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Subject[PATCH] staging: panel: Fix single-open policy race condition
Date
Fix the implementation of a single-open policy for both
devices (lcd and keypad) by using atomic_t instead of plain ints.

Signed-off-by: Mariusz Gorski <marius.gorski@gmail.com>
---
drivers/staging/panel/panel.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/panel/panel.c b/drivers/staging/panel/panel.c
index 98556ce..d30ccb5 100644
--- a/drivers/staging/panel/panel.c
+++ b/drivers/staging/panel/panel.c
@@ -404,8 +404,11 @@ static unsigned char lcd_bits[LCD_PORTS][LCD_BITS][BIT_STATES];
#endif /* DEFAULT_PROFILE == 0 */

/* global variables */
-static int keypad_open_cnt; /* #times opened */
-static int lcd_open_cnt; /* #times opened */
+
+/* Device single-open policy control */
+static atomic_t lcd_available = ATOMIC_INIT(1);
+static atomic_t keypad_available = ATOMIC_INIT(1);
+
static struct pardevice *pprt;

static int lcd_initialized;
@@ -1347,7 +1350,7 @@ static ssize_t lcd_write(struct file *file,

static int lcd_open(struct inode *inode, struct file *file)
{
- if (lcd_open_cnt)
+ if (!atomic_dec_and_test(&lcd_available))
return -EBUSY; /* open only once at a time */

if (file->f_mode & FMODE_READ) /* device is write-only */
@@ -1357,13 +1360,12 @@ static int lcd_open(struct inode *inode, struct file *file)
lcd_clear_display();
lcd_must_clear = 0;
}
- lcd_open_cnt++;
return nonseekable_open(inode, file);
}

static int lcd_release(struct inode *inode, struct file *file)
{
- lcd_open_cnt--;
+ atomic_inc(&lcd_available);
return 0;
}

@@ -1627,20 +1629,19 @@ static ssize_t keypad_read(struct file *file,

static int keypad_open(struct inode *inode, struct file *file)
{
- if (keypad_open_cnt)
+ if (!atomic_dec_and_test(&keypad_available))
return -EBUSY; /* open only once at a time */

if (file->f_mode & FMODE_WRITE) /* device is read-only */
return -EPERM;

keypad_buflen = 0; /* flush the buffer on opening */
- keypad_open_cnt++;
return 0;
}

static int keypad_release(struct inode *inode, struct file *file)
{
- keypad_open_cnt--;
+ atomic_inc(&keypad_available);
return 0;
}

@@ -1663,7 +1664,7 @@ static void keypad_send_key(const char *string, int max_len)
return;

/* send the key to the device only if a process is attached to it. */
- if (keypad_open_cnt > 0) {
+ if (!atomic_read(&keypad_available)) {
while (max_len-- && keypad_buflen < KEYPAD_BUFFER && *string) {
keypad_buffer[(keypad_start + keypad_buflen++) %
KEYPAD_BUFFER] = *string++;
--
2.1.3


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