From: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Date: Thu, 19 Oct 2017 20:07:36 +0100
Subject: igb: Fix TX map failure path
Patch-mainline: v4.14-rc7
Git-commit: 104ba83363d1d42af62abb247f1426c09a80fced
References: bsc#1056651 FATE#322191 bsc#1056643 FATE#322192

When the driver cannot map a TX buffer, instead of rolling back
gracefully and retrying later, we currently get a panic:

[  159.885994] igb 0000:00:00.0: TX DMA map failed
[  159.886588] Unable to handle kernel paging request at virtual address ffff00000a08c7a8
               ...
[  159.897031] PC is at igb_xmit_frame_ring+0x9c8/0xcb8

Fix the erroneous test that leads to this situation.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/ethernet/intel/igb/igb_main.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -5326,7 +5326,7 @@ dma_error:
 				       DMA_TO_DEVICE);
 		dma_unmap_len_set(tx_buffer, len, 0);
 
-		if (i--)
+		if (i-- == 0)
 			i += tx_ring->count;
 		tx_buffer = &tx_ring->tx_buffer_info[i];
 	}