Re: CM-ITC, pch_can/c_can_pci, sendto() returning ENOBUFS

[Jacob Kroon <jacob.kroon@gmail.com>]

On 8/25/22 15:25, Jacob Kroon wrote:
> Hi,
> 
> I am using a CM-ITC board 
> (https://www.compulab.com/products/computer-on-modules/cm-itc/) with an 
> application that uses the CAN interface. After a while of successfully 
> sending packets, sendto() starts returning ENOBUFS. I wait a whole 
> second and try to send, several retries, but I get ENOBUFS every time. 
> I'm using kernel 5.15.59, and I've tried both the pch_can and c_can_pci 
> driver, but both show the same error.
> 
> In the console I see several of:
> can0: can_put_echo_skb: BUG! echo_skb 0 is occupied
> 
> I've also tried to increase the txqueuelen to 1000, as suggested here
> 
> https://stackoverflow.com/questions/40424433/write-no-buffer-space-available-socket-can-linux-can 
> 
> 
> but I think that if I increase the queuelen the threads just block 
> forever in sendto() (sockets are opened in blocking mode)
> 
> If I bring down the interface with
> 
> ifconfig can0 down
> ifconfig can0 up
> 
> the transmitting does get unblocked.
> 
> Is there anything I can do to debug this further ? Any other ideas ?
> 

First I get the print:

can_put_echo_skb: BUG! echo_skb 0 is occupied!

then netif_stop_queue() is called from here:

https://github.com/torvalds/linux/blob/master/drivers/net/can/c_can/c_can_main.c#L469

and then there is no call to netif_start_queue(), so the bus hangs.

Jacob