On Fri, Feb 26, 2010 at 11:27:42AM -0500, Paul Gortmaker wrote:
> On 10-02-26 11:10 AM, Anton Vorontsov wrote:
> > On Fri, Feb 26, 2010 at 03:34:07PM +0000, Martyn Welch wrote:
> > [...]
> >> Out of 10 boot attempts, 7 failed.
> >
> > OK, I see why. With ip=on (dhcp boot) it's much harder to trigger
> > it. With static ip config can I see the same.
>
> I'd kind of expected to see us stuck in gianfar on that lock, but
> the SysRQ-T doesn't show us hung up anywhere in gianfar itself.
> [This was on a base 2.6.33, with just a small sysrq fix patch]
> [df841a30] [c0009fc4] __switch_to+0x8c/0xf8
>
> [df841a50] [c0350160] schedule+0x354/0x92c
>
> [df841ae0] [c0331394] rpc_wait_bit_killable+0x2c/0x54
>
> [df841af0] [c0350eb0] __wait_on_bit+0x9c/0x108
>
> [df841b10] [c0350fc0] out_of_line_wait_on_bit+0xa4/0xb4
>
> [df841b40] [c0331cf0] __rpc_execute+0x16c/0x398
>
> [df841b90] [c0329abc] rpc_run_task+0x48/0x9c
>
> [df841ba0] [c0329c40] rpc_call_sync+0x54/0x88
>
> [df841bd0] [c015e780] nfs_proc_lookup+0x94/0xe8
>
> [df841c20] [c014eb60] nfs_lookup+0x12c/0x230
>
> [df841d50] [c00b9680] do_lookup+0x118/0x288
>
> [df841d80] [c00bb904] link_path_walk+0x194/0x1118
>
> [df841df0] [c00bcb08] path_walk+0x8c/0x168
>
> [df841e20] [c00bcd6c] do_path_lookup+0x74/0x7c
>
> [df841e40] [c00be148] do_filp_open+0x5d4/0xba4
>
> [df841f10] [c00abe94] do_sys_open+0xac/0x190
>
Yeah, I don't think this is gianfar-related. It must be something
else triggered by the fact that gianfar no longer sends stuff.
OK, I think I found what's happening in gianfar.
Some background...
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.
It works flawlessly on my p2020, please try it.
Thanks!
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) &
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