Re: [PATCH] CDC-ACM: fix poison/unpoison imbalance

From: Stefan Agner <stefan@agner.ch>
To: Oliver Neukum <oneukum@suse.com>
Cc: gregKH@linuxfoundation.org, linux-usb@vger.kernel.org
Subject: Re: [PATCH] CDC-ACM: fix poison/unpoison imbalance
Date: Thu, 22 Apr 2021 13:35:30 +0200	[thread overview]
Message-ID: <ffd33d14769dd51375c87d43fff9cc3d@agner.ch> (raw)
In-Reply-To: <20210421074513.4327-1-oneukum@suse.com>

On 2021-04-21 09:45, Oliver Neukum wrote:
> suspend() does its poisoning conditionally, resume() does it
> unconditionally. On a device with combined interfaces this
> will balance, on a device with two interfaces the counter will
> go negative and resubmission will fail.
> 
> Both actions need to be done conditionally.

FWIW, this relates to the issue reported on the kernel bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=212725

Thanks for addressing this!

> 
> Fixes: 6069e3e927c8f ("USB: cdc-acm: untangle a circular dependency
> between callback and softint")
> Signed-off-by: Oliver Neukum <oneukum@suse.com>

Tested-by: Stefan Agner <stefan@agner.ch>

--
Stefan

> ---
>  drivers/usb/class/cdc-acm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index 3fda1ec961d7..f5886c512fec 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -1634,12 +1634,13 @@ static int acm_resume(struct usb_interface *intf)
>  	struct urb *urb;
>  	int rv = 0;
>  
> -	acm_unpoison_urbs(acm);
>  	spin_lock_irq(&acm->write_lock);
>  
>  	if (--acm->susp_count)
>  		goto out;
>  
> +	acm_unpoison_urbs(acm);
> +
>  	if (tty_port_initialized(&acm->port)) {
>  		rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);