[SCSI] fcoe: fix handling of pending queue, prevent out of order frames (v3)

In fcoe_check_wait_queue() the queue length could temporarily drop to 0,
before the last frame was successfully sent.  This resulted in out of order
data frames within a single sequence, leading to IO timeout errors.

This builds on the approach from Vasu Dev to only fix the queue management in
fcoe_check_wait_queue, where my first patch added locking to the transmit
path even when the pending queue was not in use.

This patch continues to use fcoe_pending_queue.qlen instead of introducing a
new length counter, but takes precautions to ensure it never drops to 0 before
the final frame in the queue has successfully been passed to the netdev qdisc
layer.  It also includes some cleanup of fcoe_check_wait_queue and removes the
fcoe_insert_wait_queue(_head) wrapper functions.

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 24 insertions, 57 deletions

diff --git a/drivers/scsi/fcoe/libfcoe.c b/drivers/scsi/fcoe/libfcoe.c
index 14dd8a0402b6..0e0b494fc17c 100644
--- a/drivers/scsi/fcoe/libfcoe.c
+++ b/drivers/scsi/fcoe/libfcoe.c
@@ -70,8 +70,6 @@ struct fcoe_percpu_s *fcoe_percpu[NR_CPUS];
 
 /* Function Prototyes */
 static int fcoe_check_wait_queue(struct fc_lport *);
-static void fcoe_insert_wait_queue_head(struct fc_lport *, struct sk_buff *);
-static void fcoe_insert_wait_queue(struct fc_lport *, struct sk_buff *);
 static void fcoe_recv_flogi(struct fcoe_softc *, struct fc_frame *, u8 *);
 #ifdef CONFIG_HOTPLUG_CPU
 static int fcoe_cpu_callback(struct notifier_block *, ulong, void *);
@@ -501,7 +499,9 @@ int fcoe_xmit(struct fc_lport *lp, struct fc_frame *fp)
                 rc = fcoe_start_io(skb);
 
         if (rc) {
-                fcoe_insert_wait_queue(lp, skb);
+                spin_lock_bh(&fc->fcoe_pending_queue.lock);
+                __skb_queue_tail(&fc->fcoe_pending_queue, skb);
+                spin_unlock_bh(&fc->fcoe_pending_queue.lock);
                 if (fc->fcoe_pending_queue.qlen > FCOE_MAX_QUEUE_DEPTH)
                         lp->qfull = 1;
         }
@@ -756,33 +756,36 @@ void fcoe_watchdog(ulong vp)
  */
 static int fcoe_check_wait_queue(struct fc_lport *lp)
 {
+        struct fcoe_softc *fc = lport_priv(lp);
         struct sk_buff *skb;
-        struct fcoe_softc *fc;
         int rc = -1;
 
-        fc = lport_priv(lp);
         spin_lock_bh(&fc->fcoe_pending_queue.lock);
-
         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)
-                                fcoe_insert_wait_queue_head(lp, skb);
-                        spin_lock_bh(&fc->fcoe_pending_queue.lock);
-                        if (rc)
-                                break;
+
+        while (fc->fcoe_pending_queue.qlen) {
+                /* keep qlen > 0 until fcoe_start_io succeeds */
+                fc->fcoe_pending_queue.qlen++;
+                skb = __skb_dequeue(&fc->fcoe_pending_queue);
+
+                spin_unlock_bh(&fc->fcoe_pending_queue.lock);
+                rc = fcoe_start_io(skb);
+                spin_lock_bh(&fc->fcoe_pending_queue.lock);
+
+                if (rc) {
+                        __skb_queue_head(&fc->fcoe_pending_queue, skb);
+                        /* undo temporary increment above */
+                        fc->fcoe_pending_queue.qlen--;
+                        break;
                 }
-                /*
-                 * 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;
+                /* undo temporary increment above */
+                fc->fcoe_pending_queue.qlen--;
         }
+
+        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:
@@ -791,42 +794,6 @@ out:
 }
 
 /**
- * fcoe_insert_wait_queue_head() - puts skb to fcoe pending queue head
- * @lp: the fc_port for this skb
- * @skb: the associated skb to be xmitted
- *
- * Returns: none
- */
-static void fcoe_insert_wait_queue_head(struct fc_lport *lp,
-                                        struct sk_buff *skb)
-{
-        struct fcoe_softc *fc;
-
-        fc = lport_priv(lp);
-        spin_lock_bh(&fc->fcoe_pending_queue.lock);
-        __skb_queue_head(&fc->fcoe_pending_queue, skb);
-        spin_unlock_bh(&fc->fcoe_pending_queue.lock);
-}
-
-/**
- * fcoe_insert_wait_queue() - put the skb into fcoe pending queue tail
- * @lp: the fc_port for this skb
- * @skb: the associated skb to be xmitted
- *
- * Returns: none
- */
-static void fcoe_insert_wait_queue(struct fc_lport *lp,
-                                   struct sk_buff *skb)
-{
-        struct fcoe_softc *fc;
-
-        fc = lport_priv(lp);
-        spin_lock_bh(&fc->fcoe_pending_queue.lock);
-        __skb_queue_tail(&fc->fcoe_pending_queue, skb);
-        spin_unlock_bh(&fc->fcoe_pending_queue.lock);
-}
-
-/**
  * fcoe_dev_setup() - setup link change notification interface
  */
 static void fcoe_dev_setup()