From: Vineet Gupta <vineet.gupta1@xxxxxxxxxxxx> Subject: include/linux/bitops.h: set_mask_bits() to return old value | > 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 Link: http://lkml.kernel.org/r/1548275584-18096-4-git-send-email-vgupta@xxxxxxxxxxxx Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Reviewed-by: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx> Acked-by: Will Deacon <will.deacon@xxxxxxx> Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jani Nikula <jani.nikula@xxxxxxxxx> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Theodore Ts'o <tytso@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/include/linux/bitops.h~bitopsh-set_mask_bits-to-return-old-value +++ a/include/linux/bitops.h @@ -246,7 +246,7 @@ static __always_inline void __assign_bit new__ = (old__ & ~mask__) | bits__; \ } while (cmpxchg(ptr, old__, new__) != old__); \ \ - new__; \ + old__; \ }) #endif _
