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Subject[PATCH v2] usb: gadget: Fix spinlock lockup on usb_function_deactivate
Date
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.

Reported-by: Peter Chen <peter.chen@nxp.com>
Link: https://lore.kernel.org/linux-usb/20201102094936.GA29581@b29397-desktop/
Tested-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>
---
Changes since v1:
- Updated commit text to reflect fix in usb_gadget_activate as well

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);
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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