On Wed, Mar 28, 2018 at 08:51:35AM +1100, Benjamin Herrenschmidt wrote: > On Tue, 2018-03-27 at 15:13 +0200, Andrea Parri wrote: > > > > > > So unless it's very performance sensitive, I'd rather have things like > > > spin_is_locked be conservative by default and provide simpler ordering > > > semantics. > > > > Well, it might not be "very performance sensitive" but allow me to say > > that "40+ SYNCs in stuff like BUG_ON or such" is sadness to my eyes ;), > > In the fast path or the trap case ? Because the latter doesn't matter > at all...
Both: you must execute the sync "before" issuing the load of lock.slock. > > > especially when considered that our "high level API" provides means to > > avoid this situation (e.g., smp_mb__after_spinlock(); BTW, if you look > > at architectures for which this macro is "non-trivial", you can get an > > idea of the architectures which "wouldn't work"; of course, x86 is not > > among these). Yes, we do appear to have different views on what is to > > be considered the "simpler ordering semantics". I'm willing to change > > mine _as soon as_ this gets documented: would you be willing to send a > > patch (on the lines of my [1]) to describe/document such semantics? > > Not really :-) Just expressing an opinion. I don't fully object to your > approach, just saying it's open for debate. Always (open for debate). I'm sending a v2 of this series shortly, integrating some feedback; I prefer to keep this patch in the series (feel free to ignore). Andrea > > At this point, I have too many other things to chase to follow up too > much on this. > > Cheers, > Ben. >
