On Fri, Nov 25, 2016 at 10:07 AM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> On Fri, Nov 25, 2016 at 09:52:50AM -0800, Linus Torvalds wrote:
>> READ/WRITE_ONCE() are atomic *WHEN*THAT*IS*POSSIBLE*.
>
>> But sometimes it's not going to be atomic.
>
> That's the problem.
It has never really been much of a problem, and quite frankly, the
solution would never be to add _another_ crazy new function that will
just confuse everybody.
If you have code that depends on atomicity of READ_ONCE() and friends,
then you should add the appropriate built-time assert to *your* code.
Not to some random generic function that others care about and that
others do _not_ have problems with.
So if you have a data structure in virtio that is
architecture-dependent and might not be a word size, you add the
BUILD_BUG_ON(sizeof(mytype) > sizeof(long));
or whatever. With a big comment saying "this needs to actually fit in
a single register so that we can do atomic accesses".
You do not screw it up for everybody else.
Linus
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