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/[email protected] > Suggested-by: Peter Zijlstra <[email protected]> > Cc: Miklos Szeredi <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Jani Nikula <[email protected]> > Cc: Chris Wilson <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Will Deacon <[email protected]> > Signed-off-by: Vineet Gupta <[email protected]> > --- > 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 <[email protected]> May also explain why no in-tree users appear to use the return value! Will
