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

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Message-ID: <CABBYNZL4tEBTT3Hrf3JUGNuseLg1SNLmazo88EitmMfhUWUQxw@mail.gmail.com>
Date: Thu, 13 Feb 2025 09:22:28 -0500
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Hsin-chen Chuang <chharry@...gle.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

Hi Greg,

On Thu, Feb 13, 2025 at 8:45 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Thu, Feb 13, 2025 at 09:33:34PM +0800, Hsin-chen Chuang wrote:
> > 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.
>
> That feels crazy.
>
> > 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?
>
> If you add a new device in the tree, it HAS to work properly with the
> driver core (i.e. life cycles are unique, you can't have empty release
> functions, etc.)  Put it on the proper bus it belongs to, bind the
> needed drivers to it, and have it work that way, don't make a "fake"
> device for no good reason.

Well we could just introduce it to USB device, since alternate setting
is a concept that is coming from there, but apparently the likes of
/sys/bus/usb/devices/usbX/bAlternateSetting is read-only, some
Bluetooth profiles (HFP) requires switching the alternate setting and
because Google is switching to handle this via userspace thus why
there was this request to add a new sysfs to control it.

-- 
Luiz Augusto von Dentz