On Mon, Mar 18, 2019 at 08:20:22PM -0700, Matthew Wilcox wrote:
> On Mon, Mar 18, 2019 at 09:56:05PM +0530, Souptick Joarder wrote:
> > >> mm/memory.c:3968:21: sparse: incorrect type in assignment (different
> > >> base types) @@ expected restricted vm_fault_t [usertype] ret @@
> > >> got e] ret @@
> > mm/memory.c:3968:21: expected restricted vm_fault_t [usertype] ret
> > mm/memory.c:3968:21: got int
>
> I think this may be a sparse bug.
>
> Compare:
>
> +++ b/mm/memory.c
> @@ -3964,6 +3964,9 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> if (flags & FAULT_FLAG_USER)
> mem_cgroup_enter_user_fault();
>
> + ret = 0;
> + ret = ({ BUG(); 0; });
> + ret = 1;
> if (unlikely(is_vm_hugetlb_page(vma)))
> ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
> else
>
> ../mm/memory.c:3968:13: sparse: warning: incorrect type in assignment (different base types)
> ../mm/memory.c:3968:13: sparse: expected restricted vm_fault_t [assigned] [usertype] ret
> ../mm/memory.c:3968:13: sparse: got int
> ../mm/memory.c:3969:13: sparse: warning: incorrect type in assignment (different base types)
> ../mm/memory.c:3969:13: sparse: expected restricted vm_fault_t [assigned] [usertype] ret
> ../mm/memory.c:3969:13: sparse: got int
>
> vm_fault_t is __bitwise:
>
> include/linux/mm_types.h:typedef __bitwise unsigned int vm_fault_t;
>
> so simply assigning 0 to ret should work (and does on line 3967), but
> sparse doesn't seem to like it as part of a ({ .. }) expression.
This is the expected behaviour. The constant 0 is magic regarding
bitwise types but ({ ...; 0; }) is not, it is just an ordinary expression
of type 'int'.
So, IMHO, Souptick's patch is the right thing to do.
Best regards,
-- Luc Van Oostenryck
