Re: [PATCH] gianfar: Fix TX ring processing on SMP machines
On Wed, Mar 3, 2010 at 8:18 PM, Anton Vorontsov
wrote:
> 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
> Bisected-by: Paul Gortmaker
> Signed-off-by: Anton Vorontsov
> Tested-by: Paul Gortmaker
> Tested-by: Martyn Welch
> Cc: Sandeep Gopalpet
> Cc: Stable [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) &
This patch also makes gianfar work stable on mpc8313 with 2.6.33/RT_PREEMPT.
WIthout it, I see exactly the same problems as reported by Anton on SMP.
/Esben
--
Esben Haabendal, Senior Software Consultant
DoréDevelopment ApS, Ved Stranden 1, 9560 Hadsund, DK-Denmark
Phone: +45 51 92 53 93, E-mail: e...@doredevelopment.dk
WWW: http://www.doredevelopment.dk
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Re: [PATCH] gianfar: Fix TX ring processing on SMP machines
On Mar 4, 2010, at 2:41 AM, David Miller wrote:
> From: Anton Vorontsov
> Date: Wed, 3 Mar 2010 21:18:58 +0300
>
>> 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
>> Bisected-by: Paul Gortmaker
>> Signed-off-by: Anton Vorontsov
>> Tested-by: Paul Gortmaker
>> Tested-by: Martyn Welch
>
> Applied.
Anton,
Once this makes it into Linus's tree can you make sure we get it added to
-stable.
- k
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Re: [PATCH] gianfar: Fix TX ring processing on SMP machines
From: Anton Vorontsov
Date: Wed, 3 Mar 2010 21:18:58 +0300
> 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
> Bisected-by: Paul Gortmaker
> Signed-off-by: Anton Vorontsov
> Tested-by: Paul Gortmaker
> Tested-by: Martyn Welch
Applied.
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[PATCH] gianfar: Fix TX ring processing on SMP machines
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
Bisected-by: Paul Gortmaker
Signed-off-by: Anton Vorontsov
Tested-by: Paul Gortmaker
Tested-by: Martyn Welch
Cc: Sandeep Gopalpet
Cc: Stable [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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