linux-kernel - Re: [PATCH] usb: gadget: file

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Date:	Sun, 3 Oct 2010 11:59:46 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Rahul Ruikar <rahul.ruikar@...il.com>
cc:	David Brownell <dbrownell@...rs.sourceforge.net>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Michal Nazarewicz <m.nazarewicz@...sung.com>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: file_storage: Fix error path

On Sun, 3 Oct 2010, Rahul Ruikar wrote:

> call put_device() when device_register() fails.
> 
> Signed-off-by: Rahul Ruikar <rahul.ruikar@...il.com>
> ---
>  drivers/usb/gadget/file_storage.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c
> index a857b7a..2c94318 100644
> --- a/drivers/usb/gadget/file_storage.c
> +++ b/drivers/usb/gadget/file_storage.c
> @@ -3413,6 +3413,7 @@ static int __ref fsg_bind(struct usb_gadget *gadget)
>  
>  		if ((rc = device_register(&curlun->dev)) != 0) {
>  			INFO(fsg, "failed to register LUN%d: %d\n", i, rc);
> +			put_device(&curlun->dev);
>  			goto out;
>  		}
>  		if ((rc = device_create_file(&curlun->dev,

I'm afraid this is wrong as well.  You need to move the 
"kref_get(&fsg->ref);" line up before the device_register call; 
otherwise the lun_release routine will do an unbalanced kref_put.  In 
fact there is a similar bug in the original code, in the failure path 
for the device_create_file calls.

This seems to be a common pattern of mistakes in your patches.  Maybe
you should go through and check all of them; make sure that everything
the release routine _undoes_ is certain to be _done_ before the
device_register call.

Alan Stern

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