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

[Chintan Pandya]

On 4/17/2018 8:39 AM, Anshuman Khandual wrote:
> On 04/16/2018 05:39 PM, Chintan Pandya wrote:
> > On 4/13/2018 5:31 PM, Anshuman Khandual wrote:
> > > 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
> > Right, I missed it. I plan to add below stub in v2.
> >
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -1124,15 +1124,15 @@ void vm_unmap_ram(const void *mem, unsigned int
> > count)
> >          BUG_ON(addr > VMALLOC_END);
> >          BUG_ON(!PAGE_ALIGNED(addr));
> >
> > -       debug_check_no_locks_freed(mem, size);
> > -
> >          if (likely(count <= VMAP_MAX_ALLOC)) {
> > +               debug_check_no_locks_freed(mem, size);
>
> It should have been 'va->va_start' instead of 'mem' in here but as
> said before it looks correct to me but I am not really sure.

vb_free() doesn't honor va->va_start. If mem is not va_start and
deliberate, one will provide proper size. And that should be okay
to do as per the code. So, I don't think this particular debug_check
should have passed va_start in args.

>

Chintan
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