On Fri, 23 Apr 2021 11:53:06 -0400 Eric Farman <farman@xxxxxxxxxxxxx> wrote: > > > > Is in your opinion the vfio-ccw kernel module data race free with > > this > > series applied? > > I have no further concerns. I take this for a "yes, in my opinion it is data race free". Please explain me, how do we synchronize access to a) private->state b) cp->initialized? Asuming we both use the definition from the C standard, the multiple threads potentially concurrently accessing private->state or cp->initialized are not hard to find. For the former you can take vfio_ccw_sch_io_todo() (has both a read and a write, and runs from the workqueue) and fsm_io_request() (has both read and write). I guess the accesses from fsm_io_request() are all with the io_mutex held, but the accesses form vfio_ccw_sch_io_todo() are not with the io_mutex held AFAICT. And the same is true for the latter with the difference that vfio_ccw_sch_io_todo() manipulates cp->initialized via cp_update_scsw() and cp_free(). These are either data races, or I'm missing something. Let me also note that C programs data races are bad news, because of undefined behavior. Regards, Halil
