linux-kernel - Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb

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Date:	Tue, 7 May 2013 20:51:08 -0400
From:	Jerome Glisse <j.glisse@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jerome Glisse <jglisse@...hat.com>
Subject: Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

On Tue, May 7, 2013 at 8:47 PM, KOSAKI Motohiro
<kosaki.motohiro@...il.com> wrote:
> On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@...il.com> wrote:
>> From: Jerome Glisse <jglisse@...hat.com>
>>
>> Do not increase page count if FOLL_GET is not set. None of the
>> current user can trigger the issue because none of the current
>> user call __get_user_pages with both the pages array ptr non
>> NULL and the FOLL_GET flags non set in other word all caller
>> of __get_user_pages that don't set the FOLL_GET flags also call
>> with pages == NULL.
>
> Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.

Yes but this allow pages != NULL and FOLL_GET not set and as i said
there is no such user of that yet and this is exactly what i was
trying to use.

Cheers,
Jerome

>
> long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> {
> (snip)
>     VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
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