Re: [PATCH v2] locking/rwsem: Add reader-owned state to the owner field

[Peter Zijlstra]

On Wed, May 18, 2016 at 10:26:06AM -0700, Paul E. McKenney wrote:
> On Wed, May 18, 2016 at 01:05:55PM +0200, Peter Zijlstra wrote:

> > Alternatively, could we try and talk to our GCC friends to make sure GCC
> > doesn't tear loads/stores irrespective of what the C language spec
> > allows?
> 
> Interestingly enough, they used to make that guarantee, but removed it
> when C11 showed up.

Did someone tell them this was a regression and have them fix it? They
can't just change things like this.

> Me, I would feel better explicitly telling the compiler what I needed.
> It is all too easy for bugs to slip in otherwise, especially when the
> gcc guys are adding exciting new optimizations.

GCC guys (as opposed to the language guys) should be far more amenable
to our needs, and I don't think they want to break the kernel any more
than we do.