* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> [241031 16:48]:
> 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?
Sounds good. I guess I should have waited longer for a v2.
>
> --- 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;
> _
>
