linux-kernel - Re: [PATCH] usb: u132-hcd: fix potential NULL pointer dereference

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Message-ID: <20190319135609.GA16254@kroah.com>
Date:   Tue, 19 Mar 2019 14:56:09 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Kangjie Lu <kjlu@....edu>
Cc:     pakki001@....edu, Colin Ian King <colin.king@...onical.com>,
        Jia-Ju Bai <baijiaju1990@...il.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: u132-hcd: fix potential NULL pointer dereference

On Thu, Mar 14, 2019 at 02:27:11AM -0500, Kangjie Lu wrote:
> In case create_singlethread_workqueue fails, the fix notifies
> callers the error to avoid potential NULL pointer dereferences.
> 
> Signed-off-by: Kangjie Lu <kjlu@....edu>
> ---
>  drivers/usb/host/u132-hcd.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/host/u132-hcd.c b/drivers/usb/host/u132-hcd.c
> index 934584f0a20a..6d5b532b03f8 100644
> --- a/drivers/usb/host/u132-hcd.c
> +++ b/drivers/usb/host/u132-hcd.c
> @@ -3203,6 +3203,8 @@ static int __init u132_hcd_init(void)
>  		return -ENODEV;
>  	printk(KERN_INFO "driver %s\n", hcd_name);
>  	workqueue = create_singlethread_workqueue("u132");
> +	if (unlikely(!workqueue))

You only ever use unlikely/likely if you can actually measure the
difference with and without it.  For stuff like this, it is not needed
at all, and in fact, the compiler and CPU already know this type of
thing, so it is going to be faster without it.

And are you sure you properly unwound from anything that was
created/initialized above these lines?

thanks,

greg k-h