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

From: Jacob Kroon <jacob.kroon@gmail.com>
To: linux-can@vger.kernel.org
Subject: Re: CM-ITC, pch_can/c_can_pci, sendto() returning ENOBUFS
Date: Mon, 29 Aug 2022 11:14:38 +0200	[thread overview]
Message-ID: <36d0419b-297f-8e39-8843-051b55b8a2bb@gmail.com> (raw)
In-Reply-To: <403e18fe-8695-cd56-38f3-0ffe3ec9e472@gmail.com>

On 8/26/22 13:24, Jacob Kroon wrote:
> 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.
> 

Switching back to the pch_can driver. I'm guessing here but it would 
seem that the driver is not receiving the TX interrupt for 
'PCH_TX_OBJ_END' that would wake up the netif queue, since with the 
changes below I can't reproduce the hang, although I'm still seeing a 
lot of "echo_skb <x> is occupied!":

> diff --git a/drivers/net/can/pch_can.c b/drivers/net/can/pch_can.c
> index 964c8a09226a..75ad2272d9b2 100644
> --- a/drivers/net/can/pch_can.c
> +++ b/drivers/net/can/pch_can.c
> @@ -719,8 +720,7 @@ static void pch_can_tx_complete(struct net_device *ndev, u32 int_stat)
>                           PCH_IF_MCONT_DLC);
>         stats->tx_bytes += dlc;
>         stats->tx_packets++;
> -       if (int_stat == PCH_TX_OBJ_END)
> -               netif_wake_queue(ndev);
> +       netif_wake_queue(ndev);
>  }

Jacob