This is a note to let you know that I've just added the patch titled
net: ethernet: oa_tc6: fix tx skb race condition between reference pointers
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-ethernet-oa_tc6-fix-tx-skb-race-condition-betwee.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit f5f024ec450b5d75b3c00d6a519e1ebc99790c05
Author: Parthiban Veerasooran <parthiban.veerasooran@xxxxxxxxxxxxx>
Date: Fri Dec 13 18:01:59 2024 +0530
net: ethernet: oa_tc6: fix tx skb race condition between reference pointers
[ Upstream commit e592b5110b3e9393881b0a019d86832bbf71a47f ]
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@xxxxxxxxxxxxx>
Reviewed-by: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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;
