Re: [RFC] Avoid mutex starvation when optimistic spinning is disabled

From: Davidlohr Bueso
Date: Fri Jul 22 2016 - 15:26:21 EST

On Fri, 22 Jul 2016, Imre Deak wrote:

On Fri, 2016-07-22 at 11:03 -0700, Davidlohr Bueso wrote:
On Fri, 22 Jul 2016, Waiman Long wrote:

> I think making mutex_trylock() fail maybe a bit too far. Do we
> really
> have any real workload that cause starvation problem  because of
> that.
> Code that does mutex_trylock() in a loop can certainly cause lock
> starvation, but it is not how mutex_trylock() is supposed to be
> used.
> We can't build in safeguard for all the possible abuses of the
> mutex
> APIs.

True, and that's actually why I think that 'fixing' the
is a bit too far in the first place: most of the archs that will care
this already have ARCH_SUPPORTS_ATOMIC_RMW. The extra code for
dealing with
this is not worth it imo.

SPIN_ON_OWNER is also disabled in case of DEBUG_MUTEXES, which is the
config where I wanted to avoid starvation in the first place.

Well yes, but know of course that that option is even less common than
archs with non atomic Rmw.