netdev - Re: [PATCH net] sfc: check for NULL efx->ptp_data in efx_ptp

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Message-ID: <1393285210.6823.109.camel@deadeye.wl.decadent.org.uk>
Date:	Mon, 24 Feb 2014 23:40:10 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Edward Cree <ecree@...arflare.com>
Cc:	netdev@...r.kernel.org, Shradha Shah <sshah@...arflare.com>
Subject: Re: [PATCH net] sfc: check for NULL efx->ptp_data in efx_ptp_event

On Mon, 2014-02-24 at 19:39 +0000, Edward Cree wrote:
> If we receive a PTP event from the NIC when we haven't set up PTP state
> in the driver, we attempt to read through a NULL pointer efx->ptp_data,
> triggering a panic.
> 
> Signed-off-by: Edward Cree <ecree@...arflare.com>
> ---
> While this shouldn't happen with existing released firmware, future
> sfn7322f firmware is planned to enable PPS irrespective of whether
> timestamping (and thus PTP) is enabled.  We are considering workarounds,
> but this defensive patch seemed like a good idea anyway in case the
> firmware gets in a muddle.
> Also, in principle this shouldn't happen on 3.14+ kernels as the driver
> should always set up PTP state at probe time (though there might still
> be a race against the firmware sending its first PPS), however 3.12 and
> 3.13 both supported EF10 but not PTP-on-EF10 and thus they never set up
> the PTP state; hence this fix should also be backported to those series.

Good thinking.

> --- linux-3.13/drivers/net/ethernet/sfc/ptp.c.orig	2014-01-20
> 02:40:07.000000000 +0000
> +++ linux-3.13/drivers/net/ethernet/sfc/ptp.c	2014-02-24
> 17:46:31.753497000 +0000

This patch has been word-wrapped and can't be applied; see
Documentation/email-clients.txt

Ben.

> @@ -1360,6 +1360,13 @@ void efx_ptp_event(struct efx_nic *efx,
>  	struct efx_ptp_data *ptp = efx->ptp_data;
>  	int code = EFX_QWORD_FIELD(*ev, MCDI_EVENT_CODE);
> 
> +	if (!ptp) {
> +		if (net_ratelimit())
> +			netif_warn(efx, drv, efx->net_dev,
> +				   "Received PTP event but PTP not set up\n");
> +		return;
> +	}
> +
>  	if (!ptp->enabled)
>  		return;
> 

-- 
Ben Hutchings
Beware of bugs in the above code;
I have only proved it correct, not tried it. - Donald Knuth

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