[PATCH v2 2/3] can: kvaser_pciefd: Fix echo_skb race conditions

Axel Forsman
2025-05-13T15:10:15Z

The functions kvaser_pciefd_start_xmit() and
kvaser_pciefd_handle_ack_packet() raced to stop/wake TX queues and
get/put echo skbs, as kvaser_pciefd_can->echo_lock was only ever taken
when transmitting. E.g., this caused the following error:

can_put_echo_skb: BUG! echo_skb 5 is occupied!

Instead, use the synchronization helpers in netdev_queues.h. As those
piggyback on BQL barriers, start updating in-flight packets and bytes
counts as well.

Cc: stable@vger.kernel.org
Signed-off-by: Axel Forsman <axfo@kvaser.com>
Tested-by: Jimmy Assarsson <extja@kvaser.com>
Reviewed-by: Jimmy Assarsson <extja@kvaser.com>
---
drivers/net/can/kvaser_pciefd.c | 91 +++++++++++++++++++++------------
1 file changed, 57 insertions(+), 34 deletions(-)

diff --git a/drivers/net/can/kvaser_pciefd.c b/drivers/net/can/kvaser_pciefd.c
index 4d84f7d13c6f..6cb657018cdf 100644
--- a/drivers/net/can/kvaser_pciefd.c
+++ b/drivers/net/can/kvaser_pciefd.c
@@ -16,6 +16,7 @@
#include <linux/netdevice.h>
#include <linux/pci.h>
#include <linux/timer.h>
+#include <net/netdev_queues.h>

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Kvaser AB <support@kvaser.com>");
@@ -410,10 +411,13 @@ struct kvaser_pciefd_can {
void __iomem *reg_base;
struct can_berr_counter bec;
u8 cmd_seq;
+ u8 tx_max_count;
+ u8 tx_idx;
+ u8 ack_idx;
int err_rep_cnt;
- int echo_idx;
+ unsigned int completed_tx_pkts;
+ unsigned int completed_tx_bytes;
spinlock_t lock; /* Locks sensitive registers (e.g. MODE) */
- spinlock_t echo_lock; /* Locks the message echo buffer */
struct timer_list bec_poll_timer;
struct completion start_comp, flush_comp;
};
@@ -714,6 +718,9 @@ static int kvaser_pciefd_open(struct net_device *netdev)
int ret;
struct kvaser_pciefd_can *can = netdev_priv(netdev);

+ can->tx_idx = 0;
+ can->ack_idx = 0;
+
ret = open_candev(netdev);
if (ret)
return ret;
@@ -745,21 +752,26 @@ static int kvaser_pciefd_stop(struct net_device *netdev)
del_timer(&can->bec_poll_timer);
}
can->can.state = CAN_STATE_STOPPED;
+ netdev_reset_queue(netdev);
close_candev(netdev);

return ret;
}

+static unsigned int kvaser_pciefd_tx_avail(const struct kvaser_pciefd_can *can)
+{
+ return can->tx_max_count - (READ_ONCE(can->tx_idx) - READ_ONCE(can->ack_idx));
+}
+
static int kvaser_pciefd_prepare_tx_packet(struct kvaser_pciefd_tx_packet *p,
- struct kvaser_pciefd_can *can,
+ struct can_priv *can, u8 seq,
struct sk_buff *skb)
{
struct canfd_frame *cf = (struct canfd_frame *)skb->data;
int packet_size;
- int seq = can->echo_idx;

memset(p, 0, sizeof(*p));
- if (can->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT)
+ if (can->ctrlmode & CAN_CTRLMODE_ONE_SHOT)
p->header[1] |= KVASER_PCIEFD_TPACKET_SMS;

if (cf->can_id & CAN_RTR_FLAG)
@@ -782,7 +794,7 @@ static int kvaser_pciefd_prepare_tx_packet(struct kvaser_pciefd_tx_packet *p,
} else {
p->header[1] |=
FIELD_PREP(KVASER_PCIEFD_RPACKET_DLC_MASK,
- can_get_cc_dlc((struct can_frame *)cf, can->can.ctrlmode));
+ can_get_cc_dlc((struct can_frame *)cf, can->ctrlmode));
}

p->header[1] |= FIELD_PREP(KVASER_PCIEFD_PACKET_SEQ_MASK, seq);
@@ -797,22 +809,24 @@ static netdev_tx_t kvaser_pciefd_start_xmit(struct sk_buff *skb,
struct net_device *netdev)
{
struct kvaser_pciefd_can *can = netdev_priv(netdev);
- unsigned long irq_flags;
struct kvaser_pciefd_tx_packet packet;
+ unsigned int seq = can->tx_idx & (can->can.echo_skb_max - 1);
+ unsigned int frame_len;
int nr_words;
- u8 count;

if (can_dev_dropped_skb(netdev, skb))
return NETDEV_TX_OK;
+ if (!netif_subqueue_maybe_stop(netdev, 0, kvaser_pciefd_tx_avail(can), 1, 1))
+ return NETDEV_TX_BUSY;

- nr_words = kvaser_pciefd_prepare_tx_packet(&packet, can, skb);
+ nr_words = kvaser_pciefd_prepare_tx_packet(&packet, &can->can, seq, skb);

- spin_lock_irqsave(&can->echo_lock, irq_flags);
/* Prepare and save echo skb in internal slot */
- can_put_echo_skb(skb, netdev, can->echo_idx, 0);
-
- /* Move echo index to the next slot */
- can->echo_idx = (can->echo_idx + 1) % can->can.echo_skb_max;
+ WRITE_ONCE(can->can.echo_skb[seq], NULL);
+ frame_len = can_skb_get_frame_len(skb);
+ can_put_echo_skb(skb, netdev, seq, frame_len);
+ netdev_sent_queue(netdev, frame_len);
+ WRITE_ONCE(can->tx_idx, can->tx_idx + 1);

/* Write header to fifo */
iowrite32(packet.header[0],
@@ -836,14 +850,7 @@ static netdev_tx_t kvaser_pciefd_start_xmit(struct sk_buff *skb,
KVASER_PCIEFD_KCAN_FIFO_LAST_REG);
}

- count = FIELD_GET(KVASER_PCIEFD_KCAN_TX_NR_PACKETS_CURRENT_MASK,
- ioread32(can->reg_base + KVASER_PCIEFD_KCAN_TX_NR_PACKETS_REG));
- /* No room for a new message, stop the queue until at least one
- * successful transmit
- */
- if (count >= can->can.echo_skb_max || can->can.echo_skb[can->echo_idx])
- netif_stop_queue(netdev);
- spin_unlock_irqrestore(&can->echo_lock, irq_flags);
+ netif_subqueue_maybe_stop(netdev, 0, kvaser_pciefd_tx_avail(can), 1, 1);

return NETDEV_TX_OK;
}
@@ -970,6 +977,8 @@ static int kvaser_pciefd_setup_can_ctrls(struct kvaser_pciefd *pcie)
can->kv_pcie = pcie;
can->cmd_seq = 0;
can->err_rep_cnt = 0;
+ can->completed_tx_pkts = 0;
+ can->completed_tx_bytes = 0;
can->bec.txerr = 0;
can->bec.rxerr = 0;

@@ -983,11 +992,10 @@ static int kvaser_pciefd_setup_can_ctrls(struct kvaser_pciefd *pcie)
tx_nr_packets_max =
FIELD_GET(KVASER_PCIEFD_KCAN_TX_NR_PACKETS_MAX_MASK,
ioread32(can->reg_base + KVASER_PCIEFD_KCAN_TX_NR_PACKETS_REG));
+ can->tx_max_count = min(KVASER_PCIEFD_CAN_TX_MAX_COUNT, tx_nr_packets_max - 1);

can->can.clock.freq = pcie->freq;
- can->can.echo_skb_max = min(KVASER_PCIEFD_CAN_TX_MAX_COUNT, tx_nr_packets_max - 1);
- can->echo_idx = 0;
- spin_lock_init(&can->echo_lock);
+ can->can.echo_skb_max = roundup_pow_of_two(can->tx_max_count);
spin_lock_init(&can->lock);

can->can.bittiming_const = &kvaser_pciefd_bittiming_const;
@@ -1510,19 +1518,21 @@ static int kvaser_pciefd_handle_ack_packet(struct kvaser_pciefd *pcie,
netdev_dbg(can->can.dev, "Packet was flushed\n");
} else {
int echo_idx = FIELD_GET(KVASER_PCIEFD_PACKET_SEQ_MASK, p->header[0]);
- int len;
- u8 count;
+ unsigned int len, frame_len = 0;
struct sk_buff *skb;

+ if (echo_idx != (can->ack_idx & (can->can.echo_skb_max - 1)))
+ return 0;
skb = can->can.echo_skb[echo_idx];
- if (skb)
- kvaser_pciefd_set_skb_timestamp(pcie, skb, p->timestamp);
- len = can_get_echo_skb(can->can.dev, echo_idx, NULL);
- count = FIELD_GET(KVASER_PCIEFD_KCAN_TX_NR_PACKETS_CURRENT_MASK,
- ioread32(can->reg_base + KVASER_PCIEFD_KCAN_TX_NR_PACKETS_REG));
+ if (!skb)
+ return 0;
+ kvaser_pciefd_set_skb_timestamp(pcie, skb, p->timestamp);
+ len = can_get_echo_skb(can->can.dev, echo_idx, &frame_len);

- if (count < can->can.echo_skb_max && netif_queue_stopped(can->can.dev))
- netif_wake_queue(can->can.dev);
+ /* Pairs with barrier in kvaser_pciefd_start_xmit() */
+ smp_store_release(&can->ack_idx, can->ack_idx + 1);
+ can->completed_tx_pkts++;
+ can->completed_tx_bytes += frame_len;

if (!one_shot_fail) {
can->can.dev->stats.tx_bytes += len;
@@ -1638,11 +1646,26 @@ static int kvaser_pciefd_read_buffer(struct kvaser_pciefd *pcie, int dma_buf)
{
int pos = 0;
int res = 0;
+ unsigned int i;

do {
res = kvaser_pciefd_read_packet(pcie, &pos, dma_buf);
} while (!res && pos > 0 && pos < KVASER_PCIEFD_DMA_SIZE);

+ /* Report ACKs in this buffer to BQL en masse for correct periods */
+ for (i = 0; i < pcie->nr_channels; ++i) {
+ struct kvaser_pciefd_can *can = pcie->can[i];
+
+ if (!can->completed_tx_pkts)
+ continue;
+ netif_subqueue_completed_wake(can->can.dev, 0,
+ can->completed_tx_pkts,
+ can->completed_tx_bytes,
+ kvaser_pciefd_tx_avail(can), 1);
+ can->completed_tx_pkts = 0;
+ can->completed_tx_bytes = 0;
+ }
+
return res;
}

--
2.47.2