From d3104d983465e23fb059cd32d34e8e35a8860fd2 Mon Sep 17 00:00:00 2001
From: Ajay Kaher <ajay.kaher@samsung.com>
Date: Tue, 28 Mar 2017 08:09:32 -0400
Subject: [PATCH] USB: Proper handling of Race Condition when two USB class
 drivers try to call init_usb_class simultaneously

commit 2f86a96be0ccb1302b7eee7855dbee5ce4dc5dfb upstream.

There is race condition when two USB class drivers try to call
init_usb_class at the same time and leads to crash.
code path: probe->usb_register_dev->init_usb_class

To solve this, mutex locking has been added in init_usb_class() and
destroy_usb_class().

As pointed by Alan, removed "if (usb_class)" test from destroy_usb_class()
because usb_class can never be NULL there.

Signed-off-by: Ajay Kaher <ajay.kaher@samsung.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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