Re: [PATCH net-next] xen-netback: Follow-up patch for grant mapping series

[Ian Campbell <Ian.Campbell@citrix.com>]

On Thu, 2014-03-20 at 19:32 +0000, Zoltan Kiss wrote:
> Ian made some late comments about the grant mapping series, I incorporated the
> outcomes into this patch. Additional comments, refactoring etc.

I don't know how davem feels about merging these kinds of thing into one
patch but from my point of view the least thing to do is to enumerate
the cleanups -- so that people can verify that the patch does infact do
exactly what it says it does, no more, no less.

> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
> ---
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index 6837bfc..fa19538 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -576,15 +576,15 @@ void xenvif_disconnect(struct xenvif *vif)
>  void xenvif_free(struct xenvif *vif)
>  {
>  	int i, unmap_timeout = 0;
> -	/* Here we want to avoid timeout messages if an skb can be legitimatly
> -	 * stucked somewhere else. Realisticly this could be an another vif's
> +	/* Here we want to avoid timeout messages if an skb can be legitimately
> +	 * stuck somewhere else. Realistically this could be an another vif's
>  	 * internal or QDisc queue. That another vif also has this
>  	 * rx_drain_timeout_msecs timeout, but the timer only ditches the
>  	 * internal queue. After that, the QDisc queue can put in worst case
>  	 * XEN_NETIF_RX_RING_SIZE / MAX_SKB_FRAGS skbs into that another vif's
>  	 * internal queue, so we need several rounds of such timeouts until we
>  	 * can be sure that no another vif should have skb's from us. We are
> -	 * not sending more skb's, so newly stucked packets are not interesting
> +	 * not sending more skb's, so newly stuck packets are not interesting
>  	 * for us here.
>  	 */
>  	unsigned int worst_case_skb_lifetime = (rx_drain_timeout_msecs/1000) *
> @@ -599,6 +599,13 @@ void xenvif_free(struct xenvif *vif)
>  				netdev_err(vif->dev,
>  					   "Page still granted! Index: %x\n",
>  					   i);
> +			/* If there are still unmapped pages, reset the loop to
> +			 * start mchecking again. We shouldn't exit here until

"checking"

> +			 * dealloc thread and NAPI instance release all the
> +			 * pages. If a kernel bug cause the skbs stall

"causes the skbs to stall"

> +			 * somewhere, the interface couldn't be brought down
> +			 * properly.

I'm not sure what you are saying here exactly. Perhaps you means
s/couldn't/cannot/?

> +			 */
>  			i = -1;
>  		}
>  	}
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 1c336f6..0e46184b 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -56,7 +56,7 @@ bool separate_tx_rx_irq = 1;
>  module_param(separate_tx_rx_irq, bool, 0644);
>  
>  /* When guest ring is filled up, qdisc queues the packets for us, but we have
> - * to timeout them, otherwise other guests' packets can get stucked there
> + * to timeout them, otherwise other guests' packets can get stuck there
>   */
>  unsigned int rx_drain_timeout_msecs = 10000;
>  module_param(rx_drain_timeout_msecs, uint, 0444);
> @@ -99,6 +99,9 @@ static inline unsigned long idx_to_kaddr(struct xenvif *vif,
>  	return (unsigned long)pfn_to_kaddr(idx_to_pfn(vif, idx));
>  }
>  
> +#define callback_param(vif, pending_idx) \
> +	(vif->pending_tx_info[pending_idx].callback_struct)
> +
>  /* Find the containing VIF's structure from a pointer in pending_tx_info array
>   */
>  static inline struct xenvif* ubuf_to_vif(struct ubuf_info *ubuf)
> @@ -1025,12 +1028,12 @@ static void xenvif_fill_frags(struct xenvif *vif, struct sk_buff *skb)
>  		/* If this is not the first frag, chain it to the previous*/
>  		if (unlikely(prev_pending_idx == INVALID_PENDING_IDX))
>  			skb_shinfo(skb)->destructor_arg =
> -				&vif->pending_tx_info[pending_idx].callback_struct;
> +				&callback_param(vif, pending_idx);
>  		else if (likely(pending_idx != prev_pending_idx))
> -			vif->pending_tx_info[prev_pending_idx].callback_struct.ctx =
> -				&(vif->pending_tx_info[pending_idx].callback_struct);
> +			callback_param(vif, prev_pending_idx).ctx =
> +				&callback_param(vif, pending_idx);
>  
> -		vif->pending_tx_info[pending_idx].callback_struct.ctx = NULL;
> +		callback_param(vif, pending_idx).ctx = NULL;
>  		prev_pending_idx = pending_idx;
>  
>  		txp = &vif->pending_tx_info[pending_idx].req;
> @@ -1400,13 +1403,13 @@ static int xenvif_tx_submit(struct xenvif *vif)
>  		memcpy(skb->data,
>  		       (void *)(idx_to_kaddr(vif, pending_idx)|txp->offset),
>  		       data_len);
> -		vif->pending_tx_info[pending_idx].callback_struct.ctx = NULL;
> +		callback_param(vif, pending_idx).ctx = NULL;
>  		if (data_len < txp->size) {
>  			/* Append the packet payload as a fragment. */
>  			txp->offset += data_len;
>  			txp->size -= data_len;
>  			skb_shinfo(skb)->destructor_arg =
> -				&vif->pending_tx_info[pending_idx].callback_struct;
> +				&callback_param(vif, pending_idx);
>  		} else {
>  			/* Schedule a response immediately. */
>  			xenvif_idx_unmap(vif, pending_idx);
> @@ -1550,7 +1553,6 @@ static inline void xenvif_tx_dealloc_action(struct xenvif *vif)
>  					    idx_to_kaddr(vif, pending_idx),
>  					    GNTMAP_host_map,
>  					    vif->grant_tx_handle[pending_idx]);
> -			/* Btw. already unmapped? */
>  			xenvif_grant_handle_reset(vif, pending_idx);
>  			++gop;
>  		}
> @@ -1683,12 +1685,20 @@ void xenvif_idx_unmap(struct xenvif *vif, u16 pending_idx)
>  			    idx_to_kaddr(vif, pending_idx),
>  			    GNTMAP_host_map,
>  			    vif->grant_tx_handle[pending_idx]);
> -	/* Btw. already unmapped? */
>  	xenvif_grant_handle_reset(vif, pending_idx);
>  
>  	ret = gnttab_unmap_refs(&tx_unmap_op, NULL,
>  				&vif->mmap_pages[pending_idx], 1);
> -	BUG_ON(ret);
> +	if (ret) {
> +		netdev_err(vif->dev,
> +			   "Unmap fail: ret: %d pending_idx: %d host_addr: %llx handle: %x status: %d\n",
> +			   ret,
> +			   pending_idx,
> +			   tx_unmap_op.host_addr,
> +			   tx_unmap_op.handle,
> +			   tx_unmap_op.status);
> +		BUG();
> +	}
>  
>  	xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_OKAY);
>  }