linux-kernel - Re: [PATCH] usb: misc: chaoskey: get lock before calling usb_[disable|enable]

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Date:   Mon, 2 Aug 2021 20:58:34 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Salah Triki <salah.triki@...il.com>
Cc:     Keith Packard <keithp@...thp.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: misc: chaoskey: get lock before calling
 usb_[disable|enable]_autosuspend()

On Mon, Aug 02, 2021 at 11:22:05PM +0100, Salah Triki wrote:
> Based on the documentation of usb_[disable|enable]_autosuspend(), the
> caller must hold udev's device lock.
> 
> Signed-off-by: Salah Triki <salah.triki@...il.com>
> ---
>  drivers/usb/misc/chaoskey.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/misc/chaoskey.c b/drivers/usb/misc/chaoskey.c
> index 87067c3d6109..8af00be7b9e8 100644
> --- a/drivers/usb/misc/chaoskey.c
> +++ b/drivers/usb/misc/chaoskey.c
> @@ -206,7 +206,9 @@ static int chaoskey_probe(struct usb_interface *interface,
>  	if (!dev->hwrng_registered)
>  		usb_err(interface, "Unable to register with hwrng");
>  
> +	usb_lock_device(udev);
>  	usb_enable_autosuspend(udev);
> +	usb_unlock_device(udev);

Not needed (indeed, actively harmful).  When this code runs it already 
holds the device lock, because it is part of a probe routine.

Alan Stern