Re: strange call stack when running uvc-gadget application

[Sriharsha Allenki <sallenki@codeaurora.org>]

Hi Peter,

On 11/2/2020 3:20 PM, Peter Chen wrote:
> Hi all,
>
> When running run uvc-gadget application at HS using dwc3 gadget at Linux
> v5.10-rc1, the video stream will be stopped after 1-2 minutes running. The
> trace log like below, I wonder how _raw_spin_lock_irqsave calls __switch_to?
> Any hints? Thanks.
>
> usb_test# [ 4757.322728] configfs-gadget gadget: uvc: VS request completed with status -18.
> [ 4757.329971] configfs-gadget gadget: uvc: VS request completed with status -18.
> UVC: Possible USB shutdown requested from Host, seen during VIDIOC_DQBUF
>
> usb_test# [ 4812.376465] check_interval: 37 callbacks suppressed
> [ 4825.307665] configfs-gadget gadget: uvc: VS request completed with status -18.
> [ 4825.314912] configfs-gadget gadget: uvc: VS request completed with status -18.
> UVC: Possible USB shutdown requested from Host, seen during VIDIOC_DQBUF
> [ 4826.231392] check_interval: 3 callbacks suppressed
> select timeout
> [ 4827.336088] dwc3 38100000.dwc3: request 0000000080ebefd3 was not queued to ep2in
> [ 4827.343547] dwc3 38100000.dwc3: request 00000000b578605c was not queued to ep2in
> [ 4827.350989] dwc3 38100000.dwc3: request 00000000c6d191cd was not queued to ep2in
> [ 4827.358422] dwc3 38100000.dwc3: request 0000000085205409 was not queued to ep2in
> UVC: Stopping video stream.
>
> [ 4848.381718] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 4848.387824] rcu:     3-...0: (1 GPs behind) idle=162/1/0x4000000000000000 softirq=10819/10819 fqs=2356
> [ 4848.396956]  (detected by 2, t=5252 jiffies, g=20129, q=3770)
> [ 4848.396959] Task dump for CPU 3:
> [ 4848.405925] task:uvc-gadget_wlhe state:R  running task     stack:    0 pid:  674 ppid:   636 flags:0x00000202
> [ 4848.415842] Call trace:
> [ 4848.418294]  __switch_to+0xc0/0x170
> [ 4848.421785]  _raw_spin_lock_irqsave+0x84/0xb0
> [ 4848.426143]  composite_disconnect+0x28/0x78
> [ 4848.430327]  configfs_composite_disconnect+0x68/0x70
> [ 4848.435290]  usb_gadget_disconnect+0x10c/0x128
> [ 4848.439733]  usb_gadget_deactivate+0xd4/0x108
> [ 4848.444089]  usb_function_deactivate+0x6c/0x80
> [ 4848.448534]  uvc_function_disconnect+0x20/0x58
> [ 4848.452976]  uvc_v4l2_release+0x30/0x88
> [ 4848.456812]  v4l2_release+0xbc/0xf0
> [ 4848.460301]  __fput+0x7c/0x230
> [ 4848.463353]  ____fput+0x14/0x20
> [ 4848.466495]  task_work_run+0x88/0x140
> [ 4848.470157]  do_notify_resume+0x240/0x6f0
> [ 4848.474166]  work_pending+0x8/0x200
The reason for this seems to be that the usb_gadget_deactivate is being called with
spinlock held from the usb_function_deactivate and the same lock is being used
in the composite_disconnect (&cdev->lock).

This should be able to resolve it.

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 05b176c82cc5..5fced737e4ef 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);

This should also protect the cdev->deactivations as well which was the
primary reason for the spinlock here. Hope this helps.

Regards,
Sriharsha
>
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