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watchdog: Add Locking support

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This patch fixes some potential multithreading issues, despite only
allowing one process to open the /dev/watchdog device, we can still get
called multiple times at the same time, since a program could be using thread,
or could share the fd after a fork.

This causes 2 potential problems:
1) watchdog_start / open do an unlocked test_n_set / test_n_clear,
   if these 2 race, the watchdog could be stopped while the active
   bit indicates it is running or visa versa.

2) Most watchdog_dev drivers probably assume that only one
   watchdog-op will get called at a time, this is not necessary
   true atm.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
This commit is contained in:
Hans de Goede
2012-05-22 11:40:26 +02:00
committed by Wim Van Sebroeck
parent 7a87982420
commit f4e9c82f64
4 changed files with 29 additions and 0 deletions
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5
include/linux/watchdog.h
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@@ -104,6 +104,7 @@ struct watchdog_ops {
* @min_timeout:The watchdog devices minimum timeout value.
* @max_timeout:The watchdog devices maximum timeout value.
* @driver-data:Pointer to the drivers private data.
* @lock: Lock for watchdog core internal use only.
* @status: Field that contains the devices internal status bits.
*
* The watchdog_device structure contains all information about a
@@ -111,6 +112,9 @@ struct watchdog_ops {
*
* The driver-data field may not be accessed directly. It must be accessed
* via the watchdog_set_drvdata and watchdog_get_drvdata helpers.
*
* The lock field is for watchdog core internal use only and should not be
* touched.
*/
struct watchdog_device {
int id;
@@ -124,6 +128,7 @@ struct watchdog_device {
unsigned int min_timeout;
unsigned int max_timeout;
void *driver_data;
struct mutex lock;
unsigned long status;
/* Bit numbers for status flags */
#define WDOG_ACTIVE 0 /* Is the watchdog running/active */