[SCSI] fcoe: Out of order tx frames was causing several check condition SCSI status

frames followed by these errors in log.

	[sdp] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE,SUGGEST_OK
	[sdp] Sense Key : Aborted Command [current]
	[sdp] Add. Sense: Data phase error

This was causing some test apps to exit due to write failure under heavy
load.

This was due to a race around adding and removing tx frame skb in
fcoe_pending_queue, Chris Leech helped me to find that brief unlocking
period when pulling skb from fcoe_pending_queue in various contexts
(fcoe_watchdog and fcoe_xmit) and then adding skb back into fcoe_pending_queue
up on a failed fcoe_start_io could change skb/tx frame order in
fcoe_pending_queue. Thanks Chris.

This patch allows only single context to pull skb from fcoe_pending_queue
at any time to prevent above described ordering issue/race by use of
fcoe_pending_queue_active flag.

This patch simplified fcoe_watchdog with modified fcoe_check_wait_queue by
use of FCOE_LOW_QUEUE_DEPTH instead previously used several conditionals
to clear and set lp->qfull.

I think FCOE_MAX_QUEUE_DEPTH with FCOE_LOW_QUEUE_DEPTH  will work better
in re/setting lp->qfull and these could be fine tuned for performance.

Signed-off-by: Vasu Dev <vasu.dev@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

2 files changed, 22 insertions, 24 deletions

diff --git a/drivers/scsi/fcoe/fcoe_sw.c b/drivers/scsi/fcoe/fcoe_sw.c
index 37d359db164..da210eba194 100644
--- a/drivers/scsi/fcoe/fcoe_sw.c
+++ b/drivers/scsi/fcoe/fcoe_sw.c
@@ -188,6 +188,7 @@ static int fcoe_sw_netdev_config(struct fc_lport *lp, struct net_device *netdev)
 
 
         skb_queue_head_init(&fc->fcoe_pending_queue);
+        fc->fcoe_pending_queue_active = 0;
 
         /* setup Source Mac Address */
         memcpy(fc->ctl_src_addr, fc->real_dev->dev_addr,
diff --git a/drivers/scsi/fcoe/libfcoe.c b/drivers/scsi/fcoe/libfcoe.c
index 7265e093799..14dd8a0402b 100644
--- a/drivers/scsi/fcoe/libfcoe.c
+++ b/drivers/scsi/fcoe/libfcoe.c
@@ -49,6 +49,7 @@
 static int debug_fcoe;
 
 #define FCOE_MAX_QUEUE_DEPTH  256
+#define FCOE_LOW_QUEUE_DEPTH  32
 
 /* destination address mode */
 #define FCOE_GW_ADDR_MODE           0x00
@@ -723,21 +724,12 @@ static void fcoe_recv_flogi(struct fcoe_softc *fc, struct fc_frame *fp, u8 *sa)
  */
 void fcoe_watchdog(ulong vp)
 {
-        struct fc_lport *lp;
         struct fcoe_softc *fc;
-        int qfilled = 0;
 
         read_lock(&fcoe_hostlist_lock);
         list_for_each_entry(fc, &fcoe_hostlist, list) {
-                lp = fc->lp;
-                if (lp) {
-                        if (fc->fcoe_pending_queue.qlen > FCOE_MAX_QUEUE_DEPTH)
-                                qfilled = 1;
-                        if (fcoe_check_wait_queue(lp) <  FCOE_MAX_QUEUE_DEPTH) {
-                                if (qfilled)
-                                        lp->qfull = 0;
-                        }
-                }
+                if (fc->lp)
+                        fcoe_check_wait_queue(fc->lp);
         }
         read_unlock(&fcoe_hostlist_lock);
 
@@ -753,8 +745,8 @@ void fcoe_watchdog(ulong vp)
  *
  * This empties the wait_queue, dequeue the head of the wait_queue queue
  * and calls fcoe_start_io() for each packet, if all skb have been
- * transmitted, return 0 if a error occurs, then restore wait_queue and
- * try again later.
+ * transmitted, return qlen or -1 if a error occurs, then restore
+ * wait_queue and  try again later.
  *
  * The wait_queue is used when the skb transmit fails. skb will go
  * in the wait_queue which will be emptied by the time function OR
@@ -764,33 +756,38 @@ void fcoe_watchdog(ulong vp)
  */
 static int fcoe_check_wait_queue(struct fc_lport *lp)
 {
-        int rc;
         struct sk_buff *skb;
         struct fcoe_softc *fc;
+        int rc = -1;
 
         fc = lport_priv(lp);
         spin_lock_bh(&fc->fcoe_pending_queue.lock);
 
-        /*
-         * if interface pending queue full then set qfull in lport.
-         */
-        if (fc->fcoe_pending_queue.qlen > FCOE_MAX_QUEUE_DEPTH)
-                lp->qfull = 1;
+        if (fc->fcoe_pending_queue_active)
+                goto out;
+        fc->fcoe_pending_queue_active = 1;
         if (fc->fcoe_pending_queue.qlen) {
                 while ((skb = __skb_dequeue(&fc->fcoe_pending_queue)) != NULL) {
                         spin_unlock_bh(&fc->fcoe_pending_queue.lock);
                         rc = fcoe_start_io(skb);
-                        if (rc) {
+                        if (rc)
                                 fcoe_insert_wait_queue_head(lp, skb);
-                                return rc;
-                        }
                         spin_lock_bh(&fc->fcoe_pending_queue.lock);
+                        if (rc)
+                                break;
                 }
-                if (fc->fcoe_pending_queue.qlen < FCOE_MAX_QUEUE_DEPTH)
+                /*
+                 * if interface pending queue is below FCOE_LOW_QUEUE_DEPTH
+                 * then clear qfull flag.
+                 */
+                if (fc->fcoe_pending_queue.qlen < FCOE_LOW_QUEUE_DEPTH)
                         lp->qfull = 0;
         }
+        fc->fcoe_pending_queue_active = 0;
+        rc = fc->fcoe_pending_queue.qlen;
+out:
         spin_unlock_bh(&fc->fcoe_pending_queue.lock);
-        return fc->fcoe_pending_queue.qlen;
+        return rc;
 }
 
 /**