[PATCH 4.4 58/96] ixgbe: Fix skb list corruption on Power systems

Greg Kroah-Hartman
2017-11-28T10:30:47Z

From: Brian King <brking@linux.vnet.ibm.com>

commit 0a9a17e3bb4564caf4bfe2a6783ae1287667d188 upstream.

This patch fixes an issue seen on Power systems with ixgbe which results
in skb list corruption and an eventual kernel oops. The following is what
was observed:

CPU 1 CPU2
============================ ============================
1: ixgbe_xmit_frame_ring ixgbe_clean_tx_irq
2: first->skb = skb eop_desc = tx_buffer->next_to_watch
3: ixgbe_tx_map read_barrier_depends()
4: wmb check adapter written status bit
5: first->next_to_watch = tx_desc napi_consume_skb(tx_buffer->skb ..);
6: writel(i, tx_ring->tail);

The read_barrier_depends is insufficient to ensure that tx_buffer->skb does not
get loaded prior to tx_buffer->next_to_watch, which then results in loading
a stale skb pointer. This patch replaces the read_barrier_depends with
smp_rmb to ensure loads are ordered with respect to the load of
tx_buffer->next_to_watch.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Acked-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1114,7 +1114,7 @@ static bool ixgbe_clean_tx_irq(struct ix
break;

/* prevent any other reads prior to eop_desc */
- read_barrier_depends();
+ smp_rmb();

/* if DD is not set pending work has not been completed */
if (!(eop_desc->wb.status & cpu_to_le32(IXGBE_TXD_STAT_DD)))