[Linux-ia64] [RFC] Remove MCA dump?

[Linux-ia64] [RFC] Remove MCA dump?

[Matthew Wilcox]

The MCA handler is completely useless.  If I crash the machine and
forget to clear the MCA dump in firmware, at the next boot Linux dumps
the registers (in a hard-to-understand style) and hangs.  In its current
state, I'd rather it simply weren't in the kernel at all.

Do any platforms not have MCA handling facilities in firmware?

-- 
Revolutions do not require corporate support.

Re: [Linux-ia64] [RFC] Remove MCA dump?

[Andreas Schwab]

Matthew Wilcox <willy@debian.org> writes:

|> The MCA handler is completely useless.  If I crash the machine and
|> forget to clear the MCA dump in firmware, at the next boot Linux dumps
|> the registers (in a hard-to-understand style) and hangs.

I haven't seen such hangs on our machines, except for some old
pre-production systems that lack the necessary hardware support.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: [Linux-ia64] [RFC] Remove MCA dump?

[Matthew Wilcox]

On Wed, Aug 21, 2002 at 02:34:42PM +0200, Andreas Schwab wrote:
> Matthew Wilcox <willy@debian.org> writes:
> 
> |> The MCA handler is completely useless.  If I crash the machine and
> |> forget to clear the MCA dump in firmware, at the next boot Linux dumps
> |> the registers (in a hard-to-understand style) and hangs.
> 
> I haven't seen such hangs on our machines, except for some old
> pre-production systems that lack the necessary hardware support.

I wonder why not.  Here's the code:

void
init_handler_platform (struct pt_regs *regs)
{
        /* if a kernel debugger is available call it here else just dump the reg
isters */

        show_regs(regs);                /* dump the state info */
        while (1);                      /* hang city if no debugger */
}

Maybe it only locks up that specific processor so you didn't notice you'd
lost a processor on an SMP system?

-- 
Revolutions do not require corporate support.

Re: [Linux-ia64] [RFC] Remove MCA dump?

[Erich Focht]

On Wednesday 21 August 2002 13:51, Matthew Wilcox wrote:
> The MCA handler is completely useless.  If I crash the machine and
> forget to clear the MCA dump in firmware, at the next boot Linux dumps
> the registers (in a hard-to-understand style) and hangs.  In its current
> state, I'd rather it simply weren't in the kernel at all.

I'd also like to object to the statement above. The dumped registers are
fine and enough to get an idea where the system was and what it was doing.
My machines don't hang after the reboot. I'm using kdb and LKCD so
init_handler_platform looks completely different from yours, anyhow
I don't understand why that code should be executed _after_ you reboot.
Shouldn't the MCA logs come from ia64_log_print?

Regards,
Erich

RE: [Linux-ia64] [RFC] Remove MCA dump?

[Hall, Jenna S]

Yes they should.  There is no reason your system should hang *after* the
reboot if the MCA occurred before the reboot.  I also wonder if you've got
some old hardware or firmware...please let me know what HW/FW you're running
and I'll try to figure out why your system behaves this way upon reboot.

The MCA code is certainly not finished.  The logging is there, but the
recovery for MCAs is still in development by Intel and Bull engineers.  You
can disable the MCA logging in the .config but if your HW/FW is behaving
correctly it should not matter...besides, the logs do provide valuable
information in the case of a hardware failure (eg. flaky memory DIMM causing
sporadic hardware-corrected MCAs).

Further, the init_handler_platform() procedure is only called *during* an
INIT event - which is fatal and wouldn't be helped anyway if the MCA
recovery code was perfectly healthy.  The expected behavior of this
procedure is as you described - hang if no KDB enabled, jump into KDB if it
is enabled.  There is definitely something else going on with your system
beyond a simple MCA that occurred before the reboot.

Jenna

 -----Original Message-----
From: 	Erich Focht [mailto:efocht@ess.nec.de] 
Sent:	Wednesday, August 21, 2002 6:05 AM
To:	Matthew Wilcox; linux-ia64@linuxia64.org
Subject:	Re: [Linux-ia64] [RFC] Remove MCA dump?

On Wednesday 21 August 2002 13:51, Matthew Wilcox wrote:
> The MCA handler is completely useless.  If I crash the machine and
> forget to clear the MCA dump in firmware, at the next boot Linux dumps
> the registers (in a hard-to-understand style) and hangs.  In its current
> state, I'd rather it simply weren't in the kernel at all.

I'd also like to object to the statement above. The dumped registers are
fine and enough to get an idea where the system was and what it was doing.
My machines don't hang after the reboot. I'm using kdb and LKCD so
init_handler_platform looks completely different from yours, anyhow
I don't understand why that code should be executed _after_ you reboot.
Shouldn't the MCA logs come from ia64_log_print?

Regards,
Erich


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Re: [Linux-ia64] [RFC] Remove MCA dump?

[David Mosberger]

>>>>> On Wed, 21 Aug 2002 12:51:40 +0100, Matthew Wilcox <willy@debian.org> said:

  Matthew> The MCA handler is completely useless.

It's useful to me.

  Matthew> If I crash the machine and forget to clear the MCA dump in
  Matthew> firmware, at the next boot Linux dumps the registers (in a
  Matthew> hard-to-understand style) and hangs.

It shouldn't hang (and it doesn't on the Itanium & Itanium 2 systems
we have).  Sounds like something is off...

I agree that the output format is hard to understand, but a user-level
tool can fix that.  In my experience, the most useful value to look at
is CR[19], since it contains the IIP.  (It would be nice, though, to
have a beginners guide to decoding MCAs until there is better tools.)

	--david

Re: [Linux-ia64] [RFC] Remove MCA dump?

[David Mosberger]

>>>>> On Wed, 21 Aug 2002 13:38:32 +0100, Matthew Wilcox <willy@debian.org> said:

  Matthew> On Wed, Aug 21, 2002 at 02:34:42PM +0200, Andreas Schwab
  Matthew> wrote:
  >> Matthew Wilcox <willy@debian.org> writes:
  >> 
  >> |> The MCA handler is completely useless.  If I crash the machine
  >> and |> forget to clear the MCA dump in firmware, at the next boot
  >> Linux dumps |> the registers (in a hard-to-understand style) and
  >> hangs.
  >> 
  >> I haven't seen such hangs on our machines, except for some old
  >> pre-production systems that lack the necessary hardware support.

  Matthew> I wonder why not.  Here's the code:

  Matthew> void init_handler_platform (struct pt_regs *regs) { /* if a
  Matthew> kernel debugger is available call it here else just dump
  Matthew> the reg isters */

  Matthew>         show_regs(regs); /* dump the state info */ while
  Matthew> (1); /* hang city if no debugger */ }

  Matthew> Maybe it only locks up that specific processor so you
  Matthew> didn't notice you'd lost a processor on an SMP system?

This endless loop happens only in response to an INIT event.  The
boot-time MCA dump does not go through this path.

	--david