2015-11-12 18:17 GMT+03:00 Jerome Marchand <jmarchan@xxxxxxxxxx>:
> Commit 71394fe50146 ("mm: vmalloc: add flag preventing guard hole
> allocation") missed a spot. Currently remove_vm_area() decreases
> vm->size to remove the guard hole page, even when it isn't present.
> This patch only decreases vm->size when VM_NO_GUARD isn't set.
>
> Signed-off-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
> ---
> mm/vmalloc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d045634..1388c3d 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1443,7 +1443,8 @@ struct vm_struct *remove_vm_area(const void *addr)
> vmap_debug_free_range(va->va_start, va->va_end);
> kasan_free_shadow(vm);
> free_unmap_vmap_area(va);
> - vm->size -= PAGE_SIZE;
> + if (!(vm->flags & VM_NO_GUARD))
> + vm->size -= PAGE_SIZE;
>
I'd fix this in another way. I think that remove_vm_area() shouldn't
change vm's size, IMO it doesn't make sense.
The only caller who cares about vm's size after removing is __vunmap():
area = remove_vm_area(addr);
....
debug_check_no_locks_freed(addr, area->size);
debug_check_no_obj_freed(addr, area->size);
We already have proper get_vm_area_size() helper which takes
VM_NO_GUARD into account.
So I think we should use that helper for debug_check_no_*() and just
remove 'vm->size -= PAGE_SIZE;' line
from remove_vm_area()
> return vm;
> }
> --
> 2.4.3
>
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