linux-kernel - Re: [PATCH v5 2/3] usb: gadget: udc: core: Invoke usb_gadget

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Message-ID: <0125d274-bac3-41e1-bd29-156a3bfcc995@rowland.harvard.edu>
Date:   Wed, 31 May 2023 18:55:32 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Badhri Jagan Sridharan <badhri@...gle.com>
Cc:     gregkh@...uxfoundation.org, colin.i.king@...il.com,
        xuetao09@...wei.com, quic_eserrao@...cinc.com,
        water.zhangjiantao@...wei.com, francesco@...cini.it,
        alistair@...stair23.me, stephan@...hold.net, bagasdotme@...il.com,
        luca@...tu.xyz, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v5 2/3] usb: gadget: udc: core: Invoke usb_gadget_connect
 only when started

On Wed, May 31, 2023 at 03:40:26PM -0700, Badhri Jagan Sridharan wrote:
> On Wed, May 31, 2023 at 10:55 AM Alan Stern <stern@...land.harvard.edu> wrote:
> >
> > On Wed, May 31, 2023 at 04:02:02AM +0000, Badhri Jagan Sridharan wrote:
> > > usb_udc_connect_control() does not check to see if the udc has already
> > > been started. This causes gadget->ops->pullup to be called through
> > > usb_gadget_connect() when invoked from usb_udc_vbus_handler() even
> > > before usb_gadget_udc_start() is called. Guard this by checking for
> > > udc->started in usb_udc_connect_control() before invoking
> > > usb_gadget_connect().
> >
> > After a merged version of patches 1/3 and 3/3 have been applied, it
> > seems like most of this will not be needed any more.  Maybe not any of
> > it.
> 
> Without the connect_lock introduced in this patch, wouldn't the
> usb_gadget_connect()/
> usb_gadget_disconnect() through soft_connect_store() race against
> usb_gadget_connect()/ usb_gadget_disconnect() through
> usb_udc_connect_control() ?

Okay, yes, that's a good point.  It needs to be mentioned in the patch 
description so that people will understand it is the real reason for 
this change.

Alan Stern