mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(,MLOCK_ONFAULT)

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/[email protected]
Signed-off-by: Simon Guo <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Cc: Alexey Klimov <[email protected]>
Cc: Eric B Munson <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Simon Guo <[email protected]>
Cc: Thierry Reding <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/mlock.c b/mm/mlock.c
index b1fec89bd1c526c70766e034d1f22cdc68f1e6c5..145a4258ddbc775d1d2acf133a21b83280a8f282 100644 (file)
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -516,6 +516,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
        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))
@@ -550,6 +551,8 @@ 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;
 
        /*