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Date: Mon, 31 Jan 2011 17:08:59 -0800
Message-ID: <AANLkTimycdE11kyPSxpVHuCLV7wshj-CPt+HVNcJsTTZ@mail.gmail.com>
Subject: Re: [PATCH] mlock: operate on any regions with protection != PROT_NONE
From: Michel Lespinasse <walken@google.com>
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Sender: owner-linux-mm@kvack.org
To: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tao Ma <tm@tao.ma>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>
List-ID: <linux-mm.kvack.org>

(forgot the signoff...)

On Mon, Jan 31, 2011 at 5:03 PM, Michel Lespinasse <walken@google.com> wrot=
e:
> As Tao Ma noticed, change 5ecfda0 breaks blktrace. This is because
> blktrace mmaps a file with PROT_WRITE permissions but without PROT_READ,
> so my attempt to not unnecessarity break COW during mlock ended up
> causing mlock to fail with a permission problem.
>
> I am proposing to let mlock ignore vma protection in all cases except
> PROT_NONE. In particular, mlock should not fail for PROT_WRITE regions
> (as in the blktrace case, which broke at 5ecfda0) or for PROT_EXEC
> regions (which seem to me like they were always broken).
>
> Please review. I am proposing this as a candidate for 2.6.38 inclusion,
> because of the behavior change with blktrace.

Signed-off-by: Michel Lespinasse <walken@google.com>

> diff --git a/mm/mlock.c b/mm/mlock.c
> index 13e81ee..c3924c7f 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -178,6 +178,13 @@ static long __mlock_vma_pages_range(struct vm_area_s=
truct *vma,
> =A0 =A0 =A0 =A0if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) =3D=3D VM_WRI=
TE)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0gup_flags |=3D FOLL_WRITE;
>
> + =A0 =A0 =A0 /*
> + =A0 =A0 =A0 =A0* We want mlock to succeed for regions that have any per=
missions
> + =A0 =A0 =A0 =A0* other than PROT_NONE.
> + =A0 =A0 =A0 =A0*/
> + =A0 =A0 =A0 if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 gup_flags |=3D FOLL_FORCE;
> +
> =A0 =A0 =A0 =A0if (vma->vm_flags & VM_LOCKED)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0gup_flags |=3D FOLL_MLOCK;

--=20
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.

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