netdev - Re: [PATCH net v3] ravb: Fix races between ravb_tx_timeout

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Date: Wed, 15 Nov 2023 21:37:16 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>, Simon
 Horman <horms@...nel.org>
Subject: Re: [PATCH net v3] ravb: Fix races between ravb_tx_timeout_work() and
 net related ops

On 11/15/23 5:26 AM, Yoshihiro Shimoda wrote:

> Fix races between ravb_tx_timeout_work() and functions of net_device_ops
> and ethtool_ops by using rtnl_trylock() and rtnl_unlock(). Note that
> since ravb_close() is under the rtnl lock and calls cancel_work_sync(),
> ravb_tx_timeout_work() should calls rtnl_trylock(). Otherwise, a deadlock
> may happen in ravb_tx_timeout_work() like below:
> 
> CPU0			CPU1
> 			ravb_tx_timeout()
> 			schedule_work()
> ...
> __dev_close_many()
> // Under rtnl lock
> ravb_close()
> cancel_work_sync()
> // Waiting
> 			ravb_tx_timeout_work()
> 			rtnl_lock()
> 			// This is possible to cause a deadlock
> 
> And, if rtnl_trylock() fails and the netif is still running,
> rescheduling the work with 1 msec delayed. So, using
> schedule_delayed_work() instead of schedule_work().
> 
> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>

   Hm, I haven't reviewed this version... :-)

> Reviewed-by: Simon Horman <horms@...nel.org>
[...]
> diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
> index e0f8276cffed..e9bb8ee3ba2d 100644
> --- a/drivers/net/ethernet/renesas/ravb.h
> +++ b/drivers/net/ethernet/renesas/ravb.h
> @@ -1081,7 +1081,7 @@ struct ravb_private {
>  	u32 cur_tx[NUM_TX_QUEUE];
>  	u32 dirty_tx[NUM_TX_QUEUE];
>  	struct napi_struct napi[NUM_RX_QUEUE];
> -	struct work_struct work;
> +	struct delayed_work work;

   Not sure this is justified...
   Then again, what do I know about workqueues? Not much... :-)

[...]
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index c70cff80cc99..ca7db8a5b412 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -1863,17 +1863,24 @@ static void ravb_tx_timeout(struct net_device *ndev, unsigned int txqueue)
>  	/* tx_errors count up */
>  	ndev->stats.tx_errors++;
>  
> -	schedule_work(&priv->work);
> +	schedule_delayed_work(&priv->work, 0);
>  }
>  
>  static void ravb_tx_timeout_work(struct work_struct *work)
>  {
> -	struct ravb_private *priv = container_of(work, struct ravb_private,
> +	struct delayed_work *dwork = to_delayed_work(work);
> +	struct ravb_private *priv = container_of(dwork, struct ravb_private,
>  						 work);
>  	const struct ravb_hw_info *info = priv->info;
>  	struct net_device *ndev = priv->ndev;
>  	int error;
>  
> +	if (!rtnl_trylock()) {
> +		if (netif_running(ndev))
> +			schedule_delayed_work(&priv->work, msecs_to_jiffies(10));

   The delay is rather arbitrary. Why not e.g. 1 ms?

[...]

MBR, Sergey