Re: [PATCH] fs: inode_set_flags() replace opencoded set_mask_bits()

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Aug 07, 2015 at 12:25:04PM +0530, Vineet Gupta wrote:
> It seems that 5f16f3225b0624 and 00a1a053ebe5, both with same commitlog
> ("ext4: atomically set inode->i_flags in ext4_set_inode_flags()")
> introduced the set_mask_bits API, but somehow missed not using it in
> ext4 in the end
> 
> 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.