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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 <[email protected]>
Signed-off-by: Wim Van Sebroeck <[email protected]>
This commit is contained in:
Hans de Goede 2012-05-22 11:40:26 +02:00 • committed by Wim Van Sebroeck
commit f4e9c82f64
4 changed files with 29 additions and 0 deletions
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2
Documentation/watchdog/watchdog-kernel-api.txt
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@ -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