linux-kernel - Re: [PATCH v3 1/3] usb: ucsi: Add missing ppm

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Message-ID: <ZbDFoGL1GnxZAXER@kuha.fi.intel.com>
Date: Wed, 24 Jan 2024 10:09:04 +0200
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: "Christian A. Ehrhardt" <lk@...e.de>
Cc: linux-usb@...r.kernel.org, Dell.Client.Kernel@...l.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Jack Pham <quic_jackp@...cinc.com>,
	Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
	Samuel Čavoj <samuel@...oj.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] usb: ucsi: Add missing ppm_lock

On Sun, Jan 21, 2024 at 09:41:21PM +0100, Christian A. Ehrhardt wrote:
> Calling ->sync_write must be done while holding the PPM lock as
> the mailbox logic does not support concurrent commands.
> 
> At least since the addition of partner task this means that
> ucsi_acknowledge_connector_change should be called with the
> PPM lock held as it calls ->sync_write.
> 
> Thus protect the only call to ucsi_acknowledge_connector_change
> with the PPM. All other calls to ->sync_write already happen
> under the PPM lock.
> 
> Fixes: b9aa02ca39a4 ("usb: typec: ucsi: Add polling mechanism for partner tasks like alt mode checking")
> Cc: stable@...r.kernel.org
> Signed-off-by: Christian A. Ehrhardt <lk@...e.de>
> ---
>  drivers/usb/typec/ucsi/ucsi.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
> index 61b64558f96c..8f9dff993b3d 100644
> --- a/drivers/usb/typec/ucsi/ucsi.c
> +++ b/drivers/usb/typec/ucsi/ucsi.c
> @@ -935,7 +935,9 @@ static void ucsi_handle_connector_change(struct work_struct *work)
>  
>  	clear_bit(EVENT_PENDING, &con->ucsi->flags);
>  
> +	mutex_lock(&ucsi->ppm_lock);
>  	ret = ucsi_acknowledge_connector_change(ucsi);
> +	mutex_unlock(&ucsi->ppm_lock);
>  	if (ret)
>  		dev_err(ucsi->dev, "%s: ACK failed (%d)", __func__, ret);

Is this really actually fixing some issue? The function has already
taken the connector lock, so what exactly could happen without this?

thanks,

-- 
heikki