linux-kernel - Re: [PATCH] media: imon: ratelimit usb_rx_callback

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Message-ID: <aHAbfmpBWzVVT1r8@gofer.mess.org>
Date: Thu, 10 Jul 2025 20:58:54 +0100
From: Sean Young <sean@...s.org>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: imon: ratelimit usb_rx_callback_intf{0,1} error
 messages

Hello Tetsuo,

Thank you for submitting your patch.

On Thu, Jul 10, 2025 at 10:43:56AM +0900, Tetsuo Handa wrote:
> Ratelimiting flood of
> 
>   imon 1-1:0.0: imon usb_rx_callback_intf0: status(-71): ignored
> 
> message helps reducing possibility of hitting
> 
>   rcu: INFO: rcu_preempt self-detected stall on CPU
>   rcu: 	0-....: (10485 ticks this GP) idle=ff54/1/0x4000000000000000 softirq=53201/53201 fqs=5246
>   rcu: 	         hardirqs   softirqs   csw/system
>   rcu: 	 number:     6548       7856            0
>   rcu: 	cputime:        0        739        51598   ==> 52490(ms)
>   rcu: 	(t=10500 jiffies g=34137 q=35661 ncpus=2)
>   CPU: 0 UID: 0 PID: 6858 Comm: kworker/0:4 Not tainted 6.16.0-rc4-syzkaller-00300-g81c3b7256f9e #0 PREEMPT(voluntary)
>   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
>   Workqueue: usb_hub_wq hub_event
>   RIP: 0010:console_flush_all+0x9a2/0xc60 kernel/printk/printk.c:3227
> 
> messages.
> 
> Link: https://syzkaller.appspot.com/bug?extid=592e2ab8775dbe0bf09a
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
>  drivers/media/rc/imon.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
> index f5221b018808..10124a26ffde 100644
> --- a/drivers/media/rc/imon.c
> +++ b/drivers/media/rc/imon.c
> @@ -1765,7 +1765,7 @@ static void usb_rx_callback_intf0(struct urb *urb)
>  		break;
>  
>  	default:
> -		dev_warn(ictx->dev, "imon %s: status(%d): ignored\n",
> +		dev_warn_ratelimited(ictx->dev, "imon %s: status(%d): ignored\n",

>  			 __func__, urb->status);

I'm not sure this is the right way to go about this. When the usb callback
receives urb status -71 (-EPROTO, i.e. protocol error or unplug), then there
is no use in continuing to resubmit the urb; you will only get more failures
like you are seeing here.

So I think for -EPROTO, simply return and do not resubmit the urb. TBH
I am not sure if usb_unlink_urb() is required in this case, that needs
investigation.

>  		break;
>  	}
> @@ -1806,7 +1806,7 @@ static void usb_rx_callback_intf1(struct urb *urb)
>  		break;
>  
>  	default:
> -		dev_warn(ictx->dev, "imon %s: status(%d): ignored\n",
> +		dev_warn_ratelimited(ictx->dev, "imon %s: status(%d): ignored\n",
>  			 __func__, urb->status);

Same here.

>  		break;
>  	}
> -- 
> 2.47.1
>