Re: [PATCH 2/2] mm: vmalloc: Pass proper vm_start into debugobjects

From: Anshuman Khandual
Date: Fri Apr 13 2018 - 08:02:10 EST


On 04/13/2018 05:03 PM, Chintan Pandya wrote:
> Client can call vunmap with some intermediate 'addr'
> which may not be the start of the VM area. Entire
> unmap code works with vm->vm_start which is proper
> but debug object API is called with 'addr'. This
> could be a problem within debug objects.
>
> Pass proper start address into debug object API.
>
> Signed-off-by: Chintan Pandya <cpandya@xxxxxxxxxxxxxx>
> ---
> mm/vmalloc.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 9ff21a1..28034c55 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1526,8 +1526,8 @@ static void __vunmap(const void *addr, int deallocate_pages)
> return;
> }
>
> - debug_check_no_locks_freed(addr, get_vm_area_size(area));
> - debug_check_no_obj_freed(addr, get_vm_area_size(area));
> + debug_check_no_locks_freed(area->addr, get_vm_area_size(area));
> + debug_check_no_obj_freed(area->addr, get_vm_area_size(area));

This kind of makes sense to me but I am not sure. We also have another
instance of this inside the function vm_unmap_ram() where we call for
debug on locks without even finding the vmap_area first. But it is true
that in both these functions the vmap_area gets freed eventually. Hence
the entire mapping [va->va_start --> va->va_end] gets unmapped. Sounds
like these debug functions should have the entire range as argument.
But I am not sure and will seek Michal's input on this.