On Thu, 31 Oct 2024 15:36:08 -0400 "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx> wrote:
> From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
>
> There have been no reported infinite loops in the tree, but checking the
> detection of an infinite loop during validation is simple enough. Add
> the detection to the validate_mm() function so that error reports are
> clear and don't just report stalls.
>
> This does not protect against internal maple tree issues, but it does
> detect too many vmas being returned from the tree.
>
> The variance of +10 is to allow for the debugging output to be more useful for
> nearly correct counts. In the event of more than 10 over the map_count, the
> count will be set to -1 for easier identification of a potential infinite loop.
>
> Note that the mmap lock is held to ensure a consistent tree state during the
> validation process.
>
> ...
>
> +++ b/mm/vma.c
> @@ -615,7 +615,10 @@ void validate_mm(struct mm_struct *mm)
> anon_vma_unlock_read(anon_vma);
> }
> #endif
> - i++;
> + if (++i > mm->map_count + 10) {
> + i = -1;
> + break;
> + }
> }
> if (i != mm->map_count) {
> pr_emerg("map_count %d vma iterator %d\n", mm->map_count, i);
It might be helpful to tell readers what's going on here?
--- a/mm/vma.c~vma-detect-infinite-loop-in-vma-tree-fix
+++ a/mm/vma.c
@@ -615,6 +615,7 @@ void validate_mm(struct mm_struct *mm)
anon_vma_unlock_read(anon_vma);
}
#endif
+ /* Check for a infinite loop */
if (++i > mm->map_count + 10) {
i = -1;
break;
_
