netdev - RE: [PATCH 3/3] dpaa2-eth: Avoid unbounded while loops

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Date:   Mon, 7 Oct 2019 10:49:39 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>
Subject: RE: [PATCH 3/3] dpaa2-eth: Avoid unbounded while loops

> Subject: Re: [PATCH 3/3] dpaa2-eth: Avoid unbounded while loops
> 
> On Fri, Oct 04, 2019 at 12:21:33PM +0300, Ioana Ciornei wrote:
> > From: Ioana Radulescu <ruxandra.radulescu@....com>
> >
> > Throughout the driver there are several places where we wait
> > indefinitely for DPIO portal commands to be executed, while the portal
> > returns a busy response code.
> >
> > Even though in theory we are guaranteed the portals become available
> > eventually, in practice the QBMan hardware module may become
> > unresponsive in various corner cases.
> >
> > Make sure we can never get stuck in an infinite while loop by adding a
> > retry counter for all portal commands.
> >
> > Signed-off-by: Ioana Radulescu <ruxandra.radulescu@....com>
> > Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>
> > ---
> >  drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c | 30
> > ++++++++++++++++++++----
> > drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.h |  8 +++++++
> >  2 files changed, 33 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> > b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> > index 2c5072fa9aa0..29702756734c 100644
> > --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> > +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> > @@ -221,6 +221,7 @@ static void xdp_release_buf(struct dpaa2_eth_priv
> *priv,
> >  			    struct dpaa2_eth_channel *ch,
> >  			    dma_addr_t addr)
> >  {
> > +	int retries = 0;
> >  	int err;
> >
> >  	ch->xdp.drop_bufs[ch->xdp.drop_cnt++] = addr; @@ -229,8 +230,11
> @@
> > static void xdp_release_buf(struct dpaa2_eth_priv *priv,
> >
> >  	while ((err = dpaa2_io_service_release(ch->dpio, priv->bpid,
> >  					       ch->xdp.drop_bufs,
> > -					       ch->xdp.drop_cnt)) == -EBUSY)
> > +					       ch->xdp.drop_cnt)) == -EBUSY) {
> > +		if (retries++ >= DPAA2_ETH_SWP_BUSY_RETRIES)
> > +			break;
> >  		cpu_relax();
> > +	}
> >
> >  	if (err) {
> >  		free_bufs(priv, ch->xdp.drop_bufs, ch->xdp.drop_cnt); @@ -
> 458,7
> > +462,7 @@ static int consume_frames(struct dpaa2_eth_channel *ch,
> >  	struct dpaa2_eth_fq *fq = NULL;
> >  	struct dpaa2_dq *dq;
> >  	const struct dpaa2_fd *fd;
> > -	int cleaned = 0;
> > +	int cleaned = 0, retries = 0;
> >  	int is_last;
> >
> >  	do {
> > @@ -469,6 +473,11 @@ static int consume_frames(struct dpaa2_eth_channel
> *ch,
> >  			 * the store until we get some sort of valid response
> >  			 * token (either a valid frame or an "empty dequeue")
> >  			 */
> > +			if (retries++ >= DPAA2_ETH_SWP_BUSY_RETRIES) {
> > +				netdev_err_once(priv->net_dev,
> > +						"Unable to read a valid
> dequeue response\n");
> > +				return 0;
> > +			}
> >  			continue;
> 
> Hi Ioana
> 
> It seems a bit odd that here you could return -ETIMEDOUT, but you print an
> error, and return 0. But in the two cases above in void functions, you don't print
> anything.
> 
> Please at least return -ETIMEDOUT when you can.

Hi Andrew,

That's a good point. I'll send out a v2 fixing this.

Thanks,
Ioana

> 
>        Andrew