On Tue, Jan 03, 2023 at 09:59:52AM +0100, Jiri Slaby wrote:
> On 26. 12. 22, 7:21, Deepak R Varma wrote:
> > The refcount_* APIs are designed to address known issues with the
> > atomic_t APIs for reference counting. They provide following distinct
> > advantages
> > - protect the reference counters from overflow/underflow
> > - avoid use-after-free errors
> > - provide improved memory ordering guarantee schemes
> > - neater and safer.
>
> Really? (see below)
>
> > --- a/drivers/tty/serial/dz.c
> > +++ b/drivers/tty/serial/dz.c
> ...
> > @@ -687,23 +686,19 @@ static int dz_map_port(struct uart_port *uport)
> > static int dz_request_port(struct uart_port *uport)
> > {
> > struct dz_mux *mux = to_dport(uport)->mux;
> > - int map_guard;
> > int ret;
> >
> > - map_guard = atomic_add_return(1, &mux->map_guard);
> > - if (map_guard == 1) {
> > - if (!request_mem_region(uport->mapbase, dec_kn_slot_size,
> > - "dz")) {
> > - atomic_add(-1, &mux->map_guard);
> > - printk(KERN_ERR
> > - "dz: Unable to reserve MMIO resource\n");
> > + refcount_inc(&mux->map_guard);
> > + if (refcount_read(&mux->map_guard) == 1) {
>
> This is now racy, right?
Hello Jiri,
I found this [1] commit which introduced similar transformation in a
neighbouring driver. Can you please comment how is this different from the
current patch proposal?
[1] commit ID: 22a33651a56f ("convert sbd_duart.map_guard from atomic_t to refcount_t")
On a side note, I have not been able to find an exact 1:1 map to the
atomic_add_result API. I am wondering should we have one?
Thank you,
./drv
Thank you,
./drv
>
> thanks,
> --
> js
> suse labs
>
