tty: serial: dz: convert atomic_* to refcount_*

[PATCH 2/2] tty: serial: dz: convert atomic_* to refcount_* APIs for irq_guard

Posted by Deepak R Varma 2 years, 8 months ago

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.
Hence, replace the atomic_* APIs by their equivalent refcount_t
API functions.

This patch proposal address the following warnings generated by
the atomic_as_refcounter.cocci coccinelle script
atomic_add_return(-1, ...)

Signed-off-by: Deepak R Varma <drv@mailo.com>
---
Please Note:
   1. The patch is compile tested using dec_station.defconfig for MIPS architecture.
   2. This patch should be applied after patch 1/2 of this series due to
      dependency.

Changes in v3:
   1. Include the individual patches in a series and highlight dependency.
      Feedback provided by gregkh@linuxfoundation.org

Changes in v2:
   1. Separate the combined change into one variable per patch as
      suggested by gregkh@linuxfoundation.org


 drivers/tty/serial/dz.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/serial/dz.c b/drivers/tty/serial/dz.c
index b70edc248f8b..0aa59a9beeb7 100644
--- a/drivers/tty/serial/dz.c
+++ b/drivers/tty/serial/dz.c
@@ -46,7 +46,6 @@
 #include <linux/tty.h>
 #include <linux/tty_flip.h>

-#include <linux/atomic.h>
 #include <linux/refcount.h>
 #include <linux/io.h>
 #include <asm/bootinfo.h>
@@ -77,7 +76,7 @@ struct dz_port {
 struct dz_mux {
 	struct dz_port		dport[DZ_NB_PORT];
 	refcount_t		map_guard;
-	atomic_t		irq_guard;
+	refcount_t		irq_guard;
 	int			initialised;
 };

@@ -400,18 +399,16 @@ static int dz_startup(struct uart_port *uport)
 	struct dz_port *dport = to_dport(uport);
 	struct dz_mux *mux = dport->mux;
 	unsigned long flags;
-	int irq_guard;
 	int ret;
 	u16 tmp;

-	irq_guard = atomic_add_return(1, &mux->irq_guard);
-	if (irq_guard != 1)
+	refcount_inc(&mux->irq_guard);
+	if (refcount_read(&mux->irq_guard) != 1)
 		return 0;

-	ret = request_irq(dport->port.irq, dz_interrupt,
-			  IRQF_SHARED, "dz", mux);
+	ret = request_irq(dport->port.irq, dz_interrupt, IRQF_SHARED, "dz", mux);
 	if (ret) {
-		atomic_add(-1, &mux->irq_guard);
+		refcount_dec(&mux->irq_guard);
 		printk(KERN_ERR "dz: Cannot get IRQ %d!\n", dport->port.irq);
 		return ret;
 	}
@@ -441,15 +438,13 @@ static void dz_shutdown(struct uart_port *uport)
 	struct dz_port *dport = to_dport(uport);
 	struct dz_mux *mux = dport->mux;
 	unsigned long flags;
-	int irq_guard;
 	u16 tmp;

 	spin_lock_irqsave(&dport->port.lock, flags);
 	dz_stop_tx(&dport->port);
 	spin_unlock_irqrestore(&dport->port.lock, flags);

-	irq_guard = atomic_add_return(-1, &mux->irq_guard);
-	if (!irq_guard) {
+	if (refcount_dec_and_test(&mux->irq_guard)) {
 		/* Disable interrupts.  */
 		tmp = dz_in(dport, DZ_CSR);
 		tmp &= ~(DZ_RIE | DZ_TIE);
--
2.34.1

Re: [PATCH v4 2/2] tty: serial: dz: convert atomic_* to refcount_* APIs for irq_guard

Posted by Jiri Slaby 2 years, 8 months ago

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.
> Hence, replace the atomic_* APIs by their equivalent refcount_t
> API functions.
> 
> This patch proposal address the following warnings generated by
> the atomic_as_refcounter.cocci coccinelle script
> atomic_add_return(-1, ...)
...
> --- a/drivers/tty/serial/dz.c
> +++ b/drivers/tty/serial/dz.c
...
> @@ -400,18 +399,16 @@ static int dz_startup(struct uart_port *uport)
>   	struct dz_port *dport = to_dport(uport);
>   	struct dz_mux *mux = dport->mux;
>   	unsigned long flags;
> -	int irq_guard;
>   	int ret;
>   	u16 tmp;
> 
> -	irq_guard = atomic_add_return(1, &mux->irq_guard);
> -	if (irq_guard != 1)
> +	refcount_inc(&mux->irq_guard);
> +	if (refcount_read(&mux->irq_guard) != 1)
>   		return 0;
> 
> -	ret = request_irq(dport->port.irq, dz_interrupt,
> -			  IRQF_SHARED, "dz", mux);
> +	ret = request_irq(dport->port.irq, dz_interrupt, IRQF_SHARED, "dz", mux);

How is this related to the above described change?

-- 
js
suse labs

Re: [PATCH v4 2/2] tty: serial: dz: convert atomic_* to refcount_* APIs for irq_guard

Posted by Deepak R Varma 2 years, 8 months ago

On Tue, Jan 03, 2023 at 10:00:48AM +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.
> > Hence, replace the atomic_* APIs by their equivalent refcount_t
> > API functions.
> >
> > This patch proposal address the following warnings generated by
> > the atomic_as_refcounter.cocci coccinelle script
> > atomic_add_return(-1, ...)
> ...
> > --- a/drivers/tty/serial/dz.c
> > +++ b/drivers/tty/serial/dz.c
> ...
> > @@ -400,18 +399,16 @@ static int dz_startup(struct uart_port *uport)
> >   	struct dz_port *dport = to_dport(uport);
> >   	struct dz_mux *mux = dport->mux;
> >   	unsigned long flags;
> > -	int irq_guard;
> >   	int ret;
> >   	u16 tmp;
> >
> > -	irq_guard = atomic_add_return(1, &mux->irq_guard);
> > -	if (irq_guard != 1)
> > +	refcount_inc(&mux->irq_guard);
> > +	if (refcount_read(&mux->irq_guard) != 1)
> >   		return 0;
> >
> > -	ret = request_irq(dport->port.irq, dz_interrupt,
> > -			  IRQF_SHARED, "dz", mux);
> > +	ret = request_irq(dport->port.irq, dz_interrupt, IRQF_SHARED, "dz", mux);
>
> How is this related to the above described change?

No, it is not. My apologies. I must have joined the lines for improved readability
and forgot to revert. I will restore this in next revision based on the feedback
on the other patch of this series. OR I can include this change in the current
change log as a "while at it..." statement. Would you advise me?

Thank you,
./drv

>
> --
> js
> suse labs
>

Re: [PATCH v4 2/2] tty: serial: dz: convert atomic_* to refcount_* APIs for irq_guard

Posted by Greg Kroah-Hartman 2 years, 8 months ago

On Tue, Jan 03, 2023 at 03:39:17PM +0530, Deepak R Varma wrote:
> On Tue, Jan 03, 2023 at 10:00:48AM +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.
> > > Hence, replace the atomic_* APIs by their equivalent refcount_t
> > > API functions.
> > >
> > > This patch proposal address the following warnings generated by
> > > the atomic_as_refcounter.cocci coccinelle script
> > > atomic_add_return(-1, ...)
> > ...
> > > --- a/drivers/tty/serial/dz.c
> > > +++ b/drivers/tty/serial/dz.c
> > ...
> > > @@ -400,18 +399,16 @@ static int dz_startup(struct uart_port *uport)
> > >   	struct dz_port *dport = to_dport(uport);
> > >   	struct dz_mux *mux = dport->mux;
> > >   	unsigned long flags;
> > > -	int irq_guard;
> > >   	int ret;
> > >   	u16 tmp;
> > >
> > > -	irq_guard = atomic_add_return(1, &mux->irq_guard);
> > > -	if (irq_guard != 1)
> > > +	refcount_inc(&mux->irq_guard);
> > > +	if (refcount_read(&mux->irq_guard) != 1)
> > >   		return 0;
> > >
> > > -	ret = request_irq(dport->port.irq, dz_interrupt,
> > > -			  IRQF_SHARED, "dz", mux);
> > > +	ret = request_irq(dport->port.irq, dz_interrupt, IRQF_SHARED, "dz", mux);
> >
> > How is this related to the above described change?
> 
> No, it is not. My apologies. I must have joined the lines for improved readability
> and forgot to revert. I will restore this in next revision based on the feedback
> on the other patch of this series. OR I can include this change in the current
> change log as a "while at it..." statement. Would you advise me?

NEVER have a "while at it..." change as part of a commit unless it is
relevant to the main change being made.  You know better...

thanks,

greg k-h

Re: [PATCH v4 2/2] tty: serial: dz: convert atomic_* to refcount_* APIs for irq_guard

Posted by Deepak R Varma 2 years, 8 months ago

On Wed, Jan 04, 2023 at 09:28:50AM +0100, Greg Kroah-Hartman wrote:
> On Tue, Jan 03, 2023 at 03:39:17PM +0530, Deepak R Varma wrote:
> > On Tue, Jan 03, 2023 at 10:00:48AM +0100, Jiri Slaby wrote:
> > > On 26. 12. 22, 7:21, Deepak R Varma wrote:
> > > > +	ret = request_irq(dport->port.irq, dz_interrupt, IRQF_SHARED, "dz", mux);
> > >
> > > How is this related to the above described change?
> >
> > No, it is not. My apologies. I must have joined the lines for improved readability
> > and forgot to revert. I will restore this in next revision based on the feedback
> > on the other patch of this series. OR I can include this change in the current
> > change log as a "while at it..." statement. Would you advise me?
>
> NEVER have a "while at it..." change as part of a commit unless it is
> relevant to the main change being made.  You know better...

Sounds very good. Thank you for the advise. I will revert the change in the next
revision.

Thank you,
./drv

>
> thanks,
>
> greg k-h