linux-kernel - Re: [PATCH v1 2/2] usb: gadget: udc: core: Prevent redundant calls to pullup

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Date:   Wed, 5 Apr 2023 23:35:47 -0700
From:   Badhri Jagan Sridharan <badhri@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     stern@...land.harvard.edu, colin.i.king@...il.com,
        xuetao09@...wei.com, quic_eserrao@...cinc.com,
        water.zhangjiantao@...wei.com, peter.chen@...escale.com,
        balbi@...com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v1 2/2] usb: gadget: udc: core: Prevent redundant calls to pullup

On Wed, Apr 5, 2023 at 10:16 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Apr 05, 2023 at 09:31:33AM +0000, Badhri Jagan Sridharan wrote:
> > usb_gadget_connect calls gadget->ops->pullup without
> > checking whether gadget->connected was previously set.
> > Make this symmetric to usb_gadget_disconnect by returning
> > early if gadget->connected is already set.
> >
> > Cc: stable@...r.kernel.org
> >
> > Signed-off-by: Badhri Jagan Sridharan <badhri@...gle.com>
> > Fixes: 5a1da544e572 ("usb: gadget: core: do not try to disconnect gadget if it is not connected")
>
> Same changelog comment as before.
Thanks for the feedback Greg ! Have fixed it in v2.

>
> > ---
> >  drivers/usb/gadget/udc/core.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> > index 890f92cb6344..7eeaf7dbb350 100644
> > --- a/drivers/usb/gadget/udc/core.c
> > +++ b/drivers/usb/gadget/udc/core.c
> > @@ -708,6 +708,9 @@ int usb_gadget_connect(struct usb_gadget *gadget)
> >               goto out;
> >       }
> >
> > +     if (gadget->connected)
> > +             goto out;
> > +
>
> What prevents this connected value from changing right after you check
> this?

Nothing in V1 :) However, in v2, the newly introduced mutex guards
gadget->connected
as well.

>
> thanks,
>
> greg k-h