linux-kernel - [PATCH] usb: gadget: Fix spinlock lockup on usb_function

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Date:   Thu,  5 Nov 2020 11:09:30 +0530
From:   Sriharsha Allenki <sallenki@...eaurora.org>
To:     balbi@...nel.org, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        jackp@...eaurora.org, mgautam@...eaurora.org,
        Sriharsha Allenki <sallenki@...eaurora.org>,
        Peter Chen <peter.chen@....com>
Subject: [PATCH] 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_activate.

Reported-by: Peter Chen <peter.chen@....com>
Link: https://lore.kernel.org/linux-usb/20201102094936.GA29581@b29397-desktop/
Tested-by: Peter Chen <peter.chen@....com>
Signed-off-by: Sriharsha Allenki <sallenki@...eaurora.org>
---
 drivers/usb/gadget/composite.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index c6d455f2bb92..1a556a628971 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -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);
-- 
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