Re: LinuxPPS & spinlocks

Rodolfo Giometti
2007-07-29T09:58:35Z

On Sat, Jul 28, 2007 at 05:11:17AM +0530, Satyam Sharma wrote:

> Take the race between the time_pps_setparams() syscall and a concurrent
> pps_event() from an interrupt for instance. From sys_time_pps_setparams,
> the parameters for an existing source are not modified / set atomically,
> which means a pps_event() called on the same source in between will see
> invalid parameters ... and bad things will happen.

I think this should be a good solution... :)

diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
index 08de71d..f0c42ec 100644
--- a/drivers/pps/kapi.c
+++ b/drivers/pps/kapi.c
@@ -29,12 +29,6 @@
#include <linux/pps.h>

/*
- * Local variables
- */
-
-static spinlock_t pps_lock = SPIN_LOCK_UNLOCKED;
-
-/*
* Local functions
*/

diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 9176c01..91b7e4d 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -35,6 +35,7 @@

struct pps_s pps_source[PPS_MAX_SOURCES];
DEFINE_MUTEX(pps_mutex);
+spinlock_t pps_lock = SPIN_LOCK_UNLOCKED;

/*
* Misc functions
@@ -227,6 +228,8 @@ asmlinkage long sys_time_pps_setparams(int source,
goto sys_time_pps_setparams_exit;
}

+ spin_lock(&pps_lock);
+
/* Save the new parameters */
ret = copy_from_user(&pps_source[source].params, params,
sizeof(struct pps_kparams));
@@ -245,6 +248,8 @@ asmlinkage long sys_time_pps_setparams(int source,
pps_source[source].params.mode |= PPS_CANWAIT;
pps_source[source].params.api_version = PPS_API_VERS;

+ spin_unlock(&pps_lock);
+
sys_time_pps_setparams_exit:
mutex_unlock(&pps_mutex);

diff --git a/include/linux/pps.h b/include/linux/pps.h
index 6eca3ea..93e7384 100644
--- a/include/linux/pps.h
+++ b/include/linux/pps.h
@@ -174,6 +174,7 @@ struct pps_s {

extern struct pps_s pps_source[PPS_MAX_SOURCES];
extern struct mutex pps_mutex;
+extern spinlock_t pps_lock;

/*
* Global functions

Ciao,

Rodolfo

--

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