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    SubjectRe: [PATCH -v2 7/7] x86, NMI, Remove do_nmi_callback logic
    On Tue, Sep 28, 2010 at 08:28:25AM +0800, Huang Ying wrote:
    > Hi, Don,
    >
    > On Mon, 2010-09-27 at 23:16 +0800, Don Zickus wrote:
    > > On Mon, Sep 27, 2010 at 03:43:41PM +0200, Robert Richter wrote:
    > > > On 27.09.10 08:56:44, huang ying wrote:
    > > >
    > > > > >> -static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu)
    > > > > >> -{
    > > > > >> - unsigned char reason = get_nmi_reason();
    > > > > >> - char buf[64];
    > > > > >> -
    > > > > >> - sprintf(buf, "NMI received for unknown reason %02x\n", reason);
    > > > > >> - die_nmi(buf, regs, 1); /* Always panic here */
    > > > > >> - return 0;
    > > > > >
    > > > > > You are dropping this code that is different to panic().
    > > > >
    > > > > What is the difference? Is it relevant?
    > > >
    > > > I think yes, since the code behaves different. Otherwise we could
    > > > remove die_nmi() completly and replace it by panic(). But both are
    > > > different implementions. Maybe we can merge the code, but I didn't
    > > > look at it closly.
    > >
    > > Actually die_nmi is a wrapper around panic with two important pieces.
    > > One, it dumps some registers and two it does another notifier call to
    > > DIE_NMIWATCHDOG (which correlates to another discussion in this patch
    > > series).
    > >
    > > So if we do any consolidation between panic and die_nmi, it should be
    > > convert to die_nmi. But then I wonder if that breaks the original
    > > semantics of 'panic_on_unrecovered_nmi'. I don't think so though.
    >
    > Please take a look at the original code:
    >
    >
    > if (nmi_watchdog_tick(regs, reason))
    > return;
    > if (!do_nmi_callback(regs, cpu))
    > #endif /* !CONFIG_LOCKUP_DETECTOR */
    > unknown_nmi_error(reason, regs);
    > #else
    > unknown_nmi_error(reason, regs);
    > #endif
    >
    > If NMI comes from watchdog, nmi_watchdog_tick() will return 1. So
    > do_nmi_callback() is NOT for watchdog NMI, but for unknown NMI. Why do
    > we call DIE_NMIWATCHDOG for unknown NMI (NOT watchdog NMI)? die_nmi is
    > for watchdog, not unknown NMI.

    I think watchdog is an overloaded term. I was under the impression that
    once the nmi watchdog determined a problem, it called the DIE_NMIWATCHDOG
    die chain to see if any other drivers wanted to clean up or do their thing
    first before panic'ing (namely drivers in drivers/char/watchdog).

    Cheers,
    Don


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