Re: [PATCHv2] mm: Fix warning in move_normal_pmd()

[Linus Torvalds <torvalds@linux-foundation.org>]

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On Wed, Jul 15, 2020 at 3:57 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> But now I've screwed it up twice, and have a splitting headache, so
> rather than stare at this cross-eyed, I'll take a break and hope that
> somebody more competent than me looks at the code.

I lied. I had a couple of pending pulls, so I couldn't go lie down
anyway, so I tried to take another look.

It *might* be as simple as this incremetal thing on top, but then I
think that code will no longer trigger on the stack movement case at
all, since there we don't work with the whole vma.

So if we want that to work, we'd have to fix that up too.

And this might be broken anyway. My track record isn't looking so hot right now.

                  Linus

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diff --git a/mm/mremap.c b/mm/mremap.c
index 614b4fffed1d..6c3df022ff64 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -243,6 +243,9 @@ static inline void try_to_align_start(unsigned long *len,
 	struct vm_area_struct *old, unsigned long *old_addr,
 	struct vm_area_struct *new, unsigned long *new_addr)
 {
+	if (*old_addr > old->vm_start)
+		return;
+
 	if (ADDR_BEFORE_PREV(*old_addr & PMD_MASK, old))
 		return;
 
@@ -270,6 +273,9 @@ static inline void try_to_align_end(unsigned long *len,
 	struct vm_area_struct *old, unsigned long *old_addr,
 	struct vm_area_struct *new, unsigned long *new_addr)
 {
+	if (*old_addr < old->vm_end)
+		return;
+
 	if (ADDR_AFTER_NEXT(*old_addr + *len, old))
 		return;