usb: gadget: check for accessory device before disconnecting HIDs

While disabling ConfigFS Android gadget, android_disconnect() calls
kill_all_hid_devices(), if CONFIG_USB_CONFIGFS_F_ACC is enabled, to free
the registered HIDs without checking whether the USB accessory device
really exist or not. If USB accessory device doesn't exist then we run into
following kernel panic:
----8<----
[  136.724761] Unable to handle kernel NULL pointer dereference at virtual address 00000064
[  136.724809] pgd = c0204000
[  136.731924] [00000064] *pgd=00000000
[  136.737830] Internal error: Oops: 5 [#1] SMP ARM
[  136.738108] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.0-rc4-00400-gf75300e-dirty #76
[  136.742788] task: c0fb19d8 ti: c0fa4000 task.ti: c0fa4000
[  136.750890] PC is at _raw_spin_lock_irqsave+0x24/0x60
[  136.756246] LR is at kill_all_hid_devices+0x24/0x114
---->8----

This patch adds a test to check if USB Accessory device exists before freeing HIDs.

Change-Id: Ie229feaf0de3f4f7a151fcaa9a994e34e15ff73b
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>

diff --git a/drivers/usb/gadget/f_accessory.c b/drivers/usb/gadget/f_accessory.c
index f8490c034107eabce7ac7f3d4f01de7cf23fa3df..9ffe017bf1cf3a67030235b61b70f83d6345e526 100644 (file)
--- a/drivers/usb/gadget/f_accessory.c
+++ b/drivers/usb/gadget/f_accessory.c
@@ -929,6 +929,10 @@ kill_all_hid_devices(struct acc_dev *dev)
        struct list_head *entry, *temp;
        unsigned long flags;
 
+       /* do nothing if usb accessory device doesn't exist */
+       if (!dev)
+               return;
+
        spin_lock_irqsave(&dev->lock, flags);
        list_for_each_safe(entry, temp, &dev->hid_list) {
                hid = list_entry(entry, struct acc_hid_dev, list);