Function __vma_adjust() checks on *insert* to decide whether it is
necessary to remove_next/adjust_next. While it is more reasonable to do
the check on *expand* instead of on *insert*, since this is only necessary
when *expand* is non-NULL.
There are several users for __vma_adjust, let's classify them based on
the value of *insert*/*expand*:
caller | insert/expand
------------------------+-----------------
vma_merge | NULL/non-NULL
__split_vma | non-NULL/NULL
shift_arg_pages/mremap | NULL/NULL
To make this change, we need to make sure those non-NULL *insert* cases
wouldn't go into this if branch except vma_merge. There are two cases we
need to take care of: shift_arg_pages and mremap. Let's look at it one
by one.
For mremap, it is for sure we won't go into this if branch since
vma_adjust tries to expand the vma and the vma is expandable(the end
wouldn't interact with vma and next).
For shift_arg_pages, this case is a little tricky. Actually, for this
case, vma->vm_next should be NULL. Otherwise we would go into the branch
of "end < vma->vm_end" since we are shifting left. This means we would
expand the vma->vm_next by accident. Luckily, in current code, we won't
fall into this situation because shift_arg_pages only shift the stack
which is the highest one in virtual space.
To make the code more easy to understand(only vma_merge has a non-NULL
expand), and to make it handle the corner case(shift_arg_pages)
properly, let's do the check on *expand* instead of *insert*.
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 829897646a9c..ca31b405fbfa 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -706,7 +706,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
long adjust_next = 0;
int remove_next = 0;
- if (next && !insert) {
+ if (next && expand) {
struct vm_area_struct *exporter = NULL, *importer = NULL;
if (end >= next->vm_end) {
--
2.20.1 (Apple Git-117)
