linux-kernel - Re: [RFC PATCH] usb: host: xhci: allow __GFP

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Date:   Mon, 20 May 2019 11:09:25 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Jaewon Kim <jaewon31.kim@...il.com>
Cc:     linux-mm@...ck.org, gregkh@...uxfoundation.org,
        Jaewon Kim <jaewon31.kim@...sung.com>,
        m.szyprowski@...sung.com, ytk.lee@...sung.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation

On So, 2019-05-19 at 22:56 -0700, Christoph Hellwig wrote:
> Folks, you can't just pass arbitary GFP_ flags to dma allocation
> routines, beause very often they are not just wrappers around
> the page allocator.
> 
> So no, you can't just fine grained control the flags, but the
> existing code is just as buggy.
> 
> Please switch to use memalloc_noio_save() instead.
> 

Hi,

we actually do. It is just higher up in the calling path:

int usb_reset_device(struct usb_device *udev)
{
        int ret;
        int i;
        unsigned int noio_flag;
        struct usb_port *port_dev;
        struct usb_host_config *config = udev->actconfig;
        struct usb_hub *hub = usb_hub_to_struct_hub(udev->parent);

        if (udev->state == USB_STATE_NOTATTACHED ||
                        udev->state == USB_STATE_SUSPENDED) {
                dev_dbg(&udev->dev, "device reset not allowed in state %d\n",
                                udev->state);
                return -EINVAL;
        }

        if (!udev->parent) {
                /* this requires hcd-specific logic; see ohci_restart() */
                dev_dbg(&udev->dev, "%s for root hub!\n", __func__);
                return -EISDIR;
        }

        port_dev = hub->ports[udev->portnum - 1];

        /*
         * 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 easist
         * approach is to do it for every device reset,
         * because the device 'memalloc_noio' flag may have
         * not been set before reseting the usb device.
         */
        noio_flag = memalloc_noio_save();

So, do we need to audit the mem_flags again?
What are we supposed to use? GFP_KERNEL?

	Regards
		Oliver