linux-kernel - Re: [PATCH] usb: core: urb: change a dev_WARN() to dev

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Date:   Mon, 10 Feb 2020 11:04:19 -0800
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        syzbot <syzbot+1bc2c2afd44f820a669f@...kaller.appspotmail.com>,
        andreyknvl@...gle.com, ingrassia@...genesys.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] usb: core: urb: change a dev_WARN() to dev_err() for
 syzbot

On Fri, Jan 31, 2020 at 08:06:52AM +0300, Dan Carpenter wrote:
> We changed this from dev_err() to dev_WARN() in commit 0cb54a3e47cb
> ("USB: debugging code shouldn't alter control flow").
> 
> The difference between dev_WARN() and dev_err() is that dev_WARN()
> prints a stack trace and if you have panic on OOPS enabled then it leads
> to a panic.  The dev_err() function just prints the error message.
> 
> Back in the day we didn't have usb emulators fuzz testing the kernel
> so dev_WARN() didn't cause a problem for anyone, but these days the
> dev_WARN() interferes with syzbot so let's change this to a dev_err().
> 
> Reported-by: syzbot+1bc2c2afd44f820a669f@...kaller.appspotmail.com
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> 
>  drivers/usb/core/urb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
> index da923ec17612..0980c1d2253d 100644
> --- a/drivers/usb/core/urb.c
> +++ b/drivers/usb/core/urb.c
> @@ -475,7 +475,7 @@ int usb_submit_urb(struct urb *urb, gfp_t mem_flags)
>  
>  	/* Check that the pipe's type matches the endpoint's type */
>  	if (usb_urb_ep_type_check(urb))
> -		dev_WARN(&dev->dev, "BOGUS urb xfer, pipe %x != type %x\n",
> +		dev_err(&dev->dev, "BOGUS urb xfer, pipe %x != type %x\n",
>  			usb_pipetype(urb->pipe), pipetypes[xfertype]);

Like others said, we should have the stack trace here.  So can you
change this to dev_warn() and a stacktrace?

thanks,

greg k-h