On 02/01/2013 02:10 PM, Johannes Weiner wrote:
The fact that mlock calls get_user_pages, and get_user_pages might
call mlock when expanding a stack looks like a potential recursion.
Why expand stack need call mlock? I can't find it in the codes, could
you point out to me?
However, mlock makes sure the requested range is already contained
within a vma, so no stack expansion will actually happen from mlock.
Should this ever change: the stack expansion mlocks only the newly
expanded range and so will not result in recursive expansion.
Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
mm/mlock.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/mlock.c b/mm/mlock.c
index b1647fb..78c4924 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -185,6 +185,10 @@ long __mlock_vma_pages_range(struct vm_area_struct *vma,
if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
gup_flags |= FOLL_FORCE;
+ /*
+ * We made sure addr is within a VMA, so the following will
+ * not result in a stack expansion that recurses back here.
+ */
return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
NULL, NULL, nonblocking);
}
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