linux-kernel - Re: [PATCH v3 11/12] mm/gup_benchmark: support pin_user

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Date:   Mon, 3 Feb 2020 14:07:33 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        <linux-doc@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 11/12] mm/gup_benchmark: support pin_user_pages() and
 related calls

On 2/3/20 1:55 PM, Kirill A. Shutemov wrote:
> On Mon, Feb 03, 2020 at 01:17:40PM -0800, John Hubbard wrote:
>> On 2/3/20 5:58 AM, Kirill A. Shutemov wrote:
>> ...
>>>> @@ -19,6 +21,48 @@ struct gup_benchmark {
>>>>  	__u64 expansion[10];	/* For future use */
>>>>  };
>>>>  
>>>> +static void put_back_pages(unsigned int cmd, struct page **pages,
>>>> +			   unsigned long nr_pages)
>>>> +{
>>>> +	int i;
>>>> +
>>>> +	switch (cmd) {
>>>> +	case GUP_FAST_BENCHMARK:
>>>> +	case GUP_LONGTERM_BENCHMARK:
>>>> +	case GUP_BENCHMARK:
>>>> +		for (i = 0; i < nr_pages; i++)
>>>
>>> 'i' is 'int' and 'nr_pages' is 'unsigned long'.
>>> There's space for trouble :P
>>>
>>
>> Yes, I've changed it to "unsigned int", thanks.
> 
> I'm confused. If nr_pages is more than UINT_MAX, this is endless loop.
> Hm?
> 

Oh, I've been afflicted with 64-bit tunnel vision. OK, make that 
"unsigned long" and "%ul". yikes. :)



thanks,
-- 
John Hubbard
NVIDIA