4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Clemens Gruber <clemens.gru...@pqgruber.com>

commit 6f3c4fb6d05e63c9c6d8968302491c3a5457be61 upstream.

Problems with the signal integrity of the high speed USB data lines or
noise on reference ground lines can cause the i.MX6 USB controller to
violate USB specs and exhibit unexpected behavior.

It was observed that USBi_UI interrupts were triggered first and when
isr_setup_status_phase was called, ci->status was NULL, which lead to a
NULL pointer dereference kernel panic.

This patch fixes the kernel panic, emits a warning once and returns
-EPIPE to halt the device and let the host get stalled.
It also adds a comment to point people, who are experiencing this issue,
to their USB hardware design.

Signed-off-by: Clemens Gruber <clemens.gru...@pqgruber.com>
Signed-off-by: Peter Chen <peter.c...@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/usb/chipidea/udc.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/usb/chipidea/udc.c
+++ b/drivers/usb/chipidea/udc.c
@@ -939,6 +939,15 @@ static int isr_setup_status_phase(struct
        int retval;
        struct ci_hw_ep *hwep;
 
+       /*
+        * Unexpected USB controller behavior, caused by bad signal integrity
+        * or ground reference problems, can lead to isr_setup_status_phase
+        * being called with ci->status equal to NULL.
+        * If this situation occurs, you should review your USB hardware design.
+        */
+       if (WARN_ON_ONCE(!ci->status))
+               return -EPIPE;
+
        hwep = (ci->ep0_dir == TX) ? ci->ep0out : ci->ep0in;
        ci->status->context = ci;
        ci->status->complete = isr_setup_status_complete;


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