Starting with commit a3bc1f11e9b867a4f49505 ("gianfar: Revive SKB
recycling") gianfar driver sooner or later stops transmitting any
packets on SMP machines.
start_xmit() prepares new skb for transmitting, generally it does
three things:
1. sets up all BDs (marks them ready to send), except the first one.
2. stores skb into tx_queue->tx_skbuff so that clean_tx_ring()
would cleanup it later.
3. sets up the first BD, i.e. marks it ready.
Here is what clean_tx_ring() does:
1. reads skbs from tx_queue->tx_skbuff
2. checks if the *last* BD is ready. If it's still ready [to send]
then it it isn't transmitted, so clean_tx_ring() returns.
Otherwise it actually cleanups BDs. All is OK.
Now, if there is just one BD, code flow:
- start_xmit(): stores skb into tx_skbuff. Note that the first BD
(which is also the last one) isn't marked as ready, yet.
- clean_tx_ring(): sees that skb is not null, *and* its lstatus
says that it is NOT ready (like if BD was sent), so it cleans
it up (bad!)
- start_xmit(): marks BD as ready [to send], but it's too late.
We can fix this simply by reordering lstatus/tx_skbuff writes.
Reported-by: Martyn Welch <martyn.we...@ge.com>
Bisected-by: Paul Gortmaker <paul.gortma...@windriver.com>
Signed-off-by: Anton Vorontsov <avoront...@ru.mvista.com>
Tested-by: Paul Gortmaker <paul.gortma...@windriver.com>
Tested-by: Martyn Welch <martyn.we...@ge.com>
Cc: Sandeep Gopalpet <sandeep.ku...@freescale.com>
Cc: Stable <sta...@vger.kernel.org> [2.6.33]
---
drivers/net/gianfar.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index 8bd3c9f..cccb409 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -2021,7 +2021,6 @@ static int gfar_start_xmit(struct sk_buff *skb, struct
net_device *dev)
}
/* setup the TxBD length and buffer pointer for the first BD */
- tx_queue->tx_skbuff[tx_queue->skb_curtx] = skb;
txbdp_start->bufPtr = dma_map_single(&priv->ofdev->dev, skb->data,
skb_headlen(skb), DMA_TO_DEVICE);
@@ -2053,6 +2052,10 @@ static int gfar_start_xmit(struct sk_buff *skb, struct
net_device *dev)
txbdp_start->lstatus = lstatus;
+ eieio(); /* force lstatus write before tx_skbuff */
+
+ tx_queue->tx_skbuff[tx_queue->skb_curtx] = skb;
+
/* Update the current skb pointer to the next entry we will use
* (wrapping if necessary) */
tx_queue->skb_curtx = (tx_queue->skb_curtx + 1) &
--
1.7.0
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