linux-kernel - Re: [PATCH] mm/page_isolation: don't putback unisolated page

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Date:   Thu, 9 Sep 2021 11:07:25 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Hildenbrand <david@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page

On 9/9/21 10:56, David Hildenbrand wrote:
> On 09.09.21 00:42, John Hubbard wrote:
>> On 9/7/21 2:56 AM, David Hildenbrand wrote:
>> ...
>>>> If this can be handled gracefully, then I'd rather go with VM_WARN_ON.
>>>> Maybe even WARN_ON_ONCE?
>>>>
>>>
>>> I think either VM_BUG_ON() or VM_WARN_ON() -- compiling the runtime
>>> checks out -- should be good
>>> enough.
>>>
>>> I'd just go with VM_BUG_ON(), because anybody messing with
>>> __isolate_free_page() should clearly spot
>>> that we expect the current handling. But no strong opinion.
>>>
>>
>> If in doubt, WARN*() should be preferred over BUG*(). There's a pretty long
>> history of "don't kill the machine unless you have to" emails about this, let
>> me dig up one...OK, maybe not the best example, but the tip of the iceberg:
> 
> Please note the subtle difference between BUG_ON and VM_BUG_ON. We expect
> VM_BUG_ON to be compiled out on any production system. So it's really only a
> mean to identify things that really shouldn't be like that during
> debugging/testing.

IIRC Fedora used to have CONFIG_DEBUG_VM enabled, did it change?

> Using WARN... instead of VM_BUG_ON is even worse for production systems.
> There are distros that set panic_on_warn, essentially converting WARN...
> into BUG...

Uh, does any distro really do that?