[Bug 207319] ixv driver retries xmit indefinitely

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=207319

            Bug ID: 207319
           Summary: ixv driver retries xmit indefinitely
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: Mammootty.Muthira at emc.com

I have been doing stress testing with SPECSFS on AWS with SRIOV feature with
ixv driver and getting into issues. Further debugging showed this problem in
the driver.

When mbuf chain in the ixgbe_xmit() path contains large number of segments,
mapping for dma through bus_dmamap_load_mbuf_sg() will fail with EFBIG and will
try the mapping after m_defrag(). If the total size of the data is more than
64K mapping will fail again and ixgbe_xmit() will fail. This failed packet will
be put back to the queue and the xmit failure and retry will continue
indefinitely.

Proposed fix is to drop the packet when mapping fails with EFBIG after
defragmentation.


diff --git a/sys/dev/ixgbe/ix_txrx.c b/sys/dev/ixgbe/ix_txrx.c
index 35c1ddd..d9254e2 100644
--- a/sys/dev/ixgbe/ix_txrx.c
+++ b/sys/dev/ixgbe/ix_txrx.c
@@ -389,8 +389,11 @@ retry:
                                }
                                *m_headp = m;
                                goto retry;
-                       } else
-                               return (error);
+                       }
+                       txr->no_tx_dma_setup++;
+                       m_freem(*m_headp);
+                       *m_headp = NULL;
+                       return (error);
                case ENOMEM:
                        txr->no_tx_dma_setup++;
                        return (error);

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