdog: hpwdt: Make panic behaviour configurable
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On Tue, 2019-01-15 at 19:30 -0700, Jerry Hoemann wrote:
> On Mon, Jan 14, 2019 at 07:36:17AM +0500, Ivan Mironov wrote:
> > This adds an option to not panic on NMI even if it was caused by iLO.
> >
> > Signed-off-by: Ivan Mironov <mironov.ivan@gmail.com>
> > ---
> > drivers/watchdog/hpwdt.c | 19 ++++++++++++++++---
> > 1 file changed, 16 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c
> > index 95d002b5b120..b12858491189 100644
> > --- a/drivers/watchdog/hpwdt.c
> > +++ b/drivers/watchdog/hpwdt.c
> > @@ -37,6 +37,10 @@ static unsigned int soft_margin = DEFAULT_MARGIN; /* in seconds */
> > static bool nowayout = WATCHDOG_NOWAYOUT;
> > static bool pretimeout = IS_ENABLED(CONFIG_HPWDT_NMI_DECODING);
> >
> > +#ifdef CONFIG_HPWDT_NMI_DECODING
> > +static bool panic_on_nmi = true;
> > +#endif /* CONFIG_HPWDT_NMI_DECODING */
> > +
> > static void __iomem *pci_mem_addr; /* the PCI-memory address */
> > static unsigned long __iomem *hpwdt_nmistat;
> > static unsigned long __iomem *hpwdt_timer_reg;
> > @@ -146,7 +150,10 @@ static int hpwdt_set_pretimeout(struct watchdog_device *wdd, unsigned int req)
> >
> > static int hpwdt_my_nmi(void)
> > {
> > - return ioread8(hpwdt_nmistat) & 0x6;
> > + int nmistat = ioread8(hpwdt_nmistat);
> > +
> > + iowrite8(nmistat & ~0x6, hpwdt_nmistat);
> > + return nmistat & 0x6;
>
> This is a read only register.
>

Oops... At least on my system this code has the desired effect:
subsequent function call returns zero.

Probably it would be better to use additional variable to determine
whether NMI from iLO already happened or not.

>
> > }
> >
> > /*
> > @@ -168,7 +175,10 @@ static int hpwdt_pretimeout(unsigned int ulReason, struct pt_regs *regs)
> > "4. iLO Event Log\n",
> > mynmi, ulReason, smp_processor_id());
> >
> > - nmi_panic(regs, "hpwdt: NMI: Not continuing");
> > + if (panic_on_nmi)
> > + nmi_panic(regs, "hpwdt: NMI: Not continuing");
> > +
> > + pr_emerg("Dazed and confused, but trying to continue\n");
> >
>
> The watchdog core provides a way to enable/disable the NMI pretimeout dynamically
> via ioctl. The pretimeout NMI can also be disabled via module parameter to hpwdt.
> This adds complexity without really adding functionality.
>

It looks like disabling pretimout will disable panics only for iLO 5
(mine system has iLO 2). Or am I missing something?

>
> BTW, don't reuse error messages. Makes it difficult to tell where the error
> originated from.
>

Would it be better to just return NMI_DONE and thus reuse normal NMI
handling from kernel, with logging and panic/don't panic logic?

>
> > return NMI_HANDLED;
> > }
> > @@ -376,6 +386,9 @@ MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default="
> > #ifdef CONFIG_HPWDT_NMI_DECODING
> > module_param(pretimeout, bool, 0);
> > MODULE_PARM_DESC(pretimeout, "Watchdog pretimeout enabled");
> > -#endif
> > +
> > +module_param(panic_on_nmi, bool, 0);
> > +MODULE_PARM_DESC(panic_on_nmi, "Cause panic on NMI induced by iLO (default=1)");
> > +#endif /* CONFIG_HPWDT_NMI_DECODING */
> >
> > module_pci_driver(hpwdt_driver);
> > --
> > 2.20.1

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