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

[Chintan Pandya]

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);
                vb_free(mem, size);
                return;
        }

        va = find_vmap_area(addr);
        BUG_ON(!va);
+       debug_check_no_locks_freed(va->va_start, (va->va_end - 
va->va_start));
        free_unmap_vmap_area(va);
 }
 EXPORT_SYMBOL(vm_unmap_ram);


> 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.

Chintan
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