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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH 03/10] mm: Convert p[te|md]_numa users to
 p[te|md]_protnone_numa
In-Reply-To: <1417473849.7182.9.camel@kernel.crashing.org>
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 <1416578268-19597-4-git-send-email-mgorman@suse.de>
 <1417473849.7182.9.camel@kernel.crashing.org>
Date: Tue, 02 Dec 2014 13:01:29 +0530
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Cc: Rik van Riel <riel@redhat.com>,
 Linus Torvalds <torvalds@linux-foundation.org>,
 Hugh Dickins <hughd@google.com>, Linux Kernel <linux-kernel@vger.kernel.org>,
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Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:

> On Fri, 2014-11-21 at 13:57 +0000, Mel Gorman wrote:
>> void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
>>                 pte_t pte)
>>  {
>> -#ifdef CONFIG_DEBUG_VM
>> -       WARN_ON(pte_val(*ptep) & _PAGE_PRESENT);
>> -#endif
>> +       /*
>> +        * When handling numa faults, we already have the pte marked
>> +        * _PAGE_PRESENT, but we can be sure that it is not in hpte.
>> +        * Hence we can use set_pte_at for them.
>> +        */
>> +       VM_WARN_ON((pte_val(*ptep) & (_PAGE_PRESENT | _PAGE_USER)) ==
>> +               (_PAGE_PRESENT | _PAGE_USER));
>> +
>
> His is that going to fare with set_pte_at() called for kernel pages ?
>

Yes, we won't capture those errors now. But is there any other debug
check i could use to capture the wrong usage of set_pte_at ?

-aneesh