| Message ID | 20241213123159.439739-3-parthiban.veerasooran@microchip.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | e592b5110b3e9393881b0a019d86832bbf71a47f |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | Fixes on the OPEN Alliance TC6 10BASE-T1x MAC-PHY support generic lib | expand |
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 > >
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;
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(+)