Re: enabling kernel dump options in GENERIC

On 2018-May-18, at 8:11 AM, Mark Johnston <markj at reeBSD.org> wrote:

> On Fri, May 18, 2018 at 06:14:50AM -0700, Mark Millard wrote:
>> On 2018-May-17, at 11:17 PM, Mark Johnston <markj at FreeBSD.org> wrote:
>> 
>>> On Thu, May 17, 2018 at 08:58:16PM -0700, Mark Millard wrote:
>>>> . . .
>>>> Bugzilla 214598 (from late 2016) was about
>>>> dump for TARGET_ARCH=powerpc64 builds getting
>>>> failures like:
>>>> 
>>>> KDB: enter: manual escape to debugger
>>>> [ thread pid 12 tid 10018 ]
>>>> Stopped at       .kdb_enter+0x70:       ori r0, r0, 0x0
>>>> db> dump
>>>> Dumping 9 MB (3 chunks)
>>>> chunk 0: 10MB (2510 pages) ... ok
>>>> chunk 1: 1MB (24 pages) ... ok
>>>> chunk 2: 1MB (2 pages)panic: vm_fault: fault on nofault entry, addr: c000000000022000
>>>> 
>>>> (A 32-bit powerpc build on the same machine worked
>>>> fine for dumping.)
>>>> 
>>>> I just tried it with head -r333594 and I got something
>>>> similar. (Old and new mention routines with _bus_dma_map_
>>>> in the names near the trap in the call stack. I've not
>>>> done a detailed comparison.)
>>> 
>>> What is the call stack?
>> 
>> I'll have to induce the failure, take a picture of
>> the screen that results, and hand type in the
>> material for the fairly modern backtrace (-r333594).
>> I will not be able to do this until later today.
>> 
>> The bugzilla report has the old backtrace. I did not
>> quote all the material from that report in the above.
>> So there is something to compare against once I
>> supply a modern one.
> 
> My apologies, I missed the fact that the backtrace was included in that
> PR. Since the problem still occurs and apparently manifests with a
> similar backtrace, it wouldn't be useful to retest. I'm afraid I don't
> have any suggestions on how to make progress here. Given that the new
> options give only a small increase in the kernel size, I'm still
> inclined to enable them on powerpc64 for consistency with other
> architectures.

Seems reasonable. May be there are other powerpc64 contexts
that can test the updates.

Useful or not, I've updated bugzilla 214598 with a backtrace
from head -r333594 and have updated its one-line summary to
reference -r333594 .

Looks like I missed a 0 in:

0xe7ced0: at 0xc00000006ab17fc

it should be:

0xe7ced0: at 0xc000000006ab17fc

I've no clue why this address has no symbol.

I showed more of the stack this time.

At least now the old and new can be compared. That
is better than forcing folks to rely on my earlier
quick look.

>> Also: in about a week I'll lose access to the PowerMacs
>> for an unknown period of time (weeks? months?).
>> 

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)

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