staging: ozwpan: Create deferred work to destroy PD object.

Currently we call oz_pd_destroy() from softirq context, where we
try to destroy relevant data structures, as well we kill a tasklet
which always result in following kernel warning.

[12279.262194] Attempt to kill tasklet from interrupt
[12279.262202] Attempt to kill tasklet from interrupt

This patch defers deallocation of data structures to work queue.
Signed-off-by: Rupesh Gujare <rupesh.gujare@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ozwpan/ozpd.c

@@ -204,18 +204,16 @@ struct oz_pd *oz_pd_alloc(const u8 *mac_addr)
 /*------------------------------------------------------------------------------
  * Context: softirq or process
  */
-void oz_pd_destroy(struct oz_pd *pd)
+void oz_pd_free(struct work_struct *work)
 {
 	struct list_head *e;
 	struct oz_tx_frame *f;
 	struct oz_isoc_stream *st;
 	struct oz_farewell *fwell;
+	struct oz_pd *pd;
 
 	oz_pd_dbg(pd, ON, "Destroying PD\n");
-	if (hrtimer_active(&pd->timeout))
-		hrtimer_cancel(&pd->timeout);
-	if (hrtimer_active(&pd->heartbeat))
-		hrtimer_cancel(&pd->heartbeat);
+	pd = container_of(work, struct oz_pd, workitem);
 	/*Disable timer tasklets*/
 	tasklet_kill(&pd->heartbeat_tasklet);
 	tasklet_kill(&pd->timeout_tasklet);
@@ -258,6 +256,26 @@ void oz_pd_destroy(struct oz_pd *pd)
 	kfree(pd);
 }
 
+/*------------------------------------------------------------------------------
+ * Context: softirq or Process
+ */
+void oz_pd_destroy(struct oz_pd *pd)
+{
+	int ret;
+
+	if (hrtimer_active(&pd->timeout))
+		hrtimer_cancel(&pd->timeout);
+	if (hrtimer_active(&pd->heartbeat))
+		hrtimer_cancel(&pd->heartbeat);
+
+	memset(&pd->workitem, 0, sizeof(pd->workitem));
+	INIT_WORK(&pd->workitem, oz_pd_free);
+	ret = schedule_work(&pd->workitem);
+
+	if (ret)
+		oz_pd_dbg(pd, ON, "failed to schedule workitem\n");
+}
+
 /*------------------------------------------------------------------------------
  * Context: softirq-serialized
  */

drivers/staging/ozwpan/ozpd.h

@@ -99,6 +99,7 @@ struct oz_pd {
 	u8      timeout_type;
 	struct tasklet_struct   heartbeat_tasklet;
 	struct tasklet_struct   timeout_tasklet;
+	struct work_struct workitem;
 };
 
 #define OZ_MAX_QUEUED_FRAMES	4