linux-kernel - Re: [PATCH 1/2 V3 net] net: mana: Fix MANA VF unload when host is unresponsive

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Message-ID: <20230627084411.GC31802@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date:   Tue, 27 Jun 2023 01:44:11 -0700
From:   Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>
To:     Praveen Kumar <kumarpraveen@...ux.microsoft.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, longli@...rosoft.com,
        sharmaajay@...rosoft.com, leon@...nel.org, cai.huoqing@...ux.dev,
        ssengar@...ux.microsoft.com, vkuznets@...hat.com,
        tglx@...utronix.de, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, stable@...r.kernel.org,
        schakrabarti@...rosoft.com
Subject: Re: [PATCH 1/2 V3 net] net: mana: Fix MANA VF unload when host is
 unresponsive

On Mon, Jun 26, 2023 at 07:50:44PM +0530, Praveen Kumar wrote:
> On 6/26/2023 2:48 PM, souradeep chakrabarti wrote:
> > From: Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>
> > 
> > This patch addresses the VF unload issue, where mana_dealloc_queues()
> > gets stuck in infinite while loop, because of host unresponsiveness.
> > It adds a timeout in the while loop, to fix it.
> > 
> > Fixes: ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f (net: mana: Add a driver for
> > Microsoft Azure Network Adapter)
> > Signed-off-by: Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>
> > ---
> > V2 -> V3:
> > * Splitted the patch in two parts.
> > * Removed the unnecessary braces from mana_dealloc_queues().
> > ---
> >  drivers/net/ethernet/microsoft/mana/mana_en.c | 19 +++++++++++++++++--
> >  1 file changed, 17 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
> > index d907727c7b7a..cb5c43c3c47e 100644
> > --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> > +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
> > @@ -2329,7 +2329,10 @@ static int mana_dealloc_queues(struct net_device *ndev)
> >  {
> >  	struct mana_port_context *apc = netdev_priv(ndev);
> >  	struct gdma_dev *gd = apc->ac->gdma_dev;
> > +	unsigned long timeout;
> >  	struct mana_txq *txq;
> > +	struct sk_buff *skb;
> > +	struct mana_cq *cq;
> >  	int i, err;
> >  
> >  	if (apc->port_is_up)
> > @@ -2348,13 +2351,25 @@ static int mana_dealloc_queues(struct net_device *ndev)
> >  	 *
> >  	 * Drain all the in-flight TX packets
> >  	 */
> > +
> > +	timeout = jiffies + 120 * HZ;
> >  	for (i = 0; i < apc->num_queues; i++) {
> >  		txq = &apc->tx_qp[i].txq;
> > -
> > -		while (atomic_read(&txq->pending_sends) > 0)
> > +		while (atomic_read(&txq->pending_sends) > 0 &&
> > +		       time_before(jiffies, timeout))
> >  			usleep_range(1000, 2000);
> >  	}
> >  
> > +	for (i = 0; i < apc->num_queues; i++) {
> > +		txq = &apc->tx_qp[i].txq;
> > +		cq = &apc->tx_qp[i].tx_cq;
> > +		while (atomic_read(&txq->pending_sends)) {
> > +			skb = skb_dequeue(&txq->pending_skbs);
> > +			mana_unmap_skb(skb, apc);
> > +			napi_consume_skb(skb, cq->budget);
> > +			atomic_sub(1, &txq->pending_sends);
> > +		}
> > +	}
> 
> Can we combine these 2 loops into 1 something like this ?
> 
> 	for (i = 0; i < apc->num_queues; i++) {
> 		txq = &apc->tx_qp[i].txq;
> 		cq = &apc->tx_qp[i].tx_cq;
> 		while (atomic_read(&txq->pending_sends)) {
> 			if (time_before(jiffies, timeout)) {
> 				usleep_range(1000, 2000);
> 			} else {
> 				skb = skb_dequeue(&txq->pending_skbs);
> 				mana_unmap_skb(skb, apc);
> 				napi_consume_skb(skb, cq->budget);
> 				atomic_sub(1, &txq->pending_sends);
> 			}
> 		}
> 	}
We should free up the skbs only after timeout has happened or after all the
queues are looped.
> >  	/* We're 100% sure the queues can no longer be woken up, because
> >  	 * we're sure now mana_poll_tx_cq() can't be running.
> >  	 */