On Thu, Jan 10, 2019 at 04:26:27PM -0800, Vineet Gupta wrote: > | > Also, set_mask_bits is used in fs quite a bit and we can possibly come up > | > with a generic llsc based implementation (w/o the cmpxchg loop) > | > | May I also suggest changing the return value of set_mask_bits() to old. > | > | You can compute the new value given old, but you cannot compute the old > | value given new, therefore old is the better return value. Also, no > | current user seems to use the return value, so changing it is without > | risk. > > Link: http://lkml.kernel.org/g/20150807110955.GH16853@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Jani Nikula <jani.nikula@xxxxxxxxx> > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Will Deacon <will.deacon@xxxxxxx> > Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx> > --- > include/linux/bitops.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index 705f7c442691..602af23b98c7 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -246,7 +246,7 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr, > new__ = (old__ & ~mask__) | bits__; \ > } while (cmpxchg(ptr, old__, new__) != old__); \ > \ > - new__; \ > + old__; \ > }) > #endif Acked-by: Will Deacon <will.deacon@xxxxxxx> May also explain why no in-tree users appear to use the return value! Will
