Re: [RFC PATCH v2 6/6] USB: forbid memory allocation with I/O during bus reset

[Alan Stern <stern@rowland.harvard.edu>]

On Mon, 22 Oct 2012, Ming Lei wrote:

> If one storage interface or usb network interface(iSCSI case)
> exists in current configuration, memory allocation with
> GFP_KERNEL during usb_device_reset() might trigger I/O transfer
> on the storage interface itself and cause deadlock because
> the 'us->dev_mutex' is held in .pre_reset() and the storage
> interface can't do I/O transfer when the reset is triggered
> by other interface, or the error handling can't be completed
> if the reset is triggered by the storage itself(error handling path).
> 
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: Oliver Neukum <oneukum@suse.de>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
> ---
>  drivers/usb/core/hub.c |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 522ad57..106a80a 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -5038,6 +5038,7 @@ int usb_reset_device(struct usb_device *udev)
>  {
>  	int ret;
>  	int i;
> +	unsigned int noio_flag;
>  	struct usb_host_config *config = udev->actconfig;
>  
>  	if (udev->state == USB_STATE_NOTATTACHED ||
> @@ -5047,6 +5048,15 @@ int usb_reset_device(struct usb_device *udev)
>  		return -EINVAL;
>  	}
>  
> +	/*
> +	 * Don't allocate memory with GFP_KERNEL in current
> +	 * context to avoid possible deadlock if usb mass
> +	 * storage interface or usbnet interface(iSCSI case)
> +	 * is included in current configuration. The easiest
> +	 * approach is to do it for all devices.
> +	 */
> +	memalloc_noio_save(noio_flag);

Why not check dev->power.memalloc_noio_resume here too?

Alan Stern

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