linux-kernel - Re: [PATCH] usb: yurex: Rearrange code not to need GFP

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Date:   Mon, 21 Sep 2020 14:24:52 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Pavel Machek <pavel@...x.de>, gregkh@...uxfoundation.org,
        stern@...land.harvard.edu, johan@...nel.org, gustavoars@...nel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: yurex: Rearrange code not to need GFP_ATOMIC

Am Sonntag, den 20.09.2020, 10:44 +0200 schrieb Pavel Machek:
> Move prepare to wait around, so that normal GFP_KERNEL allocation can
> be used.
> 
> Signed-off-by: Pavel Machek (CIP) <pavel@...x.de>
> Acked-by: Alan Stern <stern@...land.harvard.edu>

Ehm. Please recheck.

> diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
> index b2e09883c7e2..071f1debebba 100644
> --- a/drivers/usb/misc/yurex.c
> +++ b/drivers/usb/misc/yurex.c
> @@ -489,10 +489,10 @@ static ssize_t yurex_write(struct file *file, const char __user *user_buffer,
>  	}
>  
>  	/* send the data as the control msg */
> -	prepare_to_wait(&dev->waitq, &wait, TASK_INTERRUPTIBLE);
>  	dev_dbg(&dev->interface->dev, "%s - submit %c\n", __func__,
>  		dev->cntl_buffer[0]);
> -	retval = usb_submit_urb(dev->cntl_urb, GFP_ATOMIC);
> +	retval = usb_submit_urb(dev->cntl_urb, GFP_KERNEL);

URB completes here. wake_up() returns the task to RUNNING.

> +	prepare_to_wait(&dev->waitq, &wait, TASK_INTERRUPTIBLE);

Task goes to TASK_INTERRUPTIBLE

>  	if (retval >= 0)
>  		timeout = schedule_timeout(YUREX_WRITE_TIMEOUT);

Task turns into Sleeping Beauty until timeout

>  	finish_wait(&dev->waitq, &wait);

And here task goes into error reporting as it checks timeout.

	Regards
		Oliver