linux-kernel - Re: [PATCH] include/linux/hugetlb.h: Convert to use vm_fault

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Date:   Mon, 18 Mar 2019 20:20:22 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     akpm@...ux-foundation.org, mike.kravetz@...cle.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-sparse@...r.kernel.org
Subject: Re: [PATCH] include/linux/hugetlb.h: Convert to use vm_fault_t

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.