diff --git a/mm/iob/iob_alloc_qentry.c b/mm/iob/iob_alloc_qentry.c
index e81d63327dc..b9d23db5463 100644
--- a/mm/iob/iob_alloc_qentry.c
+++ b/mm/iob/iob_alloc_qentry.c
@@ -200,7 +200,7 @@ FAR struct iob_qentry_s *iob_alloc_qentry(void)
 {
   /* Were we called from the interrupt level? */
 
-  if (up_interrupt_context())
+  if (up_interrupt_context() || sched_idletask())
     {
       /* Yes, then try to allocate an I/O buffer without waiting */
 
diff --git a/mm/iob/iob_clone.c b/mm/iob/iob_clone.c
index cfa8150f102..529de70bc6a 100644
--- a/mm/iob/iob_clone.c
+++ b/mm/iob/iob_clone.c
@@ -1,5 +1,5 @@
 /****************************************************************************
- * mm/iob/iob_copy.c
+ * mm/iob/iob_clone.c
  *
  *   Copyright (C) 2014, 2017 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
diff --git a/mm/iob/iob_concat.c b/mm/iob/iob_concat.c
index 4829c3b0724..5435fe66395 100644
--- a/mm/iob/iob_concat.c
+++ b/mm/iob/iob_concat.c
@@ -59,6 +59,11 @@
 
 void iob_concat(FAR struct iob_s *iob1, FAR struct iob_s *iob2)
 {
+  /* Combine the total packet size */
+
+  iob1->io_pktlen += iob2->io_pktlen;
+  iob2->io_pktlen  = 0;
+
   /* Find the last buffer in the iob1 buffer chain */
 
   while (iob1->io_flink)
@@ -69,8 +74,4 @@ void iob_concat(FAR struct iob_s *iob1, FAR struct iob_s *iob2)
   /* Then connect iob2 buffer chain to the end of the iob1 chain */
 
   iob1->io_flink = iob2;
-
-  /* Combine the total packet size */
-
-  iob1->io_pktlen += iob2->io_pktlen;
 }
diff --git a/mm/iob/iob_contig.c b/mm/iob/iob_contig.c
index ee71ec05fc4..2e77127ed5e 100644
--- a/mm/iob/iob_contig.c
+++ b/mm/iob/iob_contig.c
@@ -113,7 +113,7 @@ int iob_contig(FAR struct iob_s *iob, unsigned int len)
           /* Get the next I/O buffer in the chain */
 
           next = iob->io_flink;
-          DEBUGASSERT(next != NULL && next->io_len > 0);
+          DEBUGASSERT(next != NULL);
 
           /* Copy what we need or what we can from the next buffer */
 
diff --git a/mm/iob/iob_free.c b/mm/iob/iob_free.c
index c92a7465685..57d858ac856 100644
--- a/mm/iob/iob_free.c
+++ b/mm/iob/iob_free.c
@@ -115,12 +115,11 @@ FAR struct iob_s *iob_free(FAR struct iob_s *iob)
         }
       else
         {
-          /* This can only happen if the next entry is last entry in the
-           * chain... and if it is empty
+          /* This can only happen if the free entry isn't first entry in the
+           * chain...
            */
 
           next->io_pktlen = 0;
-          DEBUGASSERT(next->io_len == 0 && next->io_flink == NULL);
         }
 
       iobinfo("next=%p io_pktlen=%u io_len=%u\n",
diff --git a/mm/iob/iob_free_qentry.c b/mm/iob/iob_free_qentry.c
index 559753ea984..e08daeeb943 100644
--- a/mm/iob/iob_free_qentry.c
+++ b/mm/iob/iob_free_qentry.c
@@ -76,13 +76,13 @@ FAR struct iob_qentry_s *iob_free_qentry(FAR struct iob_qentry_s *iobq)
 
   flags = enter_critical_section();
 
-  /* Which list?  If there is a task waiting for an IOB, then put
-   * the IOB on either the free list or on the committed list where
+  /* Which list?  If there is a task waiting for an IOB chain, then put
+   * the IOB chain on either the free list or on the committed list where
    * it is reserved for that allocation (and not available to
-   * iob_tryalloc()).
+   * iob_tryalloc_qentry()).
    */
 
-  if (g_iob_sem.semcount < 0)
+  if (g_qentry_sem.semcount < 0)
     {
       iobq->qe_flink   = g_iob_qcommitted;
       g_iob_qcommitted = iobq;
diff --git a/mm/iob/iob_navail.c b/mm/iob/iob_navail.c
index 2c3b157083f..75926131342 100644
--- a/mm/iob/iob_navail.c
+++ b/mm/iob/iob_navail.c
@@ -77,12 +77,12 @@ int iob_navail(bool throttled)
       if (throttled)
         {
           ret -= CONFIG_IOB_THROTTLE;
-          if (ret < 0)
-            {
-              ret = 0;
-            }
         }
 #endif
+      if (ret < 0)
+        {
+          ret = 0;
+        }
     }
 
 #else
@@ -112,6 +112,10 @@ int iob_qentry_navail(void)
   if (ret >= 0)
     {
       ret = navail;
+      if (ret < 0)
+        {
+          ret = 0;
+        }
     }
 
 #else
diff --git a/mm/iob/iob_pack.c b/mm/iob/iob_pack.c
index 62799b2238b..011652c99d5 100644
--- a/mm/iob/iob_pack.c
+++ b/mm/iob/iob_pack.c
@@ -45,14 +45,6 @@
 
 #include "iob.h"
 
-/****************************************************************************
- * Pre-processor Definitions
- ****************************************************************************/
-
-#ifndef MIN
-#  define MIN(a,b) ((a) < (b) ? (a) : (b))
-#endif
-
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -79,6 +71,10 @@ FAR struct iob_s *iob_pack(FAR struct iob_s *iob)
   while (iob->io_len <= 0)
     {
       iob = iob_free(iob);
+      if (iob == NULL)
+        {
+          return NULL;
+        }
     }
 
   /* Now remember the head of the chain (for the return value) */