The following happened on an i.MX25 using flexcan with many packets on the bus:

The rx-offload queue reached a length more than skb_queue_len_max. In can_rx_offload_offload_one() the drop variable was set to true which made the call to .mailbox_read() (here: flexcan_mailbox_read()) to _always_ return ERR_PTR(-ENOBUFS) and drop the rx'ed CAN frame. So can_rx_offload_offload_one() returned ERR_PTR(-ENOBUFS), too.

can_rx_offload_irq_offload_fifo() looks as follows:

| while (1) { | skb = can_rx_offload_offload_one(offload, 0); | if (IS_ERR(skb)) | continue; | if (!skb) | break; | ... | }

The flexcan driver wrongly always returns ERR_PTR(-ENOBUFS) if drop is requested, even if there is no CAN frame pending. As the i.MX25 is a single core CPU, while the rx-offload processing is active, there is no thread to process packets from the offload queue. So the queue doesn't get any shorter and this results is a tight loop.

Instead of always returning ERR_PTR(-ENOBUFS) if drop is requested, return NULL if no CAN frame is pending.

Changes since v1: https://lore.kernel.org/all/20220810144536.389237-1-u.kleine-koenig@pengutro... - don't break in can_rx_offload_irq_offload_fifo() in case of an error, return NULL in flexcan_mailbox_read() in case of no pending CAN frame instead

Fixes: 4e9c9484b085 ("can: rx-offload: Prepare for CAN FD support") Link: https://lore.kernel.org/all/20220811094254.1864367-1-mkl@pengutronix.de Cc: stable@vger.kernel.org # v5.5 Suggested-by: Uwe Kleine-König u.kleine-koenig@pengutronix.de Reviewed-by: Uwe Kleine-König u.kleine-koenig@pengutronix.de Tested-by: Thorsten Scherer t.scherer@eckelmann.de Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- drivers/net/can/flexcan/flexcan-core.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/can/flexcan/flexcan-core.c b/drivers/net/can/flexcan/flexcan-core.c index f857968efed7..ccb438eca517 100644 --- a/drivers/net/can/flexcan/flexcan-core.c +++ b/drivers/net/can/flexcan/flexcan-core.c @@ -941,11 +941,6 @@ static struct sk_buff *flexcan_mailbox_read(struct can_rx_offload *offload, u32 reg_ctrl, reg_id, reg_iflag1; int i;

- if (unlikely(drop)) { - skb = ERR_PTR(-ENOBUFS); - goto mark_as_read; - } - mb = flexcan_get_mb(priv, n);

if (priv->devtype_data.quirks & FLEXCAN_QUIRK_USE_RX_MAILBOX) { @@ -974,6 +969,11 @@ static struct sk_buff *flexcan_mailbox_read(struct can_rx_offload *offload, reg_ctrl = priv->read(&mb->can_ctrl); }

+ if (unlikely(drop)) { + skb = ERR_PTR(-ENOBUFS); + goto mark_as_read; + } + if (reg_ctrl & FLEXCAN_MB_CNT_EDL) skb = alloc_canfd_skb(offload->dev, &cfd); else

base-commit: 6a1dbfefdae4f7809b3e277cc76785dac0ac1cd0