usb: gadget: fix spinlock dead lock in gadgetfs

commit d246dcb2 upstream.

[   40.467381] =============================================
[   40.473013] [ INFO: possible recursive locking detected ]
[   40.478651] 4.6.0-08691-g7f3db9a #37 Not tainted
[   40.483466] ---------------------------------------------
[   40.489098] usb/733 is trying to acquire lock:
[   40.493734]  (&(&dev->lock)->rlock){-.....}, at: [<bf129288>] ep0_complete+0x18/0xdc [gadgetfs]
[   40.502882]
[   40.502882] but task is already holding lock:
[   40.508967]  (&(&dev->lock)->rlock){-.....}, at: [<bf12a420>] ep0_read+0x20/0x5e0 [gadgetfs]
[   40.517811]
[   40.517811] other info that might help us debug this:
[   40.524623]  Possible unsafe locking scenario:
[   40.524623]
[   40.530798]        CPU0
[   40.533346]        ----
[   40.535894]   lock(&(&dev->lock)->rlock);
[   40.540088]   lock(&(&dev->lock)->rlock);
[   40.544284]
[   40.544284]  *** DEADLOCK ***
[   40.544284]
[   40.550461]  May be due to missing lock nesting notation
[   40.550461]
[   40.557544] 2 locks held by usb/733:
[   40.561271]  #0:  (&f->f_pos_lock){+.+.+.}, at: [<c02a6114>] __fdget_pos+0x40/0x48
[   40.569219]  #1:  (&(&dev->lock)->rlock){-.....}, at: [<bf12a420>] ep0_read+0x20/0x5e0 [gadgetfs]
[   40.578523]
[   40.578523] stack backtrace:
[   40.583075] CPU: 0 PID: 733 Comm: usb Not tainted 4.6.0-08691-g7f3db9a #37
[   40.590246] Hardware name: Generic AM33XX (Flattened Device Tree)
[   40.596625] [<c010ffbc>] (unwind_backtrace) from [<c010c1bc>] (show_stack+0x10/0x14)
[   40.604718] [<c010c1bc>] (show_stack) from [<c04207fc>] (dump_stack+0xb0/0xe4)
[   40.612267] [<c04207fc>] (dump_stack) from [<c01886ec>] (__lock_acquire+0xf68/0x1994)
[   40.620440] [<c01886ec>] (__lock_acquire) from [<c0189528>] (lock_acquire+0xd8/0x238)
[   40.628621] [<c0189528>] (lock_acquire) from [<c06ad6b4>] (_raw_spin_lock_irqsave+0x38/0x4c)
[   40.637440] [<c06ad6b4>] (_raw_spin_lock_irqsave) from [<bf129288>] (ep0_complete+0x18/0xdc [gadgetfs])
[   40.647339] [<bf129288>] (ep0_complete [gadgetfs]) from [<bf10a728>] (musb_g_giveback+0x118/0x1b0 [musb_hdrc])
[   40.657842] [<bf10a728>] (musb_g_giveback [musb_hdrc]) from [<bf108768>] (musb_g_ep0_queue+0x16c/0x188 [musb_hdrc])
[   40.668772] [<bf108768>] (musb_g_ep0_queue [musb_hdrc]) from [<bf12a944>] (ep0_read+0x544/0x5e0 [gadgetfs])
[   40.678963] [<bf12a944>] (ep0_read [gadgetfs]) from [<c0284470>] (__vfs_read+0x20/0x110)
[   40.687414] [<c0284470>] (__vfs_read) from [<c0285324>] (vfs_read+0x88/0x114)
[   40.694864] [<c0285324>] (vfs_read) from [<c0286150>] (SyS_read+0x44/0x9c)
[   40.702051] [<c0286150>] (SyS_read) from [<c0107820>] (ret_fast_syscall+0x0/0x1c)

This is caused by the spinlock bug in ep0_read().
Fix the two other deadlock sources in gadgetfs_setup() too.
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/gadget/inode.c

@@ -1010,8 +1010,11 @@ ep0_read (struct file *fd, char __user *buf, size_t len, loff_t *ptr)
 			struct usb_ep		*ep = dev->gadget->ep0;
 			struct usb_request	*req = dev->req;
 
-			if ((retval = setup_req (ep, req, 0)) == 0)
-				retval = usb_ep_queue (ep, req, GFP_ATOMIC);
+			if ((retval = setup_req (ep, req, 0)) == 0) {
+				spin_unlock_irq (&dev->lock);
+				retval = usb_ep_queue (ep, req, GFP_KERNEL);
+				spin_lock_irq (&dev->lock);
+			}
 			dev->state = STATE_DEV_CONNECTED;
 
 			/* assume that was SET_CONFIGURATION */
@@ -1542,8 +1545,11 @@ gadgetfs_setup (struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 							w_length);
 				if (value < 0)
 					break;
+
+				spin_unlock (&dev->lock);
 				value = usb_ep_queue (gadget->ep0, dev->req,
-							GFP_ATOMIC);
+							GFP_KERNEL);
+				spin_lock (&dev->lock);
 				if (value < 0) {
 					clean_req (gadget->ep0, dev->req);
 					break;
@@ -1566,11 +1572,14 @@ gadgetfs_setup (struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 	if (value >= 0 && dev->state != STATE_DEV_SETUP) {
 		req->length = value;
 		req->zero = value < w_length;
-		value = usb_ep_queue (gadget->ep0, req, GFP_ATOMIC);
+
+		spin_unlock (&dev->lock);
+		value = usb_ep_queue (gadget->ep0, req, GFP_KERNEL);
 		if (value < 0) {
 			DBG (dev, "ep_queue --> %d\n", value);
 			req->status = 0;
 		}
+		return value;
 	}
 
 	/* device stalls when value < 0 */