[PATCH 2/2] ARM: include: asm: use 'int' instead of 'unsigned long' for normal register variables within atomic.h

Chen Gang gang.chen at asianux.com
Fri Oct 4 19:55:18 EDT 2013

On 10/04/2013 11:42 PM, Will Deacon wrote:
> On Fri, Oct 04, 2013 at 04:37:42PM +0100, Will Deacon wrote:
>> On Fri, Oct 04, 2013 at 10:51:56AM +0100, Chen Gang wrote:
>>> On 10/04/2013 12:32 AM, Will Deacon wrote:
>>>> The problem with arm64 is that we're using *unsigned long* for 32-bit
>>>> clear_mask, which is definitely wrong because it's 64-bit (another patch to
>>>> fix this!).
>>> At least, that is not a bug.
>> Sure it is. What if the adjacent 32-bit value was being accessed by another
>> CPU under a spinlock?
> (Oh, ok, that would still work on arm because of the way the exclusive
> monitor is implemented, but we shouldn't rely on that).

Hmm... in my opinion, we need divide atomic_*_mask() into 32-bit and
64-bit versions. We already have demands to only use 32-bit value to
express mask (can save size), and may have demands to use 64-bit too.

If so, can easily standard all atomic_*_mask() which are in asm-generic
and various architectures: use atomic_*_mask() for 32-bit mask, and use
atomic64_*_mask() for 64-bit mask (can delayed before get real demands).

Since it is about API, so it is related with asm-generic and all other
architectures interfaces, it is better to consider about them firstly
before the fix under arm64.

And also, excuse me, I am not quite familiar with "exclusive monitor",
could you please provide more details about it?

> Will

Chen Gang

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