netdev - RE: [PATCH net v2] ravb: Fix races between ravb_tx_timeout

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Date: Wed, 15 Nov 2023 02:09:41 +0000
From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To: Sergey Shtylyov <s.shtylyov@....ru>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH net v2] ravb: Fix races between ravb_tx_timeout_work() and
 net related ops

Hello Sergey,

> From: Sergey Shtylyov, Sent: Thursday, October 19, 2023 9:36 PM
> 
> Hello!
> 
> On 10/19/23 2:33 PM, 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
> >
> > Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> 
> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>

Thank you for your review!

> [...]
> > diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> > index 0ef0b88b7145..300c1885e1e1 100644
> > --- a/drivers/net/ethernet/renesas/ravb_main.c
> > +++ b/drivers/net/ethernet/renesas/ravb_main.c
> > @@ -1874,6 +1874,9 @@ static void ravb_tx_timeout_work(struct work_struct *work)
> >  	struct net_device *ndev = priv->ndev;
> >  	int error;
> >
> > +	if (!rtnl_trylock())
> > +		return;
> 
>    I wonder if we should reschedule the work here...

I think so. But, it should reschedule the work if the netif is still running because
Use-after-free issue happens again when cancel_work_sync() is calling. Also, I also think
we should use schedule_delayed_work() instead. So, I'll submit such a patch as v3.

Best regards,
Yoshihiro Shimoda

> [...]
> 
> MBR, Sergey