watchdog: Add Locking support

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>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
index ce1fa22aa70b..08d34e11bc54 100644
--- a/Documentation/watchdog/watchdog-kernel-api.txt
+++ b/Documentation/watchdog/watchdog-kernel-api.txt
@@ -50,6 +50,7 @@ struct watchdog_device {
         unsigned int min_timeout;
         unsigned int max_timeout;
         void *driver_data;
+        struct mutex lock;
         unsigned long status;
 };
 
@@ -74,6 +75,7 @@ It contains following fields:
 * driver_data: a pointer to the drivers private data of a watchdog device.
   This data should only be accessed via the watchdog_set_drvdata and
   watchdog_get_drvdata routines.
+* lock: Mutex for WatchDog Timer Driver Core internal use only.
 * status: this field contains a number of status bits that give extra
   information about the status of the device (Like: is the watchdog timer
   running/active, is the nowayout bit set, is the device opened via