On Fri, Aug 31, 2018 at 08:58:39AM -0700, Dave Hansen wrote:

On 08/31/2018 08:48 AM, Yu-cheng Yu wrote:

quoted

To trigger a race in ptep_set_wrprotect(), we need to fork from one of
three pthread siblings.

Or do we measure only how much this affects fork?
If there is no racing, the effect should be minimal.

We don't need a race.

I think the cmpxchg will be slower, even without a race, than the code
that was there before.  The cmpxchg is a simple, straightforward
solution, but we're putting it in place of a plain memory write, which
is suboptimal.

Note quite, the clear_bit() is LOCK prefixed.