Messages in this thread Patch in this message |  | | Date | Sat, 24 Dec 2022 13:14:32 +0530 | From | Deepak R Varma <> | Subject | [PATCH v2] tty: serial: dz: convert atomic_* to refcount_* APIs |
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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.
drivers/tty/serial/dz.c | 23 +++++++++-------------- 1 file changed, 9 insertions(+), 14 deletions(-)
diff --git a/drivers/tty/serial/dz.c b/drivers/tty/serial/dz.c index 6b7ed7f2f3ca..b70edc248f8b 100644 --- a/drivers/tty/serial/dz.c +++ b/drivers/tty/serial/dz.c @@ -47,6 +47,7 @@ #include <linux/tty_flip.h>
#include <linux/atomic.h> +#include <linux/refcount.h> #include <linux/io.h> #include <asm/bootinfo.h>
@@ -75,7 +76,7 @@ struct dz_port {
struct dz_mux { struct dz_port dport[DZ_NB_PORT]; - atomic_t map_guard; + refcount_t map_guard; atomic_t irq_guard; int initialised; }; @@ -662,13 +663,11 @@ 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); }
@@ -687,23 +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) { + 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; } } 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; } -- 2.34.1
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