On Sat, 21 May 2016, Peter Zijlstra wrote:
On Fri, May 20, 2016 at 05:48:39PM -0700, Davidlohr Bueso wrote:
On Fri, 20 May 2016, Linus Torvalds wrote:
>Oh, I definitely agree on the stable part, and yes, the "splt things
>up" model should come later if people agree that it's a good thing.
The backporting part is quite nice, yes, but ultimately I think I prefer
Linus' suggestion making things explicit, as opposed to consulting the spinlock
implying barriers. I also hate to have an smp_mb() (particularly for
spin_is_locked)
given that we are not optimizing for the common case (regular mutual excl).
I'm confused; we _are_ optimizing for the common case. spin_is_locked()
is very unlikely to be used. And arguably should be used less in favour
of lockdep_assert_held().
Indeed we are.
But by 'common case' I was really thinking about spin_is_locked() vs
spin_wait_unlock().
The former being the more common of the two, and the one which mostly will
_not_ be used
for lock correctness purposes, hence it doesn't need that new smp_mb. Hence
allowing users
to explicitly set the ordering needs (ie spin_lock_synchronize()) seems like
the better
long term alternative. otoh, with your approach all such bugs are automatically
fixed :)
Thanks,
Davidlohr
