linux-kernel - Re: [PATCH] usb: gadget: composite: split spinlock to avoid recursion

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Message-ID: <20191113063414.GA30608@b29397-desktop>
Date:   Wed, 13 Nov 2019 06:31:55 +0000
From:   Peter Chen <peter.chen@....com>
To:     Michael Olbrich <m.olbrich@...gutronix.de>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: composite: split spinlock to avoid recursion

On 19-11-12 10:33:18, Michael Olbrich wrote:
> 'delayed_status' and 'deactivations' are used completely independent but
> they share the same spinlock. This can result in spinlock recursion:
> 
> BUG: spinlock recursion on CPU#1, uvc-gadget/322
>  lock: 0xffffffc0570364e0, .magic: dead4ead, .owner: uvc-gadget/322, .owner_cpu: 1
> CPU: 1 PID: 322 Comm: uvc-gadget Tainted: G         C O      5.3.0-20190916-1+ #55
> Hardware name: XXXXX (DT)
> Call trace:
>  dump_backtrace+0x0/0x178
>  show_stack+0x24/0x30
>  dump_stack+0xc0/0x104
>  spin_dump+0x90/0xa0
>  do_raw_spin_lock+0xd8/0x108
>  _raw_spin_lock_irqsave+0x40/0x50
>  composite_disconnect+0x2c/0x80
>  usb_gadget_disconnect+0x84/0x150
>  usb_gadget_deactivate+0x64/0x120
>  usb_function_deactivate+0x70/0x80
>  uvc_function_disconnect+0x20/0x58
>  uvc_v4l2_release+0x34/0x90
>  v4l2_release+0xbc/0xf0
>  __fput+0xb0/0x218
>  ____fput+0x20/0x30
>  task_work_run+0xa0/0xd0
>  do_notify_resume+0x2f4/0x340
>  work_pending+0x8/0x14
> 
> Fix this by using separate spinlocks.

This issue may be introduced by 0a55187a1ec8c ("USB: gadget core: Issue
->disconnect() callback from usb_gadget_disconnect()"), which adds
gadget's disconnect at usb_gadget_disconnect. Add Alan, if he is Ok
with your patch, you may cc to stable tree.

> 
> Signed-off-by: Michael Olbrich <m.olbrich@...gutronix.de>
> ---
>  drivers/usb/gadget/composite.c | 9 +++++----
>  drivers/usb/gadget/configfs.c  | 1 +
>  include/linux/usb/composite.h  | 4 +++-
>  3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> index 76883ff4f5bb..35c792e5b408 100644
> --- a/drivers/usb/gadget/composite.c
> +++ b/drivers/usb/gadget/composite.c
> @@ -346,14 +346,14 @@ int usb_function_deactivate(struct usb_function *function)
>  	unsigned long			flags;
>  	int				status = 0;
>  
> -	spin_lock_irqsave(&cdev->lock, flags);
> +	spin_lock_irqsave(&cdev->deactivations_lock, flags);
>  
>  	if (cdev->deactivations == 0)
>  		status = usb_gadget_deactivate(cdev->gadget);
>  	if (status == 0)
>  		cdev->deactivations++;
>  
> -	spin_unlock_irqrestore(&cdev->lock, flags);
> +	spin_unlock_irqrestore(&cdev->deactivations_lock, flags);
>  	return status;
>  }
>  EXPORT_SYMBOL_GPL(usb_function_deactivate);
> @@ -374,7 +374,7 @@ int usb_function_activate(struct usb_function *function)
>  	unsigned long			flags;
>  	int				status = 0;
>  
> -	spin_lock_irqsave(&cdev->lock, flags);
> +	spin_lock_irqsave(&cdev->deactivations_lock, flags);
>  
>  	if (WARN_ON(cdev->deactivations == 0))
>  		status = -EINVAL;
> @@ -384,7 +384,7 @@ int usb_function_activate(struct usb_function *function)
>  			status = usb_gadget_activate(cdev->gadget);
>  	}
>  
> -	spin_unlock_irqrestore(&cdev->lock, flags);
> +	spin_unlock_irqrestore(&cdev->deactivations_lock, flags);
>  	return status;
>  }
>  EXPORT_SYMBOL_GPL(usb_function_activate);
> @@ -2196,6 +2196,7 @@ static int composite_bind(struct usb_gadget *gadget,
>  		return status;
>  
>  	spin_lock_init(&cdev->lock);
> +	spin_lock_init(&cdev->deactivations_lock);
>  	cdev->gadget = gadget;
>  	set_gadget_data(gadget, cdev);
>  	INIT_LIST_HEAD(&cdev->configs);
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index 025129942894..45f717fcdb89 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -521,6 +521,7 @@ static const struct config_item_type gadget_root_type = {
>  static void composite_init_dev(struct usb_composite_dev *cdev)
>  {
>  	spin_lock_init(&cdev->lock);
> +	spin_lock_init(&cdev->deactivations_lock);
>  	INIT_LIST_HEAD(&cdev->configs);
>  	INIT_LIST_HEAD(&cdev->gstrings);
>  }
> diff --git a/include/linux/usb/composite.h b/include/linux/usb/composite.h
> index 8675e145ea8b..86eb6f2c03ac 100644
> --- a/include/linux/usb/composite.h
> +++ b/include/linux/usb/composite.h
> @@ -505,8 +505,10 @@ struct usb_composite_dev {
>  	 */
>  	int				delayed_status;
>  
> -	/* protects deactivations and delayed_status counts*/
> +	/* protects delayed_status counts*/
>  	spinlock_t			lock;

In fact, this lock is used many places, not only at setup delayed cases.
You may change comments or delete the comments.

> +	/* protects deactivations counts*/

Add one space after 'counts'.

> +	spinlock_t			deactivations_lock;
>  

-- 

Thanks,
Peter Chen