linux-kernel - Re: [mm/slub] ae107fa919: BUG:unable_to_handle_page_fault_for

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Message-ID: <ff4daab3-0ae6-65b9-dbc6-8033cf7ad6a7@suse.cz>
Date:   Sat, 12 Mar 2022 14:08:16 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mike Rapoport <rppt@...nel.org>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     kernel test robot <oliver.sang@...el.com>,
        Oliver Glitta <glittao@...il.com>, lkp@...ts.01.org,
        lkp@...el.com, LKML <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org
Subject: Re: [mm/slub] ae107fa919: BUG:unable_to_handle_page_fault_for_address

On 3/12/22 13:06, Mike Rapoport wrote:
>>>> Ideas? implementing something like kmem_cache_init_early() again?
>>>
>>> I think we could simply make CONFIG_SLUB_DEBUG_ON select/depend on
>>> STACKDEPOT_ALWAYS_INIT?
>>
>> Oh, sounds better.
>>
>> If we make CONFIG_SLUB_DEBUG_ON select STACK_DEPOT_ALWAYS_INIT,
>> that is simple solution. but stackdepot will be initialized on
>> slub_debug=- too.

Valid point.

>> But I think no one will set CONFIG_SLUB_DEBUG_ON=y if not debugging...
> 
> If memory wasted by stack_table is a real concern, we may free it after
> parsing slub_debug or add a condition taking into account
> CONFIG_SLUB_DEBUG_ON and slub_debug=- to the 
> 
> 	if (slub_debug & SLAB_STORE_USER)
> 		stack_depot_want_early_init();
> 
> But I agree that if somebody runs a kernel with CONFIG_SLUB_DEBUG_ON=y, the
> goal is to have slub debugging on, so making CONFIG_SLUB_DEBUG_ON select
> STACK_DEPOT_ALWAYS_INIT totally makes sense to me.

Agree. We had to decouple stackdpepot init from CONFIG_SLUB_DEBUG
because almost everyone enables CONFIG_SLUB_DEBUG by default, but on
smaller systems doesn't want to always pay the price even if unused.
But I don't expect anyone to enable CONFIG_SLUB_DEBUG_ON and then run
with slub_debug=- by default, and complain. If anyone like that exists,
they could also add the stackdepot_disable parameter.

>> I don't think making CONFIG_SLUB_DEBUG_ON depend on
>> CONFIG_STACKDEPOT_ALWAYS_INIT is good solution. only KASAN selects it.
>>
>> -- 
>> Thank you, You are awesome!
>> Hyeonggon :-)
>