fcoe: convert to kworker

The driver creates its own per-CPU threads which are updated based on
CPU hotplug events. It is also possible to use kworkers and remove some
of the kthread infrastrucure.

The code checked ->thread to decide if there is an active per-CPU
thread. By using the kworker infrastructure this is no longer
possible (or required). The thread pointer is saved in `kthread' instead
of `thread' so anything trying to use thread is caught by the
compiler. Currently only the bnx2fc driver is using struct fcoe_percpu_s
and the kthread member.

After a CPU went offline, we may still enqueue items on the "offline"
CPU. This isn't much of a problem. The work will be done on a random
CPU. The allocated crc_eof_page page won't be cleaned up. It is probably
expected that the CPU comes up at some point so it should not be a
problem. The crc_eof_page memory is released of course once the module
is removed.

This patch was only compile-tested due to -ENODEV.

Cc: Vasu Dev <vasu.dev@intel.com>
Cc: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: fcoe-devel@open-fcoe.org
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/bnx2fc/bnx2fc_fcoe.c

@@ -486,7 +486,7 @@ static int bnx2fc_rcv(struct sk_buff *skb, struct net_device *dev,
 
 	__skb_queue_tail(&bg->fcoe_rx_list, skb);
 	if (bg->fcoe_rx_list.qlen == 1)
-		wake_up_process(bg->thread);
+		wake_up_process(bg->kthread);
 
 	spin_unlock(&bg->fcoe_rx_list.lock);
 
@@ -2715,7 +2715,7 @@ static int __init bnx2fc_mod_init(void)
 	}
 	wake_up_process(l2_thread);
 	spin_lock_bh(&bg->fcoe_rx_list.lock);
-	bg->thread = l2_thread;
+	bg->kthread = l2_thread;
 	spin_unlock_bh(&bg->fcoe_rx_list.lock);
 
 	for_each_possible_cpu(cpu) {
@@ -2788,8 +2788,8 @@ static void __exit bnx2fc_mod_exit(void)
 	/* Destroy global thread */
 	bg = &bnx2fc_global;
 	spin_lock_bh(&bg->fcoe_rx_list.lock);
-	l2_thread = bg->thread;
-	bg->thread = NULL;
+	l2_thread = bg->kthread;
+	bg->kthread = NULL;
 	while ((skb = __skb_dequeue(&bg->fcoe_rx_list)) != NULL)
 		kfree_skb(skb);
 

include/scsi/libfcoe.h

@@ -319,14 +319,16 @@ struct fcoe_transport {
 
 /**
  * struct fcoe_percpu_s - The context for FCoE receive thread(s)
- * @thread:	    The thread context
+ * @kthread:	    The thread context (used by bnx2fc)
+ * @work:	    The work item (used by fcoe)
  * @fcoe_rx_list:   The queue of pending packets to process
  * @page:	    The memory page for calculating frame trailer CRCs
  * @crc_eof_offset: The offset into the CRC page pointing to available
  *		    memory for a new trailer
  */
 struct fcoe_percpu_s {
-	struct task_struct *thread;
+	struct task_struct *kthread;
+	struct work_struct work;
 	struct sk_buff_head fcoe_rx_list;
 	struct page *crc_eof_page;
 	int crc_eof_offset;