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Date:   Thu, 22 Dec 2022 01:27:40 +0530
From:   Deepak R Varma <drv@mailo.com>
To:     "Maciej W. Rozycki" <macro@orcam.me.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Saurabh Singh Sengar <ssengar@microsoft.com>,
        Praveen Kumar <kumarpraveen@linux.microsoft.com>, drv@mailo.com
Subject: [PATCH] tty: serial: convert atomic_* to refcount_* APIs
Message-ID: <Y6NlNB9c22XiYHdD@qemulion>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Precedence: bulk

The refcount_* APIs are designed to address known issues with the
atomic_t APIs for reference counting. They protect the reference
counters from overflow/underflow, use-after-free errors, provide
improved memory ordering guarantee schemes, are 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>
---
Note: The patch is compile tested using dec_station.defconfig for
      MIPS architecture.


 drivers/tty/serial/dz.c | 34 +++++++++++++---------------------
 drivers/tty/serial/zs.c | 11 ++++-------
 drivers/tty/serial/zs.h |  2 +-
 3 files changed, 18 insertions(+), 29 deletions(-)

diff --git a/drivers/tty/serial/dz.c b/drivers/tty/serial/dz.c
index 6b7ed7f2f3ca..c248201f9499 100644
--- a/drivers/tty/serial/dz.c
+++ b/drivers/tty/serial/dz.c
@@ -46,7 +46,7 @@
 #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>

@@ -75,8 +75,8 @@ struct dz_port {

 struct dz_mux {
 	struct dz_port		dport[DZ_NB_PORT];
-	atomic_t		map_guard;
-	atomic_t		irq_guard;
+	refcount_t		map_guard;
+	refcount_t		irq_guard;
 	int			initialised;
 };

@@ -399,18 +399,17 @@ 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);
 	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;
 	}
@@ -440,15 +439,13 @@ 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);
@@ -662,13 +659,11 @@ static const char *dz_type(struct uart_port *uport)
 static void dz_release_port(struct uart_port *uport)
 {
 	struct dz_mux *mux = to_dport(uport)->mux;
-	int map_guard;

 	iounmap(uport->membase);
 	uport->membase = NULL;

-	map_guard = atomic_add_return(-1, &mux->map_guard);
-	if (!map_guard)
+	if (refcount_dec_and_test(&mux->map_guard))
 		release_mem_region(uport->mapbase, dec_kn_slot_size);
 }

@@ -687,14 +682,12 @@ 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);
+	refcount_inc(&mux->map_guard);
+	if (refcount_read(&mux->map_guard) == 1) {
+		if (!request_mem_region(uport->mapbase, dec_kn_slot_size, "dz")) {
+			refcount_dec(&mux->map_guard);
 			printk(KERN_ERR
 			       "dz: Unable to reserve MMIO resource\n");
 			return -EBUSY;
@@ -702,8 +695,7 @@ static int dz_request_port(struct uart_port *uport)
 	}
 	ret = dz_map_port(uport);
 	if (ret) {
-		map_guard = atomic_add_return(-1, &mux->map_guard);
-		if (!map_guard)
+		if (refcount_dec_and_test(&mux->map_guard))
 			release_mem_region(uport->mapbase, dec_kn_slot_size);
 		return ret;
 	}
diff --git a/drivers/tty/serial/zs.c b/drivers/tty/serial/zs.c
index 730c648e32ff..6fa79705a0c9 100644
--- a/drivers/tty/serial/zs.c
+++ b/drivers/tty/serial/zs.c
@@ -753,15 +753,14 @@ static int zs_startup(struct uart_port *uport)
 	struct zs_port *zport = to_zport(uport);
 	struct zs_scc *scc = zport->scc;
 	unsigned long flags;
-	int irq_guard;
 	int ret;

-	irq_guard = atomic_add_return(1, &scc->irq_guard);
-	if (irq_guard == 1) {
+	refcount_inc(&scc->irq_guard);
+	if (refcount_read(&scc->irq_guard) == 1) {
 		ret = request_irq(zport->port.irq, zs_interrupt,
 				  IRQF_SHARED, "scc", scc);
 		if (ret) {
-			atomic_add(-1, &scc->irq_guard);
+			refcount_dec(&scc->irq_guard);
 			printk(KERN_ERR "zs: can't get irq %d\n",
 			       zport->port.irq);
 			return ret;
@@ -806,7 +805,6 @@ static void zs_shutdown(struct uart_port *uport)
 	struct zs_port *zport = to_zport(uport);
 	struct zs_scc *scc = zport->scc;
 	unsigned long flags;
-	int irq_guard;

 	spin_lock_irqsave(&scc->zlock, flags);

@@ -816,8 +814,7 @@ static void zs_shutdown(struct uart_port *uport)

 	spin_unlock_irqrestore(&scc->zlock, flags);

-	irq_guard = atomic_add_return(-1, &scc->irq_guard);
-	if (!irq_guard)
+	if (refcount_dec_and_test(&scc->irq_guard))
 		free_irq(zport->port.irq, scc);
 }

diff --git a/drivers/tty/serial/zs.h b/drivers/tty/serial/zs.h
index 26ef8eafa1c1..bd97b73d7e16 100644
--- a/drivers/tty/serial/zs.h
+++ b/drivers/tty/serial/zs.h
@@ -40,7 +40,7 @@ struct zs_port {
 struct zs_scc {
 	struct zs_port	zport[2];
 	spinlock_t	zlock;
-	atomic_t	irq_guard;
+	refcount_t	irq_guard;
 	int		initialised;
 };

--
2.34.1