linux-kernel - Re: [PATCH v2] usb: cdc-wdm: Fix a sleep-in-atomic-context bug in service_outstanding

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Date:   Tue, 11 Sep 2018 09:49:31 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     gregkh@...uxfoundation.org, johan@...nel.org, bjorn@...k.no,
        mingo@...nel.org, oneukum@...e.com, viro@...iv.linux.org.uk,
        mark.rutland@....com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: cdc-wdm: Fix a sleep-in-atomic-context bug in
 service_outstanding_interrupt()

On 2018-09-01 16:12:10 [+0800], Jia-Ju Bai wrote:
> wdm_in_callback() is a completion handler function for the USB driver.
> So it should not sleep. But it calls service_outstanding_interrupt(), 
> which calls usb_submit_urb() with GFP_KERNEL. 

At which point does wdm_in_callback() invoke
service_outstanding_interrupt()? I don't see it. I see one invocation
from wdm_read() and another from service_interrupt_work().

Also, if that would be the case, then spin_unlock_irq() in an USB
completion handler (which might run in IRQ context with interrupts
disabled) would be wrong.

> To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.
> 
> This bug is found by my static analysis tool DSAC.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
> v2:
>  * Add more description.
> ---
>  drivers/usb/class/cdc-wdm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
> index a0d284ef3f40..632a2bfabc08 100644
> --- a/drivers/usb/class/cdc-wdm.c
> +++ b/drivers/usb/class/cdc-wdm.c
> @@ -458,7 +458,7 @@ static int service_outstanding_interrupt(struct wdm_device *desc)
>  
>  	set_bit(WDM_RESPONDING, &desc->flags);
>  	spin_unlock_irq(&desc->iuspin);
> -	rv = usb_submit_urb(desc->response, GFP_KERNEL);
> +	rv = usb_submit_urb(desc->response, GFP_ATOMIC);
>  	spin_lock_irq(&desc->iuspin);
>  	if (rv) {
>  		dev_err(&desc->intf->dev,

Sebastian