Re: [PATCH v6 net-next 1/5] net: mscc: ocelot: fix mutex lock error during ethtool stats read

From: Vladimir Oltean <vladimir.oltean@nxp.com>
To: Colin Foster <colin.foster@in-advantage.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	"UNGLinuxDriver@microchip.com" <UNGLinuxDriver@microchip.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	Vladimir Oltean <olteanv@gmail.com>
Subject: Re: [PATCH v6 net-next 1/5] net: mscc: ocelot: fix mutex lock error during ethtool stats read
Date: Thu, 10 Feb 2022 09:50:52 +0000	[thread overview]
Message-ID: <20220210095051.b7rgpy6muvqjnih2@skbuf> (raw)
In-Reply-To: <20220210041345.321216-2-colin.foster@in-advantage.com>

On Wed, Feb 09, 2022 at 08:13:41PM -0800, Colin Foster wrote:
> An ongoing workqueue populates the stats buffer. At the same time, a user
> might query the statistics. While writing to the buffer is mutex-locked,
> reading from the buffer wasn't. This could lead to buggy reads by ethtool.
> 
> Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
> Fixes: a556c76adc052 ("net: mscc: Add initial Ocelot switch support")
> Reported-by: Vladimir Oltean <olteanv@gmail.com>

I reported this using vladimir.oltean@nxp.com btw.

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

If you hurry and resend this against the "net" tree, you might catch
this week's pull request, since the last one was on Feb 3->4:
https://patchwork.kernel.org/project/netdevbpf/patch/20220204000428.2889873-1-kuba@kernel.org/
Then "net" will be merged into "net-next" probably the next day or so,
and you can resend patches 2-5 towards "net-next".

> ---
>  drivers/net/ethernet/mscc/ocelot.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> index 455293aa6343..6933dff1dd37 100644
> --- a/drivers/net/ethernet/mscc/ocelot.c
> +++ b/drivers/net/ethernet/mscc/ocelot.c
> @@ -1737,12 +1737,11 @@ void ocelot_get_strings(struct ocelot *ocelot, int port, u32 sset, u8 *data)
>  }
>  EXPORT_SYMBOL(ocelot_get_strings);
>  
> +/* Caller must hold &ocelot->stats_lock */
>  static void ocelot_update_stats(struct ocelot *ocelot)
>  {
>  	int i, j;
>  
> -	mutex_lock(&ocelot->stats_lock);
> -
>  	for (i = 0; i < ocelot->num_phys_ports; i++) {
>  		/* Configure the port to read the stats from */
>  		ocelot_write(ocelot, SYS_STAT_CFG_STAT_VIEW(i), SYS_STAT_CFG);
> @@ -1761,8 +1760,6 @@ static void ocelot_update_stats(struct ocelot *ocelot)
>  					      ~(u64)U32_MAX) + val;
>  		}
>  	}
> -
> -	mutex_unlock(&ocelot->stats_lock);
>  }
>  
>  static void ocelot_check_stats_work(struct work_struct *work)
> @@ -1771,7 +1768,9 @@ static void ocelot_check_stats_work(struct work_struct *work)
>  	struct ocelot *ocelot = container_of(del_work, struct ocelot,
>  					     stats_work);
>  
> +	mutex_lock(&ocelot->stats_lock);
>  	ocelot_update_stats(ocelot);
> +	mutex_unlock(&ocelot->stats_lock);
>  
>  	queue_delayed_work(ocelot->stats_queue, &ocelot->stats_work,
>  			   OCELOT_STATS_CHECK_DELAY);
> @@ -1781,12 +1780,16 @@ void ocelot_get_ethtool_stats(struct ocelot *ocelot, int port, u64 *data)
>  {
>  	int i;
>  
> +	mutex_lock(&ocelot->stats_lock);
> +
>  	/* check and update now */
>  	ocelot_update_stats(ocelot);
>  
>  	/* Copy all counters */
>  	for (i = 0; i < ocelot->num_stats; i++)
>  		*data++ = ocelot->stats[port * ocelot->num_stats + i];
> +
> +	mutex_unlock(&ocelot->stats_lock);
>  }
>  EXPORT_SYMBOL(ocelot_get_ethtool_stats);
>  
> -- 
> 2.25.1
>