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Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page
To:     John Hubbard <jhubbard@nvidia.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Miaohe Lin <linmiaohe@huawei.com>, akpm@linux-foundation.org
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        linux-kernel@vger.kernel.org
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <efdab0d6-199a-1bb8-79bf-ea0a5b94c093@redhat.com>
Date:   Thu, 9 Sep 2021 10:56:55 +0200
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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.

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...

-- 
Thanks,

David / dhildenb