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Date:      Fri, 17 Aug 2018 10:02:08 +0100
From:      John Baldwin <jhb@FreeBSD.org>
To:        Michael Gmelin <freebsd@grem.de>
Cc:        Konstantin Belousov <kostikbel@gmail.com>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org>, Matthias Apitz <guru@unixarea.de>
Subject:   Re: Fatal trap 12: page fault on Acer Chromebook 720 (peppy)
Message-ID:  <8726bc32-6023-bfe1-7600-5b2c706236f8@FreeBSD.org>
In-Reply-To: <07E28AC5-EBE6-4893-810A-6C03F07925C8@grem.de>
References:  <20180603215020.452a81d8@bsd64.grem.de> <20180603205340.GS3789@kib.kiev.ua> <20180604004632.56ca6afa@bsd64.grem.de> <20180604110654.GA2450@kib.kiev.ua> <20180604231756.2ed2adb9@bsd64.grem.de> <20180605131135.GH2450@kib.kiev.ua> <20180606010625.62632920@bsd64.grem.de> <20180815005106.69402d23@bsd64.grem.de> <20180815130447.GZ2340@kib.kiev.ua> <C26CD25D-3CB0-4F7E-8B50-F7E95E16B776@grem.de> <20180815135531.GA2340@kib.kiev.ua> <FAEA5B0A-5302-4A48-B322-21CB0D97C8CC@grem.de> <e82ed552-83b0-5331-3117-6750b8c205f7@FreeBSD.org> <07E28AC5-EBE6-4893-810A-6C03F07925C8@grem.de>

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On 8/17/18 9:54 AM, Michael Gmelin wrote:
> 
> 
>> On 17. Aug 2018, at 08:17, John Baldwin <jhb@FreeBSD.org> wrote:
>>
>>> On 8/16/18 1:58 PM, Michael Gmelin wrote:
>>>
>>>
>>>> On 15. Aug 2018, at 15:55, Konstantin Belousov <kostikbel@gmail.com <mailto:kostikbel@gmail.com>> wrote:
>>>>
>>>>> On Wed, Aug 15, 2018 at 03:52:37PM +0200, Michael Gmelin wrote:
>>>>>
>>>>>
>>>>>>> On 15. Aug 2018, at 15:04, Konstantin Belousov <kostikbel@gmail.com <mailto:kostikbel@gmail.com>> wrote:
>>>>>>>
>>>>>>> On Wed, Aug 15, 2018 at 12:51:06AM +0200, Michael Gmelin wrote:
>>>>>>> Reviving this old thread, since I just updated to r337818 and a similar
>>>>>>> problem is happening again. Since the fix in r334799 (review
>>>>>>> https://reviews.freebsd.org/D15675) (mp_)machdep.c have been touched,
>>>>>>> so maybe this is related
>>>>>>> (https://svnweb.freebsd.org/base?view=revision&revision=334799).
>>>>>>>
>>>>>>> Please see the screenshot of the panic below:
>>>>>>> https://gist.github.com/grembo/78d0f2a100dd4f16775b85a118769658
>>>>>>>
>>>>>>> This is me not digging any deeper, hoping that this is something
>>>>>>> obvious. Please let me know if you need more input.
>>>>>>
>>>>>> I do not see how recent mp_machdep.c changes could affect this.
>>>>>> Can you try newest kernel but old loader ?
>>>>>
>>>>> I will try (but that will take a while). Oh, also, it still boots in save mode/with smp disabled.
>>>>
>>>> Right, this is because the access to that address through DMAP is only
>>>> needed when configuring AP startup resources.
>>>>
>>>> Also, I think it is safe to suggest that the bisect is needed.
>>>
>>> Using an older loader didn’t help, but I identified the problem:
>>>
>>> https://svnweb.freebsd.org/base?view=revision&revision=334952
>>>
>>> modified the code you introduced in
>>>
>>> https://svnweb.freebsd.org/base?view=revision&revision=334799
>>>
>>> By correcting units to pages it also broke booting the Chromebook as a side effect - so the previous fix just worked due to a bug it seems.
>>>
>>> Is there an easy way to output the content of physmap at that point (debug.late_console=0 doesn’t work) - like an existing buffer I could use, or would this be more elaborate (I did something complicated last time but didn’t save it, so any simple solution would be preferred).
>>
>> How about reverting the commit for now so you get a working console
>> and print out the physmap array values along with Maxmem later in
>> the boot (or just use kgdb to examine them once the system is running)?
>>
> 
> This is before the system has a working console (part of calling getmem...), disabling late console makes it hang, physmap changes afterwards, so running kgdb later doesn’t help. Last time I kept a copy of physmap and logged it later to know the original content. I can do that again, I just thought maybe there is a simple mechanism I’m not aware of that would save me some time.

I thought we only modified phys_avail[], but saving a copy of physmap[] and
dumping it from kgdb is probably the simplest thing to do.

-- 
John Baldwin



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