| Message ID | 20200917224722.54428-1-richard.weiyang@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/mmap: do the check on expand instead of on insert | expand |
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) {
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@linux.alibaba.com> --- mm/mmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)