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Subject[PATCH v2] tty: serial: dz: convert atomic_* to refcount_* APIs for irq_guard
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>
---

Changes in v2:
1. Separate the combined change into one variable per patch as
suggested by gregkh@linuxfoundation.org
2. There was additional feedback on validating the change as it appeared to
modify the existing logic. However, I found that the logic does not
change with the proposed refcount_* APIs used in this change. Hence that
feedback is not applied in this version.

Please Note:
The patch is compile tested using dec_station.defconfig for MIPS architecture.


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


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