Messages in this thread | | | Date | Tue, 10 Jan 2023 11:49:24 +0530 | From | Deepak R Varma <> | Subject | Re: [PATCH v4 1/2] tty: serial: dz: convert atomic_* to refcount_* APIs for map_guard |
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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 >
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