[PATCH net v4 0/2] Fixes on the OPEN Alliance TC6 10BASE-T1x MAC-PHY support generic lib

[PATCH net v4 0/2] Fixes on the OPEN Alliance TC6 10BASE-T1x MAC-PHY support generic lib

[Parthiban Veerasooran]

This patch series contain the below fixes.

- Infinite loop error when tx credits becomes 0.
- Race condition between tx skb reference pointers.

v2:
- Added mutex lock to protect tx skb reference handling.

v3:
- Added mutex protection in assigning new tx skb to waiting_tx_skb
  pointer.
- Explained the possible scenario for the race condition with the time
  diagram in the commit message.

v4:
- Replaced mutex with spin_lock_bh() variants as the start_xmit runs in
  BH/softirq context which can't take sleeping locks.


Parthiban Veerasooran (2):
  net: ethernet: oa_tc6: fix infinite loop error when tx credits becomes
    0
  net: ethernet: oa_tc6: fix tx skb race condition between reference
    pointers

 drivers/net/ethernet/oa_tc6.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)


base-commit: 2c27c7663390d28bc71e97500eb68e0ce2a7223f
-- 
2.34.1

[PATCH net v4 1/2] net: ethernet: oa_tc6: fix infinite loop error when tx credits becomes 0

[Parthiban Veerasooran]

SPI thread wakes up to perform SPI transfer whenever there is an TX skb
from n/w stack or interrupt from MAC-PHY. Ethernet frame from TX skb is
transferred based on the availability tx credits in the MAC-PHY which is
reported from the previous SPI transfer. Sometimes there is a possibility
that TX skb is available to transmit but there is no tx credits from
MAC-PHY. In this case, there will not be any SPI transfer but the thread
will be running in an endless loop until tx credits available again.

So checking the availability of tx credits along with TX skb will prevent
the above infinite loop. When the tx credits available again that will be
notified through interrupt which will trigger the SPI transfer to get the
available tx credits.

Fixes: 53fbde8ab21e ("net: ethernet: oa_tc6: implement transmit path to transfer tx ethernet frames")
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Parthiban Veerasooran <parthiban.veerasooran@microchip.com>
---
 drivers/net/ethernet/oa_tc6.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/oa_tc6.c b/drivers/net/ethernet/oa_tc6.c
index f9c0dcd965c2..4c8b0ca922b7 100644
--- a/drivers/net/ethernet/oa_tc6.c
+++ b/drivers/net/ethernet/oa_tc6.c
@@ -1111,8 +1111,9 @@ static int oa_tc6_spi_thread_handler(void *data)
 		/* This kthread will be waken up if there is a tx skb or mac-phy
 		 * interrupt to perform spi transfer with tx chunks.
 		 */
-		wait_event_interruptible(tc6->spi_wq, tc6->waiting_tx_skb ||
-					 tc6->int_flag ||
+		wait_event_interruptible(tc6->spi_wq, tc6->int_flag ||
+					 (tc6->waiting_tx_skb &&
+					 tc6->tx_credits) ||
 					 kthread_should_stop());
 
 		if (kthread_should_stop())
-- 
2.34.1

[PATCH net v4 2/2] net: ethernet: oa_tc6: fix tx skb race condition between reference pointers

[Parthiban Veerasooran]

There are two skb pointers to manage tx skb's enqueued from n/w stack.
waiting_tx_skb pointer points to the tx skb which needs to be processed
and ongoing_tx_skb pointer points to the tx skb which is being processed.

SPI thread prepares the tx data chunks from the tx skb pointed by the
ongoing_tx_skb pointer. When the tx skb pointed by the ongoing_tx_skb is
processed, the tx skb pointed by the waiting_tx_skb is assigned to
ongoing_tx_skb and the waiting_tx_skb pointer is assigned with NULL.
Whenever there is a new tx skb from n/w stack, it will be assigned to
waiting_tx_skb pointer if it is NULL. Enqueuing and processing of a tx skb
handled in two different threads.

Consider a scenario where the SPI thread processed an ongoing_tx_skb and
it moves next tx skb from waiting_tx_skb pointer to ongoing_tx_skb pointer
without doing any NULL check. At this time, if the waiting_tx_skb pointer
is NULL then ongoing_tx_skb pointer is also assigned with NULL. After
that, if a new tx skb is assigned to waiting_tx_skb pointer by the n/w
stack and there is a chance to overwrite the tx skb pointer with NULL in
the SPI thread. Finally one of the tx skb will be left as unhandled,
resulting packet missing and memory leak.

- Consider the below scenario where the TXC reported from the previous
transfer is 10 and ongoing_tx_skb holds an tx ethernet frame which can be
transported in 20 TXCs and waiting_tx_skb is still NULL.
	tx_credits = 10; /* 21 are filled in the previous transfer */
	ongoing_tx_skb = 20;
	waiting_tx_skb = NULL; /* Still NULL */
- So, (tc6->ongoing_tx_skb || tc6->waiting_tx_skb) becomes true.
- After oa_tc6_prepare_spi_tx_buf_for_tx_skbs()
	ongoing_tx_skb = 10;
	waiting_tx_skb = NULL; /* Still NULL */
- Perform SPI transfer.
- Process SPI rx buffer to get the TXC from footers.
- Now let's assume previously filled 21 TXCs are freed so we are good to
transport the next remaining 10 tx chunks from ongoing_tx_skb.
	tx_credits = 21;
	ongoing_tx_skb = 10;
	waiting_tx_skb = NULL;
- So, (tc6->ongoing_tx_skb || tc6->waiting_tx_skb) becomes true again.
- In the oa_tc6_prepare_spi_tx_buf_for_tx_skbs()
	ongoing_tx_skb = NULL;
	waiting_tx_skb = NULL;

- Now the below bad case might happen,

Thread1 (oa_tc6_start_xmit)	Thread2 (oa_tc6_spi_thread_handler)
---------------------------	-----------------------------------
- if waiting_tx_skb is NULL
				- if ongoing_tx_skb is NULL
				- ongoing_tx_skb = waiting_tx_skb
- waiting_tx_skb = skb
				- waiting_tx_skb = NULL
				...
				- ongoing_tx_skb = NULL
- if waiting_tx_skb is NULL
- waiting_tx_skb = skb

To overcome the above issue, protect the moving of tx skb reference from
waiting_tx_skb pointer to ongoing_tx_skb pointer and assigning new tx skb
to waiting_tx_skb pointer, so that the other thread can't access the
waiting_tx_skb pointer until the current thread completes moving the tx
skb reference safely.

Fixes: 53fbde8ab21e ("net: ethernet: oa_tc6: implement transmit path to transfer tx ethernet frames")
Signed-off-by: Parthiban Veerasooran <parthiban.veerasooran@microchip.com>
---
 drivers/net/ethernet/oa_tc6.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/oa_tc6.c b/drivers/net/ethernet/oa_tc6.c
index 4c8b0ca922b7..db200e4ec284 100644
--- a/drivers/net/ethernet/oa_tc6.c
+++ b/drivers/net/ethernet/oa_tc6.c
@@ -113,6 +113,7 @@ struct oa_tc6 {
 	struct mii_bus *mdiobus;
 	struct spi_device *spi;
 	struct mutex spi_ctrl_lock; /* Protects spi control transfer */
+	spinlock_t tx_skb_lock; /* Protects tx skb handling */
 	void *spi_ctrl_tx_buf;
 	void *spi_ctrl_rx_buf;
 	void *spi_data_tx_buf;
@@ -1004,8 +1005,10 @@ static u16 oa_tc6_prepare_spi_tx_buf_for_tx_skbs(struct oa_tc6 *tc6)
 	for (used_tx_credits = 0; used_tx_credits < tc6->tx_credits;
 	     used_tx_credits++) {
 		if (!tc6->ongoing_tx_skb) {
+			spin_lock_bh(&tc6->tx_skb_lock);
 			tc6->ongoing_tx_skb = tc6->waiting_tx_skb;
 			tc6->waiting_tx_skb = NULL;
+			spin_unlock_bh(&tc6->tx_skb_lock);
 		}
 		if (!tc6->ongoing_tx_skb)
 			break;
@@ -1210,7 +1213,9 @@ netdev_tx_t oa_tc6_start_xmit(struct oa_tc6 *tc6, struct sk_buff *skb)
 		return NETDEV_TX_OK;
 	}
 
+	spin_lock_bh(&tc6->tx_skb_lock);
 	tc6->waiting_tx_skb = skb;
+	spin_unlock_bh(&tc6->tx_skb_lock);
 
 	/* Wake spi kthread to perform spi transfer */
 	wake_up_interruptible(&tc6->spi_wq);
@@ -1240,6 +1245,7 @@ struct oa_tc6 *oa_tc6_init(struct spi_device *spi, struct net_device *netdev)
 	tc6->netdev = netdev;
 	SET_NETDEV_DEV(netdev, &spi->dev);
 	mutex_init(&tc6->spi_ctrl_lock);
+	spin_lock_init(&tc6->tx_skb_lock);
 
 	/* Set the SPI controller to pump at realtime priority */
 	tc6->spi->rt = true;
-- 
2.34.1

Re: [PATCH net v4 2/2] net: ethernet: oa_tc6: fix tx skb race condition between reference pointers

[Larysa Zaremba]

On Fri, Dec 13, 2024 at 06:01:59PM +0530, Parthiban Veerasooran wrote:
> There are two skb pointers to manage tx skb's enqueued from n/w stack.
> waiting_tx_skb pointer points to the tx skb which needs to be processed
> and ongoing_tx_skb pointer points to the tx skb which is being processed.
> 
> SPI thread prepares the tx data chunks from the tx skb pointed by the
> ongoing_tx_skb pointer. When the tx skb pointed by the ongoing_tx_skb is
> processed, the tx skb pointed by the waiting_tx_skb is assigned to
> ongoing_tx_skb and the waiting_tx_skb pointer is assigned with NULL.
> Whenever there is a new tx skb from n/w stack, it will be assigned to
> waiting_tx_skb pointer if it is NULL. Enqueuing and processing of a tx skb
> handled in two different threads.
> 
> Consider a scenario where the SPI thread processed an ongoing_tx_skb and
> it moves next tx skb from waiting_tx_skb pointer to ongoing_tx_skb pointer
> without doing any NULL check. At this time, if the waiting_tx_skb pointer
> is NULL then ongoing_tx_skb pointer is also assigned with NULL. After
> that, if a new tx skb is assigned to waiting_tx_skb pointer by the n/w
> stack and there is a chance to overwrite the tx skb pointer with NULL in
> the SPI thread. Finally one of the tx skb will be left as unhandled,
> resulting packet missing and memory leak.
> 
> - Consider the below scenario where the TXC reported from the previous
> transfer is 10 and ongoing_tx_skb holds an tx ethernet frame which can be
> transported in 20 TXCs and waiting_tx_skb is still NULL.
> 	tx_credits = 10; /* 21 are filled in the previous transfer */
> 	ongoing_tx_skb = 20;
> 	waiting_tx_skb = NULL; /* Still NULL */
> - So, (tc6->ongoing_tx_skb || tc6->waiting_tx_skb) becomes true.
> - After oa_tc6_prepare_spi_tx_buf_for_tx_skbs()
> 	ongoing_tx_skb = 10;
> 	waiting_tx_skb = NULL; /* Still NULL */
> - Perform SPI transfer.
> - Process SPI rx buffer to get the TXC from footers.
> - Now let's assume previously filled 21 TXCs are freed so we are good to
> transport the next remaining 10 tx chunks from ongoing_tx_skb.
> 	tx_credits = 21;
> 	ongoing_tx_skb = 10;
> 	waiting_tx_skb = NULL;
> - So, (tc6->ongoing_tx_skb || tc6->waiting_tx_skb) becomes true again.
> - In the oa_tc6_prepare_spi_tx_buf_for_tx_skbs()
> 	ongoing_tx_skb = NULL;
> 	waiting_tx_skb = NULL;
> 
> - Now the below bad case might happen,
> 
> Thread1 (oa_tc6_start_xmit)	Thread2 (oa_tc6_spi_thread_handler)
> ---------------------------	-----------------------------------
> - if waiting_tx_skb is NULL
> 				- if ongoing_tx_skb is NULL
> 				- ongoing_tx_skb = waiting_tx_skb
> - waiting_tx_skb = skb
> 				- waiting_tx_skb = NULL
> 				...
> 				- ongoing_tx_skb = NULL
> - if waiting_tx_skb is NULL
> - waiting_tx_skb = skb
> 
> To overcome the above issue, protect the moving of tx skb reference from
> waiting_tx_skb pointer to ongoing_tx_skb pointer and assigning new tx skb
> to waiting_tx_skb pointer, so that the other thread can't access the
> waiting_tx_skb pointer until the current thread completes moving the tx
> skb reference safely.
>

This fixes the above race condition and spin_lock_bh() is appropriate.

Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
 
> Fixes: 53fbde8ab21e ("net: ethernet: oa_tc6: implement transmit path to transfer tx ethernet frames")
> Signed-off-by: Parthiban Veerasooran <parthiban.veerasooran@microchip.com>
> ---
>  drivers/net/ethernet/oa_tc6.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/oa_tc6.c b/drivers/net/ethernet/oa_tc6.c
> index 4c8b0ca922b7..db200e4ec284 100644
> --- a/drivers/net/ethernet/oa_tc6.c
> +++ b/drivers/net/ethernet/oa_tc6.c
> @@ -113,6 +113,7 @@ struct oa_tc6 {
>  	struct mii_bus *mdiobus;
>  	struct spi_device *spi;
>  	struct mutex spi_ctrl_lock; /* Protects spi control transfer */
> +	spinlock_t tx_skb_lock; /* Protects tx skb handling */
>  	void *spi_ctrl_tx_buf;
>  	void *spi_ctrl_rx_buf;
>  	void *spi_data_tx_buf;
> @@ -1004,8 +1005,10 @@ static u16 oa_tc6_prepare_spi_tx_buf_for_tx_skbs(struct oa_tc6 *tc6)
>  	for (used_tx_credits = 0; used_tx_credits < tc6->tx_credits;
>  	     used_tx_credits++) {
>  		if (!tc6->ongoing_tx_skb) {
> +			spin_lock_bh(&tc6->tx_skb_lock);
>  			tc6->ongoing_tx_skb = tc6->waiting_tx_skb;
>  			tc6->waiting_tx_skb = NULL;
> +			spin_unlock_bh(&tc6->tx_skb_lock);
>  		}
>  		if (!tc6->ongoing_tx_skb)
>  			break;
> @@ -1210,7 +1213,9 @@ netdev_tx_t oa_tc6_start_xmit(struct oa_tc6 *tc6, struct sk_buff *skb)
>  		return NETDEV_TX_OK;
>  	}
>  
> +	spin_lock_bh(&tc6->tx_skb_lock);
>  	tc6->waiting_tx_skb = skb;
> +	spin_unlock_bh(&tc6->tx_skb_lock);
>  
>  	/* Wake spi kthread to perform spi transfer */
>  	wake_up_interruptible(&tc6->spi_wq);
> @@ -1240,6 +1245,7 @@ struct oa_tc6 *oa_tc6_init(struct spi_device *spi, struct net_device *netdev)
>  	tc6->netdev = netdev;
>  	SET_NETDEV_DEV(netdev, &spi->dev);
>  	mutex_init(&tc6->spi_ctrl_lock);
> +	spin_lock_init(&tc6->tx_skb_lock);
>  
>  	/* Set the SPI controller to pump at realtime priority */
>  	tc6->spi->rt = true;
> -- 
> 2.34.1
> 
> 

Re: [PATCH net v4 0/2] Fixes on the OPEN Alliance TC6 10BASE-T1x MAC-PHY support generic lib

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Fri, 13 Dec 2024 18:01:57 +0530 you wrote:
> This patch series contain the below fixes.
> 
> - Infinite loop error when tx credits becomes 0.
> - Race condition between tx skb reference pointers.
> 
> v2:
> - Added mutex lock to protect tx skb reference handling.
> 
> [...]

Here is the summary with links:
  - [net,v4,1/2] net: ethernet: oa_tc6: fix infinite loop error when tx credits becomes 0
    https://git.kernel.org/netdev/net/c/7d2f320e1274
  - [net,v4,2/2] net: ethernet: oa_tc6: fix tx skb race condition between reference pointers
    https://git.kernel.org/netdev/net/c/e592b5110b3e

You are awesome, thank you!
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