linux-kernel - Re: [PATCH 2/4] mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(,MLOCK

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Message-ID: <20160830113644.GB32187@node.shutemov.name>
Date:   Tue, 30 Aug 2016 14:36:44 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     wei.guo.simon@...il.com
Cc:     linux-mm@...ck.org, Alexey Klimov <klimov.linux@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric B Munson <emunson@...mai.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>, Shuah Khan <shuah@...nel.org>,
        Thierry Reding <treding@...dia.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 2/4] mm: mlock: avoid increase mm->locked_vm on mlock()
 when already mlock2(,MLOCK_ONFAULT)

On Tue, Aug 30, 2016 at 06:59:39PM +0800, wei.guo.simon@...il.com wrote:
> From: Simon Guo <wei.guo.simon@...il.com>
> 
> When one vma was with flag VM_LOCKED|VM_LOCKONFAULT (by invoking
> mlock2(,MLOCK_ONFAULT)), it can again be populated with mlock() with
> VM_LOCKED flag only.
> 
> There is a hole in mlock_fixup() which increase mm->locked_vm twice even
> the two operations are on the same vma and both with VM_LOCKED flags.
> 
> The issue can be reproduced by following code:
> mlock2(p, 1024 * 64, MLOCK_ONFAULT); //VM_LOCKED|VM_LOCKONFAULT
> mlock(p, 1024 * 64);  //VM_LOCKED
> Then check the increase VmLck field in /proc/pid/status(to 128k).
> 
> When vma is set with different vm_flags, and the new vm_flags is with
> VM_LOCKED, it is not necessarily be a "new locked" vma.  This patch
> corrects this bug by prevent mm->locked_vm from increment when old
> vm_flags is already VM_LOCKED.
> 
> Signed-off-by: Simon Guo <wei.guo.simon@...il.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov