From: Simon Guo <wei.guo.si...@gmail.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.si...@gmail.com>
---
mm/mlock.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/mlock.c b/mm/mlock.c
index 9283187..df29aad 100644
--- 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;
/*
--
1.8.3.1
