patch "usb: gadget: Fix spinlock lockup on usb_function_deactivate" added to usb-linus

This is a note to let you know that I've just added the patch titled

usb: gadget: Fix spinlock lockup on usb_function_deactivate

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 5cc35c224a80aa5a5a539510ef049faf0d6ed181 Mon Sep 17 00:00:00 2001
From: Sriharsha Allenki <[email protected]>
Date: Wed, 2 Dec 2020 18:32:20 +0530
Subject: usb: gadget: Fix spinlock lockup on usb_function_deactivate

There is a spinlock lockup as part of composite_disconnect when it tries to acquire cdev->lock as part of usb_gadget_deactivate. This is because the usb_gadget_deactivate is called from usb_function_deactivate with the same spinlock held.

This would result in the below call stack and leads to stall.

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:

rcu: 3-...0: (1 GPs behind) idle=162/1/0x4000000000000000
softirq=10819/10819 fqs=2356
(detected by 2, t=5252 jiffies, g=20129, q=3770)
Task dump for CPU 3:
task:uvc-gadget_wlhe state:R running task stack: 0 pid: 674 ppid:
636 flags:0x00000202

 Call trace:
  __switch_to+0xc0/0x170
  _raw_spin_lock_irqsave+0x84/0xb0
  composite_disconnect+0x28/0x78
  configfs_composite_disconnect+0x68/0x70
  usb_gadget_disconnect+0x10c/0x128
  usb_gadget_deactivate+0xd4/0x108
  usb_function_deactivate+0x6c/0x80
  uvc_function_disconnect+0x20/0x58
  uvc_v4l2_release+0x30/0x88
  v4l2_release+0xbc/0xf0
  __fput+0x7c/0x230
  ____fput+0x14/0x20
  task_work_run+0x88/0x140
  do_notify_resume+0x240/0x6f0
  work_pending+0x8/0x200

Fix this by doing an unlock on cdev->lock before the usb_gadget_deactivate call from usb_function_deactivate.

The same lockup can happen in the usb_gadget_activate path. Fix that path as well.

---
 drivers/usb/gadget/composite.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

index c6d455f2bb92..1a556a628971 100644
@@ -392,8 +392,11 @@ int usb_function_deactivate(struct usb_function *function)
 
 	spin_lock_irqsave(&cdev->lock, flags);
 
-	if (cdev->deactivations == 0)
+	if (cdev->deactivations == 0) {
+		spin_unlock_irqrestore(&cdev->lock, flags);
 		status = usb_gadget_deactivate(cdev->gadget);
+		spin_lock_irqsave(&cdev->lock, flags);
+	}
 	if (status == 0)
 		cdev->deactivations++;
 

@@ -424,8 +427,11 @@ int usb_function_activate(struct usb_function *function)
 		status = -EINVAL;
 	else {
 		cdev->deactivations--;
-		if (cdev->deactivations == 0)
+		if (cdev->deactivations == 0) {
+			spin_unlock_irqrestore(&cdev->lock, flags);
 			status = usb_gadget_activate(cdev->gadget);
+			spin_lock_irqsave(&cdev->lock, flags);
+		}
 	}
 
 	spin_unlock_irqrestore(&cdev->lock, flags);

2.29.2