On Mon, 2014-06-02 at 22:05 +0200, Peter Zijlstra wrote: > On Mon, Jun 02, 2014 at 01:33:34PM -0400, Waiman Long wrote: > > On 06/02/2014 12:30 PM, Peter Zijlstra wrote: > > >On Mon, Jun 02, 2014 at 06:25:25PM +0200, Peter Zijlstra wrote: > > >>I'm almost inclined to just exclude parisc from using opt spinning. > > >> > > >>That said, this patch still doesn't address the far more interesting > > >>problem of actually finding these issues for these few weird archs. > > >So why do these archs provide xchg() and cmpxchg() at all? Wouldn't it > > >be much simpler if archs that cannot sanely do this, not provide these > > >primitives at all? > > > > I believe xchg() and cmpxchg() are used in quite a number of places within > > the generic kernel code. So kernel compilation will fail if those APIs > > aren't provided by an architecture. > > Yep.. so this is going to be painful for a while. But given their > (parisc, sparc32, metag-lock1) constraints, who knows how many of those > uses are actually broken. > > So the question is, do you prefer subtly broken code or hard compile > fails? Me, I go for the compile fail.
The failure is only when a variable that will have an atomic exchange done on it is updated by a simple operation. To do this properly, we'd probably need an update macro we could supply the locking to, and a way of marking the variable to get the compiler to cause a build error if it was ever updated improperly, but that's starting to look very similar to Mikulas' proposal. James -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
