linux-kernel - [PATCH 4.4 55/91] mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(,MLOCK

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Date:   Tue, 11 Dec 2018 16:41:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Simon Guo <wei.guo.simon@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Alexey Klimov <klimov.linux@...il.com>,
        Eric B Munson <emunson@...mai.com>,
        Geert Uytterhoeven <geert@...ux-m68k.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>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rafael David Tinoco <rafael.tinoco@...aro.org>
Subject: [PATCH 4.4 55/91] mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(,MLOCK_ONFAULT)

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Simon Guo <wei.guo.simon@...il.com>

commit b155b4fde5bdde9fed439cd1f5ea07173df2ed31 upstream.

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.

Link: http://lkml.kernel.org/r/1472554781-9835-3-git-send-email-wei.guo.simon@gmail.com
Signed-off-by: Simon Guo <wei.guo.simon@...il.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Alexey Klimov <klimov.linux@...il.com>
Cc: Eric B Munson <emunson@...mai.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Simon Guo <wei.guo.simon@...il.com>
Cc: Thierry Reding <treding@...dia.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Rafael David Tinoco <rafael.tinoco@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/mlock.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -504,6 +504,7 @@ static int mlock_fixup(struct vm_area_st
 	int nr_pages;
 	int ret = 0;
 	int lock = !!(newflags & VM_LOCKED);
+	vm_flags_t old_flags = vma->vm_flags;

 	if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
 	    is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
@@ -538,6 +539,8 @@ success:
 	nr_pages = (end - start) >> PAGE_SHIFT;
 	if (!lock)
 		nr_pages = -nr_pages;
+	else if (old_flags & VM_LOCKED)
+		nr_pages = 0;
 	mm->locked_vm += nr_pages;

 	/*