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Subject[PATCH 10/17] gpiolib: cdev: fix minor race in GET_LINEINFO_WATCH
Date
Merge separate usage of test_bit/set_bit into test_and_set_bit to remove
the possibility of a race between the test and set.

Similarly test_bit and clear_bit.

In the existing code it is possible for two threads to race past the
test_bit and then set or clear the watch bit, and neither return EBUSY.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
---
drivers/gpio/gpiolib-cdev.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index fe1b385deecc..b2b26dc25051 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -887,15 +887,16 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

hwgpio = gpio_chip_hwgpio(desc);

- if (test_bit(hwgpio, cdev->watched_lines))
+ if (test_and_set_bit(hwgpio, cdev->watched_lines))
return -EBUSY;

gpio_desc_to_lineinfo(desc, &lineinfo);

- if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
+ if (copy_to_user(ip, &lineinfo, sizeof(lineinfo))) {
+ clear_bit(hwgpio, cdev->watched_lines);
return -EFAULT;
+ }

- set_bit(hwgpio, cdev->watched_lines);
return 0;
} else if (cmd == GPIO_GET_LINEINFO_UNWATCH_IOCTL) {
if (copy_from_user(&offset, ip, sizeof(offset)))
@@ -907,10 +908,9 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

hwgpio = gpio_chip_hwgpio(desc);

- if (!test_bit(hwgpio, cdev->watched_lines))
+ if (!test_and_clear_bit(hwgpio, cdev->watched_lines))
return -EBUSY;

- clear_bit(hwgpio, cdev->watched_lines);
return 0;
}
return -EINVAL;
--
2.27.0
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