netdev - Re: [PATCH v4 1/3] Bluetooth: Fix possible race with userspace of sysfs isoc

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Message-ID: <CADg1FFdbKx3z+SPWFmY4+xZmewh0MnnZp_gmYEdY0z-mxutmEw@mail.gmail.com>
Date: Thu, 13 Feb 2025 21:33:34 +0800
From: Hsin-chen Chuang <chharry@...gle.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: luiz.dentz@...il.com, linux-bluetooth@...r.kernel.org, 
	chromeos-bluetooth-upstreaming@...omium.org, 
	Hsin-chen Chuang <chharry@...omium.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Johan Hedberg <johan.hedberg@...il.com>, Marcel Holtmann <marcel@...tmann.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Ying Hsu <yinghsu@...omium.org>, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v4 1/3] Bluetooth: Fix possible race with userspace of
 sysfs isoc_alt

On Thu, Feb 13, 2025 at 8:10 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> A: http://en.wikipedia.org/wiki/Top_post
> Q: Were do I find info about this thing called top-posting?
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
>
> A: No.
> Q: Should I include quotations after my reply?
>
> http://daringfireball.net/2007/07/on_top
>
> On Thu, Feb 13, 2025 at 07:57:15PM +0800, Hsin-chen Chuang wrote:
> > The btusb driver data is allocated by devm_kzalloc and is
> > automatically freed on driver detach, so I guess we don't have
> > anything to do here.
>
> What?  A struct device should NEVER be allocated with devm_kzalloc.
> That's just not going to work at all.

Noted. Perhaps that needs to be refactored together.

>
> > Or perhaps we should move btusb_disconnect's content here? Luiz, what
> > do you think?
>
> I think something is really wrong here.  Why are you adding a new struct
> device to the system?  What requires that?  What is this new device
> going to be used for?

The new device is only for exposing a new sysfs attribute.

So originally we had a device called hci_dev, indicating the
implementation of the Bluetooth HCI layer. hci_dev is directly the
child of the usb_interface (the Bluetooth chip connected through USB).
Now I would like to add an attribute for something that's not defined
in the HCI layer, but lower layer only in Bluetooth USB.
Thus we want to rephrase the structure: usb_interface -> btusb (new
device) -> hci_dev, and then we could place the new attribute in the
new device.

Basically I kept the memory management in btusb unchanged in this
patch, as the new device is only used for a new attribute.
Would you suggest we revise the memory management since we added a
device in this module?

>
> confused,
>
>
> greg k-h

-- 
Best Regards,
Hsin-chen