netdev - Re: [PATCH] wireless: rtl8187: replace udev with usb_get

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Date:   Sun, 25 Jul 2021 08:33:01 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Hin-Tak Leung <htl10@...rs.sourceforge.net>
Cc:     Herton Ronaldo Krzesinski <herton@...onical.com>,
        Larry Finger <larry.finger@...inger.net>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Salah Triki <salah.triki@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wireless: rtl8187: replace udev with usb_get_dev()

On Sat, Jul 24, 2021 at 08:54:34PM +0000, Hin-Tak Leung wrote:
>  
> 
> On Saturday, 24 July 2021, 19:35:12 BST, Salah Triki <salah.triki@...il.com> wrote:
> 
> 
> > Replace udev with usb_get_dev() in order to make code cleaner.
> 
> > Signed-off-by: Salah Triki <salah.triki@...il.com>
> > ---
> > drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> 
> > diff --git a/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c b/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c
> > index eb68b2d3caa1..30bb3c2b8407 100644
> > --- a/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c
> > +++ b/drivers/net/wireless/realtek/rtl818x/rtl8187/dev.c
> > @@ -1455,9 +1455,7 @@ static int rtl8187_probe(struct usb_interface *intf,
> 
> >     SET_IEEE80211_DEV(dev, &intf->dev);
> >     usb_set_intfdata(intf, dev);
> > -    priv->udev = udev;
> > -
> > -    usb_get_dev(udev);
> > +    priv->udev = usb_get_dev(udev);
> 
> >     skb_queue_head_init(&priv->rx_queue);
> 
> > -- 
> > 2.25.1
> 
> It is not cleaner - the change is not functionally equivalent. Before the change, the reference count is increased after the assignment; and after the change, before the assignment. So my question is, does the reference count increasing a little earlier matters? What can go wrong between very short time where the reference count increases, and priv->udev not yet assigned? I think there might be a race condition where the probbe function is called very shortly twice.
> Especially if the time of running the reference count function is non-trivial.

Probe functions are called in order, this should not be an issue.

This patch changes nothing, I do not think it is needed at all.

thanks,

greg k-h