Re: [PATCH 00/16] mm: prepare for converting vm->vm_flags to 64-bit

Konstantin Khlebnikov
2012-03-22T22:05:27Z

Andrew Morton wrote:
> On Thu, 22 Mar 2012 21:28:11 +0000
> Al Viro<viro@ZenIV.linux.org.uk> wrote:
>
>> On Thu, Mar 22, 2012 at 02:26:47PM -0700, Andrew Morton wrote:
>>> It would be nice to find some way of triggering compiler warnings or
>>> sparse warnings if someone mixes a 32-bit type with a vm_flags_t. Any
>>> thoughts on this?
>>>
>>> (Maybe that's what __nocast does, but Documentation/sparse.txt doesn't
>>> describe it)
>>
>> Use __bitwise for that - check how gfp_t is handled.
>
> So what does __nocast do?

Actually it forbid any non-forced casts, but its implementation in sparse seems buggy:
__nocast generates some strange false positives. For example it sometimes forgot about
type attributes in function arguments, I saw this for vm_flags argument in ksm_madvise().
I can reproduce this bug, if somebody interested.