linux-kernel - Re: [PATCH 06/10] Revert "usb: typec: displayport: Receive DP Status Update NAK request exit dp altmode"

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Message-ID: <CAMMMRMebxSLorxTRzre6MDEn0bdC3hrNVQzZyf0NH=TNUk+YGw@mail.gmail.com>
Date: Mon, 16 Jun 2025 21:42:53 +0200
From: Andrei Kuchynski <akuchynski@...omium.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Dmitry Baryshkov <lumag@...nel.org>, 
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>, Jameson Thies <jthies@...gle.com>, 
	Benson Leung <bleung@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	Guenter Roeck <groeck@...omium.org>, Pooja Katiyar <pooja.katiyar@...el.com>, 
	Badhri Jagan Sridharan <badhri@...gle.com>, RD Babiera <rdbabiera@...gle.com>, linux-usb@...r.kernel.org, 
	linux-kernel@...r.kernel.org, chrome-platform@...ts.linux.dev
Subject: Re: [PATCH 06/10] Revert "usb: typec: displayport: Receive DP Status
 Update NAK request exit dp altmode"

On Mon, Jun 16, 2025 at 4:15 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Jun 16, 2025 at 01:31:43PM +0000, Andrei Kuchynski wrote:
> > This reverts commit b4b38ffb38c91afd4dc387608db26f6fc34ed40b.
> >
> > The commit introduced a deadlock with the cros_ec_typec driver.
> > The deadlock occurs due to a recursive lock acquisition of
> > `cros_typec_altmode_work::mutex`.
> > The call chain is as follows:
> > 1. cros_typec_altmode_work() acquires the mutex
> > 2. typec_altmode_vdm() -> dp_altmode_vdm() ->
> > 3. typec_altmode_exit() -> cros_typec_altmode_exit()
> > 4. cros_typec_altmode_exit() attempts to acquire the mutex again
> >
> > This revert is considered safe as no other known driver sends back
> > DP_CMD_STATUS_UPDATE command with the NAK flag.
> >
> > Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>
> > ---
> >  drivers/usb/typec/altmodes/displayport.c | 4 ----
> >  1 file changed, 4 deletions(-)
>
> Why isn't this being sent as a separate patch for 6.16-final?  And why
> not put a fixes: line?
>

Hi Greg,

The issue will emerge only after this series is applied, so 6.16
remains secure as this code is not executable.
I will submit it as a separate patch, with the relevant tags included.

Thanks,
Andrei