Am 09.01.2015 um 14:56 schrieb Peter Zijlstra: > On Fri, Jan 09, 2015 at 05:49:54AM -0800, Paul E. McKenney wrote: >>> That reminds me, I think the new conversion for stores will most likely >>> introduce silly arg bugs: >>> >>> - ACCESS_ONCE(a) = b; >>> + ASSIGN_ONCE(b, a); >> >> I was planning to do mine by hand for this sort of reason. >> >> Or are you thinking of something more subtle than the case where >> "b" is an unparenthesized comma-separated expression? > > I think he's revering to the wrong way around-ness of the thing. > > Its a bit of a mixed bag on assignments, but for instance > rcu_assign_pointer() takes them the right way around, as does > atomic_set(). > > So yes, I think the ASSIGN_ONCE() thing got the arguments the wrong way > around. > > We could maybe still change it, before its in too long ?
Linus initial proposal was inspired by put_user model which is (val, ptr) and I took that. As my focus was on avoiding the volatile bug, all my current conversions are READ_ONCE as no potential ASSIGN_ONCE user was done on a non-scalar type, so I have no first hand experience. I am fine with changing that, though, both ways have pros and cons. Last time I checked in Linus tree there was no ASSIGN_ONCE user. When we talk about changing the parameters it might make sense to also think about some comments from George Spelvin and consider a rename to WRITE_ONCE or STORE_ONCE (READ_ONCE --> LOAD_ONCE). Unfortunately there doesnt seem to be a variant that is fool proof (in the sense of Rustys guideline that a good interface cannot be used wrong). So any proposal in that regard would be very welcome. Christian -- 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/
