nmi_watchdog suspicious

[Cyrill Gorcunov]

Ingo, Maciej, I've a really bad suspicious about commit

---
commit 3ed3f06295e69700fa808396f7b350bff2b69de0
Author: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Date:   Wed Jun 4 01:00:47 2008 +0400

    x86: nmi - consolidate nmi_watchdog_default for 32bit mode
    
    64bit mode bootstrap code does set nmi_watchdog to NMI_NONE
    by default and doing the same on 32bit mode is safe too.
    Such an action saves us from several #ifdef.
    
    Btw, my previous commit
    
    commit 19ec673ced067316b9732bc6d1c4ff4052e5f795
    Author: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
    Date:   Wed May 28 23:00:47 2008 +0400
    
        x86: nmi - fix incorrect NMI watchdog used by default
    
    did not fix the problem completely, moreover it
    introduced additional bug - nmi_watchdog would be
    set to either NMI_LOCAL_APIC or NMI_IO_APIC
    _regardless_ to boot option if being enabled thru
    /proc/sys/kernel/nmi_watchdog. Sorry for that.
    Fix it too.
---

actually it changed nmi behaviour much more then I thought.
Look, since by default nmi_watchdog now becomes NMI_NONE it
does mean nmi.c:touch_nmi_watchdog() will not reset apic timers
anymore even being requested by some other code.

This commit does affect 32bit mode _only_. So now I'm guessing
what mode was implemented in correct way originally.

On 64bit mode nmi_watchdog=NMI_NONE by default (in case if APIC enabled).
On 32bit mode nmi_watchdog=NMI_DEFAULT was by default (in any case,
but could be set to NMI_NONE in check_timer(), but we don't take
this case now).

So lets take a look on touch_nmi_watchdog().
There is the condition

	if (nmi_watchdog > 0)
		...tell to reset counters in nmi_watchdog_tick()

this condition is not taken on 64bit mode, but *was* taken on
32bit mode by default! So who was right then? 64bit version or 32bit?

Maciej, could you take a look please? Maybe I just missing figure
in general - ie how nmi_watchdog _should_ work.

		- Cyrill -
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/