linux-kernel - Re: [PATCH v4] USB: Proper handling of Race Condition when two USB class drivers try to call init_usb

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Date:   Thu, 23 Mar 2017 08:18:50 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Ajay Kaher <ajay.kaher@...sung.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        AMAN DEEP <aman.deep@...sung.com>,
        HEMANSHU SRIVASTAVA <hemanshu.s@...sung.com>
Subject: Re: [PATCH v4] USB: Proper handling of Race Condition when two USB
 class drivers try to call init_usb_class simultaneously

On Fri, Mar 17, 2017 at 10:56:37AM +0000, Ajay Kaher wrote:
> There is race condition when two USB class drivers try to call
> init_usb_class at the same time and leads to crash.
> code path: probe->usb_register_dev->init_usb_class
> 
> To solve this, mutex locking has been added in init_usb_class() and 
> destroy_usb_class().
> 
> As pointed by Alan, removed "if (usb_class)" test from destroy_usb_class()
> because usb_class can never be NULL there.
> 
> Signed-off-by: Ajay Kaher <ajay.kaher@...sung.com>
> Acked-by: Alan Stern <stern@...land.harvard.edu>
> ---
>  drivers/usb/core/file.c |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c
> index 822ced9..422ce7b 100644
> --- a/drivers/usb/core/file.c
> +++ b/drivers/usb/core/file.c
> @@ -27,6 +27,7 @@
>  #define MAX_USB_MINORS	256
>  static const struct file_operations *usb_minors[MAX_USB_MINORS];
>  static DECLARE_RWSEM(minor_rwsem);
> +static DEFINE_MUTEX(init_usb_class_mutex);
>  
>  static int usb_open(struct inode *inode, struct file *file)
>  {
> @@ -109,8 +110,9 @@ static void release_usb_class(struct kref *kref)
>  
>  static void destroy_usb_class(void)
>  {
> -	if (usb_class)
> -		kref_put(&usb_class->kref, release_usb_class);
> +	mutex_lock(&init_usb_class_mutex);
> +	kref_put(&usb_class->kref, release_usb_class);
> +	mutex_unlock(&init_usb_class_mutex);
>  }
>  
>  int usb_major_init(void)
> @@ -171,7 +173,10 @@ int usb_register_dev(struct usb_interface *intf,
>  	if (intf->minor >= 0)
>  		return -EADDRINUSE;
>  
> +	mutex_lock(&init_usb_class_mutex);
>  	retval = init_usb_class();
> +	mutex_unlock(&init_usb_class_mutex);
> +
>  	if (retval)
>  		return retval;
>  

I get the following errors when trying to apply this patch:

Applying: USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously
.git/rebase-apply/patch:13: trailing whitespace.
static DEFINE_MUTEX(init_usb_class_mutex);
.git/rebase-apply/patch:23: trailing whitespace.
        mutex_lock(&init_usb_class_mutex);
.git/rebase-apply/patch:24: trailing whitespace.
        kref_put(&usb_class->kref, release_usb_class);
.git/rebase-apply/patch:25: trailing whitespace.
        mutex_unlock(&init_usb_class_mutex);
.git/rebase-apply/patch:33: trailing whitespace.
        mutex_lock(&init_usb_class_mutex);
error: patch failed: drivers/usb/core/file.c:27
error: drivers/usb/core/file.c: patch does not apply
Patch failed at 0001 USB: Proper handling of Race Condition when two USB class drivers try to call init_usb_class simultaneously


Are you sure you made this in the correct format?  Seems that the patch
has dos line-ends :(

Please fix up and resend.

thanks,

greg k-h