[1/3] usb: host: xhci: fix oops when removing hcd

[Jack Pham <jackp@codeaurora.org>]

Hi Peter,

On Fri, Sep 21, 2018 at 09:48:43AM +0800, Peter Chen wrote:
> Type-C-to-A cable, and the USB3 HCD has already been NULL at that time.
> The oops log like below:
> 
> [681.782288] xhci-hcd xhci-hcd.1.auto: remove, state 1
> [681.787490] usb usb4: USB disconnect, device number 1
> [681.792808] usb 4-1: USB disconnect, device number 2
> [681.818089] xhci-hcd xhci-hcd.1.auto: USB bus 4 deregistered
> [681.823803] Unable to handle kernel NULL pointer dereference at virtual address 000000a0
> [681.823806] Mem abort info:
> [681.823809]   Exception class = DABT (current EL), IL = 32 bits
> [681.823811]   SET = 0, FnV = 0
> [681.823813]   EA = 0, S1PTW = 0
> [681.823814] Data abort info:
> [681.823816]   ISV = 0, ISS = 0x00000004
> [681.823818]   CM = 0, WnR = 0
> [681.823822] user pgtable: 4k pages, 48-bit VAs, pgd = ffff8000ae3fd000
> [681.823824] [00000000000000a0] *pgd=0000000000000000
> [681.823829] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [681.823832] Modules linked in: 8021q garp stp mrp crc32_ce qca6174(O) crct10dif_ce galcore(O)
> [681.823849] CPU: 0 PID: 94 Comm: kworker/0:1 Tainted: G           O    4.14.62-imx_4.14.y+gcd63def #1
> [681.823851] Hardware name: Freescale i.MX8MQ EVK (DT)
> [681.823862] Workqueue: events_freezable __dwc3_set_mode
> [681.823865] task: ffff8000b8a18000 task.stack: ffff00000a010000
> [681.823872] PC is at xhci_irq+0x5fc/0x14b8
> [681.823875] LR is at xhci_irq+0x3c/0x14b8

<snip>

> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index f0a99aa0ac58..2dc5176b79d0 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -2680,7 +2680,8 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd)
>  	}
>  
>  	if (xhci->xhc_state & XHCI_STATE_DYING ||
> -	    xhci->xhc_state & XHCI_STATE_HALTED) {
> +	    xhci->xhc_state & XHCI_STATE_HALTED ||
> +	    xhci->xhc_state & XHCI_STATE_REMOVING) {
>  		xhci_dbg(xhci, "xHCI dying, ignoring interrupt. "
>  				"Shouldn't IRQs be disabled?\n");
>  		/* Clear the event handler busy flag (RW1C);

We also noticed the same crash as you found, and tried to fix it in a
similar way, but noticed that this still allows a memory leak to happen.

It seems from commit fe190ed0d602a ("xhci: Do not halt the host until
both HCD have disconnected their devices.") this was added to
xhci_stop(), and is the reason we encounter the NULL pointer in
xhci_irq() when it tries to access xhci->shared_hcd.

	+       /* Only halt host and free memory after both hcds are removed */
		if (!usb_hcd_is_primary_hcd(hcd)) {
	+               /* usb core will free this hcd shortly, unset pointer */
	+               xhci->shared_hcd = NULL;
			mutex_unlock(&xhci->mutex);
			return;
		}

While your fix will simply abort the xhci_irq() function if it
encounters XHCI_STATE_REMOVING, during xhci_plat_remove():

	static int xhci_plat_remove(struct platform_device *dev)
	{
		struct usb_hcd  *hcd = platform_get_drvdata(dev);
		struct xhci_hcd *xhci = hcd_to_xhci(hcd);
		struct clk *clk = xhci->clk;
		struct clk *reg_clk = xhci->reg_clk;

		xhci->xhc_state |= XHCI_STATE_REMOVING;

		usb_remove_hcd(xhci->shared_hcd);
		^^^^^^^^^ calls xhci_stop() and sets shared_hcd=NULL
		usb_phy_shutdown(hcd->usb_phy);

		usb_remove_hcd(hcd);
		usb_put_hcd(xhci->shared_hcd);
		^^^^^^^^^^^ shared_hcd==NULL, so this is a no-op

Since usb_put_hcd() doesn't get called for shared_hcd, we end up
with one additional kref count and hence a leak.

Wondering if we need to also remove the xhci->shared_hcd = NULL from
xhci_stop(), in addition to your patches. Thoughts?

Thanks,
Jack