linux-kernel - Re: [PATCH v0 16/42] USB: Check notifier registration return value

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Message-ID: <20211108140553.GA1666297@rowland.harvard.edu>
Date:   Mon, 8 Nov 2021 09:05:53 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org
Subject: Re: [PATCH v0 16/42] USB: Check notifier registration return value

On Mon, Nov 08, 2021 at 11:11:31AM +0100, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Avoid homegrown notifier registration checks.

This is a rather misleading description.  The patch does exactly the 
opposite: It _adds_ a homegrown notifier registration check.  (Homegrown 
in the sense that the check is made by the individual caller rather than 
being centralized in the routine being called.)

Alan Stern

> No functional changes.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: linux-usb@...r.kernel.org
> ---
>  drivers/usb/core/notify.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/notify.c b/drivers/usb/core/notify.c
> index e6143663778f..80d1bfa61887 100644
> --- a/drivers/usb/core/notify.c
> +++ b/drivers/usb/core/notify.c
> @@ -28,7 +28,8 @@ static BLOCKING_NOTIFIER_HEAD(usb_notifier_list);
>   */
>  void usb_register_notify(struct notifier_block *nb)
>  {
> -	blocking_notifier_chain_register(&usb_notifier_list, nb);
> +	if (blocking_notifier_chain_register(&usb_notifier_list, nb))
> +		pr_warn("USB change notifier already registered\n");
>  }
>  EXPORT_SYMBOL_GPL(usb_register_notify);
>  
> -- 
> 2.29.2
>