Re: WARNING: at mm/mremap.c:211 move_page_tables in i386

Kirill A. Shutemov
2020-07-14T07:33:07Z

On Sun, Jul 12, 2020 at 03:58:06PM -0700, Linus Torvalds wrote:
> Anybody else have any opinions?

Maybe we just shouldn't allow move_normal_pmd() if ranges overlap?

Other option: pass 'overlaps' down to move_normal_pmd() and only WARN() if
see establised PMD without overlaps being true.

Untested patch:

diff --git a/mm/mremap.c b/mm/mremap.c
index 5dd572d57ca9..e33fcee541fe 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -245,6 +245,18 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
unsigned long extent, next, old_end;
struct mmu_notifier_range range;
pmd_t *old_pmd, *new_pmd;
+ bool overlaps;
+
+ /*
+ * shift_arg_pages() can call move_page_tables() on overlapping ranges.
+ * In this case we cannot use move_normal_pmd() because destination pmd
+ * might be established page table: move_ptes() doesn't free page
+ * table.
+ */
+ if (old_addr > new_addr)
+ overlaps = old_addr - new_addr < len;
+ else
+ overlaps = new_addr - old_addr < len;

old_end = old_addr + len;
flush_cache_range(vma, old_addr, old_end);
@@ -282,7 +294,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
split_huge_pmd(vma, old_pmd, old_addr);
if (pmd_trans_unstable(old_pmd))
continue;
- } else if (extent == PMD_SIZE) {
+ } else if (!overlaps && extent == PMD_SIZE) {
#ifdef CONFIG_HAVE_MOVE_PMD
/*
* If the extent is PMD-sized, try to speed the move by
--
Kirill A. Shutemov