[PATCH v3] staging: dgnc: take lock when storing value in dgnc_poll_tick

[PATCH v3] staging: dgnc: take lock when storing value in dgnc_poll_tick

[Salah Triki]

poll_tick is declared global, so dgnc_driver_pollrate_store needs to take
the lock dgnc_poll_lock before modifying this variable. dgnc_poll_lock the
appropriate lock, since it is intended for poll scheduling and dgnc_poll_tick
contains the poll rate. dgnc_poll_lock needs to be declared not static and
extern in order to be visible for dgnc_driver_pollrate_store.

Signed-off-by: Salah Triki <salah.triki@acm.org>
---
 drivers/staging/dgnc/dgnc_driver.c | 2 +-
 drivers/staging/dgnc/dgnc_driver.h | 1 +
 drivers/staging/dgnc/dgnc_sysfs.c  | 9 ++++++++-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/dgnc/dgnc_driver.c b/drivers/staging/dgnc/dgnc_driver.c
index 7546aff..f03e8b3 100644
--- a/drivers/staging/dgnc/dgnc_driver.c
+++ b/drivers/staging/dgnc/dgnc_driver.c
@@ -64,6 +64,7 @@ static const struct file_operations dgnc_BoardFops = {
 uint			dgnc_NumBoards;
 struct dgnc_board		*dgnc_Board[MAXBOARDS];
 DEFINE_SPINLOCK(dgnc_global_lock);
+DEFINE_SPINLOCK(dgnc_poll_lock);
 uint			dgnc_Major;
 int			dgnc_poll_tick = 20;	/* Poll interval - 20 ms */
 
@@ -75,7 +76,6 @@ static struct class *dgnc_class;
 /*
  * Poller stuff
  */
-static DEFINE_SPINLOCK(dgnc_poll_lock); /* Poll scheduling lock */
 static ulong		dgnc_poll_time; /* Time of next poll */
 static uint		dgnc_poll_stop; /* Used to tell poller to stop */
 static struct timer_list dgnc_poll_timer;
diff --git a/drivers/staging/dgnc/dgnc_driver.h b/drivers/staging/dgnc/dgnc_driver.h
index 06ece51..6784d81 100644
--- a/drivers/staging/dgnc/dgnc_driver.h
+++ b/drivers/staging/dgnc/dgnc_driver.h
@@ -389,6 +389,7 @@ struct channel_t {
  */
 extern uint		dgnc_Major;		/* Our driver/mgmt major */
 extern int		dgnc_poll_tick;		/* Poll interval - 20 ms */
+extern spinlock_t	dgnc_poll_lock;		/* Poll scheduling lock */
 extern spinlock_t	dgnc_global_lock;	/* Driver global spinlock */
 extern uint		dgnc_NumBoards;		/* Total number of boards */
 extern struct dgnc_board	*dgnc_Board[MAXBOARDS];	/* Array of board structs */
diff --git a/drivers/staging/dgnc/dgnc_sysfs.c b/drivers/staging/dgnc/dgnc_sysfs.c
index 44db870..48b6056 100644
--- a/drivers/staging/dgnc/dgnc_sysfs.c
+++ b/drivers/staging/dgnc/dgnc_sysfs.c
@@ -56,11 +56,18 @@ static ssize_t dgnc_driver_pollrate_show(struct device_driver *ddp, char *buf)
 static ssize_t dgnc_driver_pollrate_store(struct device_driver *ddp,
 					  const char *buf, size_t count)
 {
+	unsigned long flags;
+	int tick;
 	int ret;
 
-	ret = sscanf(buf, "%d\n", &dgnc_poll_tick);
+	ret = sscanf(buf, "%d\n", &tick);
 	if (ret != 1)
 		return -EINVAL;
+
+	spin_lock_irqsave(&dgnc_poll_lock, flags);
+	dgnc_poll_tick = tick;
+	spin_unlock_irqrestore(&dgnc_poll_lock, flags);
+
 	return count;
 }
 static DRIVER_ATTR(pollrate, (S_IRUSR | S_IWUSR), dgnc_driver_pollrate_show,
-- 
1.9.1

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Re: [PATCH v3] staging: dgnc: take lock when storing value in dgnc_poll_tick

[Greg KH]

On Tue, Aug 25, 2015 at 08:09:47PM +0100, Salah Triki wrote:
> poll_tick is declared global, so dgnc_driver_pollrate_store needs to take
> the lock dgnc_poll_lock before modifying this variable. dgnc_poll_lock the
> appropriate lock, since it is intended for poll scheduling and dgnc_poll_tick
> contains the poll rate. dgnc_poll_lock needs to be declared not static and
> extern in order to be visible for dgnc_driver_pollrate_store.

So you only lock it if you change the value?  That's not the way to do
this type of change :(

Re: [PATCH v3] staging: dgnc: take lock when storing value in dgnc_poll_tick

[Greg KH]

On Tue, Sep 22, 2015 at 11:48:05AM +0100, Salah Triki wrote:
> >On Wed, 2 Sep 2015 18:15:29 -0700, Greg KH wrote:
> >>On Tue, Aug 25, 2015 at 08:09:47PM +0100, Salah Triki wrote:
> >> poll_tick is declared global, so dgnc_driver_pollrate_store needs to
> >> take
> >> the lock dgnc_poll_lock before modifying this variable. dgnc_poll_lock
> >> the
> >> appropriate lock, since it is intended for poll scheduling and
> >> dgnc_poll_tick
> >> contains the poll rate. dgnc_poll_lock needs to be declared not static
> >> and
> >> extern in order to be visible for dgnc_driver_pollrate_store.
> >
> >So you only lock it if you change the value?  That's not the way to do
> >this type of change :(
> 
> The reads access to dgnc_poll_tick are protected.

protected with what?  I don't see the patch here and do not even
remember what it contained to be able to answer this, sorry.

Please resend if you think it is correct.

greg k-h

Re: [PATCH v3] staging: dgnc: take lock when storing value in dgnc_poll_tick

[Salah Triki]

>On Wed, 2 Sep 2015 18:15:29 -0700, Greg KH wrote:
>>On Tue, Aug 25, 2015 at 08:09:47PM +0100, Salah Triki wrote:
>> poll_tick is declared global, so dgnc_driver_pollrate_store needs to
>> take
>> the lock dgnc_poll_lock before modifying this variable. dgnc_poll_lock
>> the
>> appropriate lock, since it is intended for poll scheduling and
>> dgnc_poll_tick
>> contains the poll rate. dgnc_poll_lock needs to be declared not static
>> and
>> extern in order to be visible for dgnc_driver_pollrate_store.
>
>So you only lock it if you change the value?  That's not the way to do
>this type of change :(

The reads access to dgnc_poll_tick are protected.

regards,
salah triki
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