Message-ID: <77d17dbf-1609-41b1-9244-488d2ce75b33@redhat.com>
Date: Mon, 4 Aug 2025 14:49:53 +0200
From: David Hildenbrand <david@...hat.com>
To: Eugen Hristev <eugen.hristev@...aro.org>, Michal Hocko <mhocko@...e.com>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-mm@...ck.org, tglx@...utronix.de,
 andersson@...nel.org, pmladek@...e.com,
 linux-arm-kernel@...ts.infradead.org, linux-hardening@...r.kernel.org,
 corbet@....net, mojha@....qualcomm.com, rostedt@...dmis.org,
 jonechou@...gle.com, tudor.ambarus@...aro.org
Subject: Re: [RFC][PATCH v2 22/29] mm/numa: Register information into Kmemdump

On 04.08.25 14:29, Eugen Hristev wrote:
> 
> 
> On 8/4/25 15:18, David Hildenbrand wrote:
>> On 04.08.25 13:06, Eugen Hristev wrote:
>>>
>>>
>>> On 8/4/25 13:54, Michal Hocko wrote:
>>>> On Wed 30-07-25 16:04:28, David Hildenbrand wrote:
>>>>> On 30.07.25 15:57, Eugen Hristev wrote:
>>>> [...]
>>>>>> Yes, registering after is also an option. Initially this is how I
>>>>>> designed the kmemdump API, I also had in mind to add a flag, but, after
>>>>>> discussing with Thomas Gleixner, he came up with the macro wrapper idea
>>>>>> here:
>>>>>> https://lore.kernel.org/lkml/87ikkzpcup.ffs@tglx/
>>>>>> Do you think we can continue that discussion , or maybe start it here ?
>>>>>
>>>>> Yeah, I don't like that, but I can see how we ended up here.
>>>>>
>>>>> I also don't quite like the idea that we must encode here what to include in
>>>>> a dump and what not ...
>>>>>
>>>>> For the vmcore we construct it at runtime in crash_save_vmcoreinfo_init(),
>>>>> where we e.g., have
>>>>>
>>>>> VMCOREINFO_STRUCT_SIZE(pglist_data);
>>>>>
>>>>> Could we similar have some place where we construct what to dump similarly,
>>>>> just not using the current values, but the memory ranges?
>>>>
>>>> All those symbols are part of kallsyms, right? Can we just use kallsyms
>>>> infrastructure and a list of symbols to get what we need from there?
>>>>
>>>> In other words the list of symbols to be completely external to the code
>>>> that is defining them?
>>>
>>> Some static symbols are indeed part of kallsyms. But some symbols are
>>> not exported, for example patch 20/29, where printk related symbols are
>>> not to be exported. Another example is with static variables, like in
>>> patch 17/29 , not exported as symbols, but required for the dump.
>>> Dynamic memory regions are not have to also be considered, have a look
>>> for example at patch 23/29 , where dynamically allocated memory needs to
>>> be registered.
>>>
>>> Do you think that I should move all kallsyms related symbols annotation
>>> into a separate place and keep it for the static/dynamic regions in place ?
>>
>> If you want to use a symbol from kmemdump, then make that symbol
>> available to kmemdump.
> 
> That's what I am doing, registering symbols with kmemdump.
> Maybe I do not understand what you mean, do you have any suggestion for
> the static variables case (symbols not exported) ?

Let's use patch #20 as example:

What I am thinking is that you would not include "linux/kmemdump.h" and 
not leak all of that KMEMDUMP_ stuff in all these files/subsystems that 
couldn't less about kmemdump.

Instead of doing

static struct printk_ringbuffer printk_rb_dynamic;

You'd do

struct printk_ringbuffer printk_rb_dynamic;

and have it in some header file, from where kmemdump could lookup the 
address.

So you move the logic of what goes into a dump from the subsystems to
the kmemdump core.

-- 
Cheers,

David / dhildenb

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