[PATCH v2] serial: vt8500_serial: Fix a parameter of find_first_zero_bit.

[PATCH v2] serial: vt8500_serial: Fix a parameter of find_first_zero_bit.

[Christophe JAILLET]

The 2nd parameter of 'find_first_zero_bit' is the number of bits to search.
In this case, we are passing 'sizeof(vt8500_ports_in_use)'.
'vt8500_ports_in_use' is an 'unsigned long'. So the sizeof is likely to
return 4 on a 32 bits kernel.

A few lines below, we check if it is below VT8500_MAX_PORTS, which is 6.

It is likely that the number of bits in a long was expected here.

In order to fix it:
   - use DECLARE_BITMAP when declaring the vt8500_ports_in_use
   - use VT8500_MAX_PORTS as a maximum value when checking/setting bits in
     this bitmap
   - modify code now that 'vt8500_ports_in_use' has become a pointer
     because of the use of DECLARE_BITMAP


It has been spotted by the following coccinelle script:
@@
expression ret, x;

@@
*  ret = \(find_first_bit \| find_first_zero_bit\) (x, sizeof(...));

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
v2: - use of VT8500_MAX_PORTS instead of BITS_PER_LONG to better self
      document the code
    - declare vt8500_ports_in_use with DECLARE_BITMAP in order to self
      document even better and to be foolproof should VT8500_MAX_PORTS
      be changed one day
---
 drivers/tty/serial/vt8500_serial.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/vt8500_serial.c b/drivers/tty/serial/vt8500_serial.c
index 23cfc5e16b45..6b85adce0ac9 100644
--- a/drivers/tty/serial/vt8500_serial.c
+++ b/drivers/tty/serial/vt8500_serial.c
@@ -118,7 +118,7 @@ struct vt8500_port {
  * have been allocated as we can't use pdev->id in
  * devicetree
  */
-static unsigned long vt8500_ports_in_use;
+static DECLARE_BITMAP(vt8500_ports_in_use, VT8500_MAX_PORTS);
 
 static inline void vt8500_write(struct uart_port *port, unsigned int val,
 			     unsigned int off)
@@ -663,15 +663,15 @@ static int vt8500_serial_probe(struct platform_device *pdev)
 
 	if (port < 0) {
 		/* calculate the port id */
-		port = find_first_zero_bit(&vt8500_ports_in_use,
-					sizeof(vt8500_ports_in_use));
+		port = find_first_zero_bit(vt8500_ports_in_use,
+					   VT8500_MAX_PORTS);
 	}
 
 	if (port >= VT8500_MAX_PORTS)
 		return -ENODEV;
 
 	/* reserve the port id */
-	if (test_and_set_bit(port, &vt8500_ports_in_use)) {
+	if (test_and_set_bit(port, vt8500_ports_in_use)) {
 		/* port already in use - shouldn't really happen */
 		return -EBUSY;
 	}
-- 
2.7.4


---
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Re: [PATCH v2] serial: vt8500_serial: Fix a parameter of find_first_zero_bit.

[Arnd Bergmann]

On Wednesday, August 24, 2016 7:06:58 AM CEST Christophe JAILLET wrote:
> The 2nd parameter of 'find_first_zero_bit' is the number of bits to search.
> In this case, we are passing 'sizeof(vt8500_ports_in_use)'.
> 'vt8500_ports_in_use' is an 'unsigned long'. So the sizeof is likely to
> return 4 on a 32 bits kernel.
> 
> A few lines below, we check if it is below VT8500_MAX_PORTS, which is 6.
> 
> It is likely that the number of bits in a long was expected here.
> 
> In order to fix it:
>    - use DECLARE_BITMAP when declaring the vt8500_ports_in_use
>    - use VT8500_MAX_PORTS as a maximum value when checking/setting bits in
>      this bitmap
>    - modify code now that 'vt8500_ports_in_use' has become a pointer
>      because of the use of DECLARE_BITMAP
> 
> 
> It has been spotted by the following coccinelle script:
> @@
> expression ret, x;
> 
> @@
> *  ret = \(find_first_bit \| find_first_zero_bit\) (x, sizeof(...));
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> v2: - use of VT8500_MAX_PORTS instead of BITS_PER_LONG to better self
>       document the code
>     - declare vt8500_ports_in_use with DECLARE_BITMAP in order to self
>       document even better and to be foolproof should VT8500_MAX_PORTS
>       be changed one day

Reviewed-by: Arnd Bergmann <arnd@arndb.de>