diff mbox series

[1/4] ftgmac100: Fix race issue on TX descriptor[0]

Message ID 20201019085717.32413-2-dylan_hung@aspeedtech.com (mailing list archive)
State Not Applicable
Delegated to: Netdev Maintainers
Headers show
Series fix ftgmac100 issues on aspeed soc | expand

Commit Message

Dylan Hung Oct. 19, 2020, 8:57 a.m. UTC
These rules must be followed when accessing the TX descriptor:

1. A TX descriptor is "cleanable" only when its value is non-zero
and the owner bit is set to "software"

2. A TX descriptor is "writable" only when its value is zero regardless
the edotr mask.

Fixes: 52c0cae87465 ("ftgmac100: Remove tx descriptor accessors")
Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
---
 drivers/net/ethernet/faraday/ftgmac100.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

Comments

Benjamin Herrenschmidt Oct. 19, 2020, 11:19 p.m. UTC | #1
On Mon, 2020-10-19 at 16:57 +0800, Dylan Hung wrote:
> These rules must be followed when accessing the TX descriptor:
> 
> 1. A TX descriptor is "cleanable" only when its value is non-zero
> and the owner bit is set to "software"

Can you elaborate ? What is the point of that change ? The owner bit
should be sufficient, why do we need to check other fields ?

> 2. A TX descriptor is "writable" only when its value is zero
> regardless the edotr mask.

Again, why is that ? Can you elaborate ? What race are you trying to
address here ?

Cheers,
Ben.

> Fixes: 52c0cae87465 ("ftgmac100: Remove tx descriptor accessors")
> Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
> Signed-off-by: Joel Stanley <joel@jms.id.au>
> ---
>  drivers/net/ethernet/faraday/ftgmac100.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/net/ethernet/faraday/ftgmac100.c
> b/drivers/net/ethernet/faraday/ftgmac100.c
> index 00024dd41147..7cacbe4aecb7 100644
> --- a/drivers/net/ethernet/faraday/ftgmac100.c
> +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> @@ -647,6 +647,9 @@ static bool ftgmac100_tx_complete_packet(struct
> ftgmac100 *priv)
>  	if (ctl_stat & FTGMAC100_TXDES0_TXDMA_OWN)
>  		return false;
>  
> +	if ((ctl_stat & ~(priv->txdes0_edotr_mask)) == 0)
> +		return false;
> +
>  	skb = priv->tx_skbs[pointer];
>  	netdev->stats.tx_packets++;
>  	netdev->stats.tx_bytes += skb->len;
> @@ -756,6 +759,9 @@ static netdev_tx_t
> ftgmac100_hard_start_xmit(struct sk_buff *skb,
>  	pointer = priv->tx_pointer;
>  	txdes = first = &priv->txdes[pointer];
>  
> +	if (le32_to_cpu(txdes->txdes0) & ~priv->txdes0_edotr_mask)
> +		goto drop;
> +
>  	/* Setup it up with the packet head. Don't write the head to
> the
>  	 * ring just yet
>  	 */
> @@ -787,6 +793,10 @@ static netdev_tx_t
> ftgmac100_hard_start_xmit(struct sk_buff *skb,
>  		/* Setup descriptor */
>  		priv->tx_skbs[pointer] = skb;
>  		txdes = &priv->txdes[pointer];
> +
> +		if (le32_to_cpu(txdes->txdes0) & ~priv-
> >txdes0_edotr_mask)
> +			goto dma_err;
> +
>  		ctl_stat = ftgmac100_base_tx_ctlstat(priv, pointer);
>  		ctl_stat |= FTGMAC100_TXDES0_TXDMA_OWN;
>  		ctl_stat |= FTGMAC100_TXDES0_TXBUF_SIZE(len);
Joel Stanley Oct. 20, 2020, 4:13 a.m. UTC | #2
On Mon, 19 Oct 2020 at 23:20, Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:
>
> On Mon, 2020-10-19 at 16:57 +0800, Dylan Hung wrote:
> > These rules must be followed when accessing the TX descriptor:
> >
> > 1. A TX descriptor is "cleanable" only when its value is non-zero
> > and the owner bit is set to "software"
>
> Can you elaborate ? What is the point of that change ? The owner bit
> should be sufficient, why do we need to check other fields ?

I would like Dylan to clarify too. The datasheet has a footnote below
the descriptor layout:

 - TXDES#0: Bits 27 ~ 14 are valid only when FTS = 1
 - TXDES#1: Bits 31 ~ 0 are valid only when FTS = 1

So the ownership bit (31) is not valid unless FTS is set. However,
this isn't what his patch does. It adds checks for EDOTR.

>
> > 2. A TX descriptor is "writable" only when its value is zero
> > regardless the edotr mask.
>
> Again, why is that ? Can you elaborate ? What race are you trying to
> address here ?
>
> Cheers,
> Ben.
>
> > Fixes: 52c0cae87465 ("ftgmac100: Remove tx descriptor accessors")
> > Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
> > Signed-off-by: Joel Stanley <joel@jms.id.au>
> > ---
> >  drivers/net/ethernet/faraday/ftgmac100.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/faraday/ftgmac100.c
> > b/drivers/net/ethernet/faraday/ftgmac100.c
> > index 00024dd41147..7cacbe4aecb7 100644
> > --- a/drivers/net/ethernet/faraday/ftgmac100.c
> > +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> > @@ -647,6 +647,9 @@ static bool ftgmac100_tx_complete_packet(struct
> > ftgmac100 *priv)
> >       if (ctl_stat & FTGMAC100_TXDES0_TXDMA_OWN)
> >               return false;
> >
> > +     if ((ctl_stat & ~(priv->txdes0_edotr_mask)) == 0)
> > +             return false;
> > +
> >       skb = priv->tx_skbs[pointer];
> >       netdev->stats.tx_packets++;
> >       netdev->stats.tx_bytes += skb->len;
> > @@ -756,6 +759,9 @@ static netdev_tx_t
> > ftgmac100_hard_start_xmit(struct sk_buff *skb,
> >       pointer = priv->tx_pointer;
> >       txdes = first = &priv->txdes[pointer];
> >
> > +     if (le32_to_cpu(txdes->txdes0) & ~priv->txdes0_edotr_mask)
> > +             goto drop;
> > +
> >       /* Setup it up with the packet head. Don't write the head to
> > the
> >        * ring just yet
> >        */
> > @@ -787,6 +793,10 @@ static netdev_tx_t
> > ftgmac100_hard_start_xmit(struct sk_buff *skb,
> >               /* Setup descriptor */
> >               priv->tx_skbs[pointer] = skb;
> >               txdes = &priv->txdes[pointer];
> > +
> > +             if (le32_to_cpu(txdes->txdes0) & ~priv-
> > >txdes0_edotr_mask)
> > +                     goto dma_err;
> > +
> >               ctl_stat = ftgmac100_base_tx_ctlstat(priv, pointer);
> >               ctl_stat |= FTGMAC100_TXDES0_TXDMA_OWN;
> >               ctl_stat |= FTGMAC100_TXDES0_TXBUF_SIZE(len);
>
Benjamin Herrenschmidt Oct. 20, 2020, 6:23 a.m. UTC | #3
On Tue, 2020-10-20 at 04:13 +0000, Joel Stanley wrote:
> On Mon, 19 Oct 2020 at 23:20, Benjamin Herrenschmidt
> <benh@kernel.crashing.org> wrote:
> > 
> > On Mon, 2020-10-19 at 16:57 +0800, Dylan Hung wrote:
> > > These rules must be followed when accessing the TX descriptor:
> > > 
> > > 1. A TX descriptor is "cleanable" only when its value is non-zero
> > > and the owner bit is set to "software"
> > 
> > Can you elaborate ? What is the point of that change ? The owner
> > bit
> > should be sufficient, why do we need to check other fields ?
> 
> I would like Dylan to clarify too. The datasheet has a footnote below
> the descriptor layout:
> 
>  - TXDES#0: Bits 27 ~ 14 are valid only when FTS = 1
>  - TXDES#1: Bits 31 ~ 0 are valid only when FTS = 1
> 
> So the ownership bit (31) is not valid unless FTS is set. However,
> this isn't what his patch does. It adds checks for EDOTR.

No I think it adds a check for everything except EDOTR which just marks
the end of ring and needs to be ignored in the comparison.

That said, we do need a better explanation.

One potential bug I did find by looking at my code however is:

static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv)
{
	struct net_device *netdev = priv->netdev;
	struct ftgmac100_txdes *txdes;
	struct sk_buff *skb;
	unsigned int pointer;
	u32 ctl_stat;

	pointer = priv->tx_clean_pointer;
	txdes = &priv->txdes[pointer];

	ctl_stat = le32_to_cpu(txdes->txdes0);
	if (ctl_stat & FTGMAC100_TXDES0_TXDMA_OWN)
		return false;

	skb = priv->tx_skbs[pointer];
	netdev->stats.tx_packets++;
	netdev->stats.tx_bytes += skb->len;
	ftgmac100_free_tx_packet(priv, pointer, skb, txdes, ctl_stat);
	txdes->txdes0 = cpu_to_le32(ctl_stat & priv->txdes0_edotr_mask);

  ^^^^ There should probably be an smp_wmb() here to ensure that all the above
stores are visible before the tx clean pointer is updated.

	priv->tx_clean_pointer = ftgmac100_next_tx_pointer(priv, pointer);

	return true;
}

Similarly we probablu should have one before setting tx_pointer in start_xmit().

As for the read side of this, I'm not 100% sure, I'll have to think more about
it, it *think* the existing barriers are sufficient at first sight.

Cheers,
Ben.

> > 
> > > 2. A TX descriptor is "writable" only when its value is zero
> > > regardless the edotr mask.
> > 
> > Again, why is that ? Can you elaborate ? What race are you trying
> > to
> > address here ?
> > 
> > Cheers,
> > Ben.
> > 
> > > Fixes: 52c0cae87465 ("ftgmac100: Remove tx descriptor accessors")
> > > Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
> > > Signed-off-by: Joel Stanley <joel@jms.id.au>
> > > ---
> > >  drivers/net/ethernet/faraday/ftgmac100.c | 10 ++++++++++
> > >  1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/drivers/net/ethernet/faraday/ftgmac100.c
> > > b/drivers/net/ethernet/faraday/ftgmac100.c
> > > index 00024dd41147..7cacbe4aecb7 100644
> > > --- a/drivers/net/ethernet/faraday/ftgmac100.c
> > > +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> > > @@ -647,6 +647,9 @@ static bool
> > > ftgmac100_tx_complete_packet(struct
> > > ftgmac100 *priv)
> > >       if (ctl_stat & FTGMAC100_TXDES0_TXDMA_OWN)
> > >               return false;
> > > 
> > > +     if ((ctl_stat & ~(priv->txdes0_edotr_mask)) == 0)
> > > +             return false;
> > > +
> > >       skb = priv->tx_skbs[pointer];
> > >       netdev->stats.tx_packets++;
> > >       netdev->stats.tx_bytes += skb->len;
> > > @@ -756,6 +759,9 @@ static netdev_tx_t
> > > ftgmac100_hard_start_xmit(struct sk_buff *skb,
> > >       pointer = priv->tx_pointer;
> > >       txdes = first = &priv->txdes[pointer];
> > > 
> > > +     if (le32_to_cpu(txdes->txdes0) & ~priv->txdes0_edotr_mask)
> > > +             goto drop;
> > > +
> > >       /* Setup it up with the packet head. Don't write the head
> > > to
> > > the
> > >        * ring just yet
> > >        */
> > > @@ -787,6 +793,10 @@ static netdev_tx_t
> > > ftgmac100_hard_start_xmit(struct sk_buff *skb,
> > >               /* Setup descriptor */
> > >               priv->tx_skbs[pointer] = skb;
> > >               txdes = &priv->txdes[pointer];
> > > +
> > > +             if (le32_to_cpu(txdes->txdes0) & ~priv-
> > > > txdes0_edotr_mask)
> > > 
> > > +                     goto dma_err;
> > > +
> > >               ctl_stat = ftgmac100_base_tx_ctlstat(priv,
> > > pointer);
> > >               ctl_stat |= FTGMAC100_TXDES0_TXDMA_OWN;
> > >               ctl_stat |= FTGMAC100_TXDES0_TXBUF_SIZE(len);
Joel Stanley Oct. 20, 2020, 7:13 a.m. UTC | #4
On Tue, 20 Oct 2020 at 06:23, Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:
>
> On Tue, 2020-10-20 at 04:13 +0000, Joel Stanley wrote:
> > On Mon, 19 Oct 2020 at 23:20, Benjamin Herrenschmidt
> > <benh@kernel.crashing.org> wrote:
> > >
> > > On Mon, 2020-10-19 at 16:57 +0800, Dylan Hung wrote:
> > > > These rules must be followed when accessing the TX descriptor:
> > > >
> > > > 1. A TX descriptor is "cleanable" only when its value is non-zero
> > > > and the owner bit is set to "software"
> > >
> > > Can you elaborate ? What is the point of that change ? The owner
> > > bit
> > > should be sufficient, why do we need to check other fields ?
> >
> > I would like Dylan to clarify too. The datasheet has a footnote below
> > the descriptor layout:
> >
> >  - TXDES#0: Bits 27 ~ 14 are valid only when FTS = 1
> >  - TXDES#1: Bits 31 ~ 0 are valid only when FTS = 1
> >
> > So the ownership bit (31) is not valid unless FTS is set. However,
> > this isn't what his patch does. It adds checks for EDOTR.
>
> No I think it adds a check for everything except EDOTR which just marks
> the end of ring and needs to be ignored in the comparison.

Of course. I missed the invert.

I did some testing with just this patch (and "[4/4] ftgmac100: Restart
MAC HW once") from Dylan. It seemed to resolve the hang, but there
were occasional retries. Putting in some tracing I only hit the
condition in ftgmac100_tx_complete_packet, never in
ftgmac100_hard_start_xmit.

> That said, we do need a better explanation.
>
> One potential bug I did find by looking at my code however is:
>
> static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv)
> {
>         struct net_device *netdev = priv->netdev;
>         struct ftgmac100_txdes *txdes;
>         struct sk_buff *skb;
>         unsigned int pointer;
>         u32 ctl_stat;
>
>         pointer = priv->tx_clean_pointer;
>         txdes = &priv->txdes[pointer];
>
>         ctl_stat = le32_to_cpu(txdes->txdes0);
>         if (ctl_stat & FTGMAC100_TXDES0_TXDMA_OWN)
>                 return false;
>
>         skb = priv->tx_skbs[pointer];
>         netdev->stats.tx_packets++;
>         netdev->stats.tx_bytes += skb->len;
>         ftgmac100_free_tx_packet(priv, pointer, skb, txdes, ctl_stat);
>         txdes->txdes0 = cpu_to_le32(ctl_stat & priv->txdes0_edotr_mask);
>
>   ^^^^ There should probably be an smp_wmb() here to ensure that all the above
> stores are visible before the tx clean pointer is updated.
>
>         priv->tx_clean_pointer = ftgmac100_next_tx_pointer(priv, pointer);
>
>         return true;
> }
>
> Similarly we probablu should have one before setting tx_pointer in start_xmit().

I added the two smp_wmb you suggested (with only 4/4 applied). This
did the trick; iperf on a gigabit link is running well with no
retries.

diff --git a/drivers/net/ethernet/faraday/ftgmac100.c
b/drivers/net/ethernet/faraday/ftgmac100.c
index 331d4bdd4a67..15cdfeb135b0 100644
--- a/drivers/net/ethernet/faraday/ftgmac100.c
+++ b/drivers/net/ethernet/faraday/ftgmac100.c
@@ -653,6 +653,11 @@ static bool ftgmac100_tx_complete_packet(struct
ftgmac100 *priv)
     ftgmac100_free_tx_packet(priv, pointer, skb, txdes, ctl_stat);
     txdes->txdes0 = cpu_to_le32(ctl_stat & priv->txdes0_edotr_mask);

+    /* Ensure the descriptor config is visible before setting the tx
+     * pointer.
+     */
+    smp_wmb();
+
     priv->tx_clean_pointer = ftgmac100_next_tx_pointer(priv, pointer);

     return true;
@@ -806,6 +811,11 @@ static netdev_tx_t
ftgmac100_hard_start_xmit(struct sk_buff *skb,
     dma_wmb();
     first->txdes0 = cpu_to_le32(f_ctl_stat);

+    /* Ensure the descriptor config is visible before setting the tx
+     * pointer.
+     */
+    smp_wmb();
+
     /* Update next TX pointer */
     priv->tx_pointer = pointer;

I left the test running while writing this email and I did start to
see some retries. I'm not sure if that's because my laptop is one of
the test machines, or if we have another issue.

I will do some further testing over night.

Cheers,

Joel

>
> As for the read side of this, I'm not 100% sure, I'll have to think more about
> it, it *think* the existing barriers are sufficient at first sight.
>
> Cheers,
> Ben.
>
> > >
> > > > 2. A TX descriptor is "writable" only when its value is zero
> > > > regardless the edotr mask.
> > >
> > > Again, why is that ? Can you elaborate ? What race are you trying
> > > to
> > > address here ?
> > >
> > > Cheers,
> > > Ben.
> > >
> > > > Fixes: 52c0cae87465 ("ftgmac100: Remove tx descriptor accessors")
> > > > Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
> > > > Signed-off-by: Joel Stanley <joel@jms.id.au>
> > > > ---
> > > >  drivers/net/ethernet/faraday/ftgmac100.c | 10 ++++++++++
> > > >  1 file changed, 10 insertions(+)
> > > >
> > > > diff --git a/drivers/net/ethernet/faraday/ftgmac100.c
> > > > b/drivers/net/ethernet/faraday/ftgmac100.c
> > > > index 00024dd41147..7cacbe4aecb7 100644
> > > > --- a/drivers/net/ethernet/faraday/ftgmac100.c
> > > > +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> > > > @@ -647,6 +647,9 @@ static bool
> > > > ftgmac100_tx_complete_packet(struct
> > > > ftgmac100 *priv)
> > > >       if (ctl_stat & FTGMAC100_TXDES0_TXDMA_OWN)
> > > >               return false;
> > > >
> > > > +     if ((ctl_stat & ~(priv->txdes0_edotr_mask)) == 0)
> > > > +             return false;
> > > > +
> > > >       skb = priv->tx_skbs[pointer];
> > > >       netdev->stats.tx_packets++;
> > > >       netdev->stats.tx_bytes += skb->len;
> > > > @@ -756,6 +759,9 @@ static netdev_tx_t
> > > > ftgmac100_hard_start_xmit(struct sk_buff *skb,
> > > >       pointer = priv->tx_pointer;
> > > >       txdes = first = &priv->txdes[pointer];
> > > >
> > > > +     if (le32_to_cpu(txdes->txdes0) & ~priv->txdes0_edotr_mask)
> > > > +             goto drop;
> > > > +
> > > >       /* Setup it up with the packet head. Don't write the head
> > > > to
> > > > the
> > > >        * ring just yet
> > > >        */
> > > > @@ -787,6 +793,10 @@ static netdev_tx_t
> > > > ftgmac100_hard_start_xmit(struct sk_buff *skb,
> > > >               /* Setup descriptor */
> > > >               priv->tx_skbs[pointer] = skb;
> > > >               txdes = &priv->txdes[pointer];
> > > > +
> > > > +             if (le32_to_cpu(txdes->txdes0) & ~priv-
> > > > > txdes0_edotr_mask)
> > > >
> > > > +                     goto dma_err;
> > > > +
> > > >               ctl_stat = ftgmac100_base_tx_ctlstat(priv,
> > > > pointer);
> > > >               ctl_stat |= FTGMAC100_TXDES0_TXDMA_OWN;
> > > >               ctl_stat |= FTGMAC100_TXDES0_TXBUF_SIZE(len);
>
diff mbox series

Patch

diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
index 00024dd41147..7cacbe4aecb7 100644
--- a/drivers/net/ethernet/faraday/ftgmac100.c
+++ b/drivers/net/ethernet/faraday/ftgmac100.c
@@ -647,6 +647,9 @@  static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv)
 	if (ctl_stat & FTGMAC100_TXDES0_TXDMA_OWN)
 		return false;
 
+	if ((ctl_stat & ~(priv->txdes0_edotr_mask)) == 0)
+		return false;
+
 	skb = priv->tx_skbs[pointer];
 	netdev->stats.tx_packets++;
 	netdev->stats.tx_bytes += skb->len;
@@ -756,6 +759,9 @@  static netdev_tx_t ftgmac100_hard_start_xmit(struct sk_buff *skb,
 	pointer = priv->tx_pointer;
 	txdes = first = &priv->txdes[pointer];
 
+	if (le32_to_cpu(txdes->txdes0) & ~priv->txdes0_edotr_mask)
+		goto drop;
+
 	/* Setup it up with the packet head. Don't write the head to the
 	 * ring just yet
 	 */
@@ -787,6 +793,10 @@  static netdev_tx_t ftgmac100_hard_start_xmit(struct sk_buff *skb,
 		/* Setup descriptor */
 		priv->tx_skbs[pointer] = skb;
 		txdes = &priv->txdes[pointer];
+
+		if (le32_to_cpu(txdes->txdes0) & ~priv->txdes0_edotr_mask)
+			goto dma_err;
+
 		ctl_stat = ftgmac100_base_tx_ctlstat(priv, pointer);
 		ctl_stat |= FTGMAC100_TXDES0_TXDMA_OWN;
 		ctl_stat |= FTGMAC100_TXDES0_TXBUF_SIZE(len);