Matthew Wilcox [off-list ref] wrote:

This is a read, not a write ... but we don't care about ki_pos being
updated, so that store can be conditioned on IOCB_SWAP being clear.
Or instead of storing directly to ki_pos, we take a pointer to ki_pos
and then redirect that pointer somewhere harmless.

But see also ext4_dio_read_iter(), for example.  That touches ki_filp after
starting the op.

David