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From:   John Hubbard <jhubbard@nvidia.com>
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On 2020-04-14 14:35, Kirill A. Shutemov wrote:
> On Mon, Apr 13, 2020 at 01:48:22PM -0700, John Hubbard wrote:
> 
> [Thanks for all your suggestions and corrections]
> 
>>> +	if (IS_ENABLED(CONFIG_DEBUG_VM) && expected_refcount > refcount) {
>>> +		pr_err("expected_refcount: %d, refcount: %d\n",
>>> +				expected_refcount, refcount);
>>> +		dump_page(page, "Unexpected refcount");
>>
>>
>> I see two issues with the pr_err() and the dump_page() call:
>>
>> 1. You probably want to rate limit this, otherwise you'll have a big
>> problem if lots of pages are pinned!
> 
> Nope. Only if kernel is buggy. See below.
> 
>> 2. Actually, I don't think you'd want to print anything at all here, even with
>> rate limiting, because doing so presumes that "unexpected" means "wrong". And I
>> think this patch doesn't expect to have GUP pins (or pin_user_pages() pins, ha),
>> but that doesn't mean that they're wrong to have.
> 
> See condition. We only do it if refcount is *below* expected refcount. It
> should never happen. Pinned page would have refcount above expected.
> 

Yes, you are right. I misread the condition. This actually is just right. :)

thanks,
-- 
John Hubbard
NVIDIA