@@ -113,6 +113,7 @@ struct oa_tc6 {
struct mii_bus *mdiobus;
struct spi_device *spi;
struct mutex spi_ctrl_lock; /* Protects spi control transfer */
+ struct mutex 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) {
+ mutex_lock(&tc6->tx_skb_lock);
tc6->ongoing_tx_skb = tc6->waiting_tx_skb;
tc6->waiting_tx_skb = NULL;
+ mutex_unlock(&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;
}
+ mutex_lock(&tc6->tx_skb_lock);
tc6->waiting_tx_skb = skb;
+ mutex_unlock(&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);
+ mutex_init(&tc6->tx_skb_lock);
/* Set the SPI controller to pump at realtime priority */
tc6->spi->rt = true;
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(+)