Messages in this thread | | | Date | Fri, 18 Jul 2014 18:47:55 +0100 | From | Zoltan Kiss <> | Subject | Re: [PATCH net 1/4] xen-netback: Fix handling frag_list on grant op error path |
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On 18/07/14 16:24, Wei Liu wrote: > On Thu, Jul 17, 2014 at 08:09:49PM +0100, Zoltan Kiss wrote: >> The error handling for skb's with frag_list was completely wrong, it caused >> double unmap attempts to happen if the error was on the first skb. Move it to >> the right place in the loop. >> >> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com> >> Reported-by: Armin Zentai <armin.zentai@ezit.hu> >> Cc: netdev@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> Cc: xen-devel@lists.xenproject.org >> --- >> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c >> index 1844a47..604ff71 100644 >> --- a/drivers/net/xen-netback/netback.c >> +++ b/drivers/net/xen-netback/netback.c >> @@ -1030,10 +1030,16 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue, >> { >> struct gnttab_map_grant_ref *gop_map = *gopp_map; >> u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx; >> + /* This points to the shinfo of the actually checked skb, which could be >> + * either the first or the one on the frag_list >> + */ > > I think "checked skb" should be "skb being checked". Feel free to > disagree as I'm not native English speaker. :-/ > >> struct skb_shared_info *shinfo = skb_shinfo(skb); >> + /* If this is non-NULL, we are currently checking the frag_list skb, and >> + * this points to the shinfo of the first one >> + */ >> + struct skb_shared_info *first_shinfo = NULL; >> int nr_frags = shinfo->nr_frags; >> int i, err; >> - struct sk_buff *first_skb = NULL; >> >> /* Check status of header. */ >> err = (*gopp_copy)->status; >> @@ -1086,31 +1092,28 @@ check_frags: >> xenvif_idx_unmap(queue, pending_idx); >> } >> >> + /* And if we found the error while checking the frag_list, unmap >> + * the first skb's frags >> + */ >> + if (first_shinfo) { >> + for (j = 0; j < first_shinfo->nr_frags; j++) { >> + pending_idx = frag_get_pending_idx(&first_shinfo->frags[j]); >> + xenvif_idx_unmap(queue, pending_idx); >> + } >> + } >> + >> /* Remember the error: invalidate all subsequent fragments. */ >> err = newerr; >> } >> >> - if (skb_has_frag_list(skb)) { >> - first_skb = skb; >> - skb = shinfo->frag_list; >> - shinfo = skb_shinfo(skb); >> + if (skb_has_frag_list(skb) && !first_shinfo) { > > Will it ever come to the point that we have another skb in this skb's > frag list? Is there any reason prevents you from looping over the > (possible) subsequent skbs? I guess if the error is deep in the list > it's a bit hard to bookkeep... > >> + first_shinfo = skb_shinfo(skb); >> + shinfo = skb_shinfo(skb_shinfo(skb)->frag_list); > > In that case I would suggest you add > BUG_ON(skb_has_frag_list(skb_shinfo(skb)->frag_list)). I think having > more nested frag_list should be a bug in current design.
There are already 3 things which prevents this - in count_requests we drop the packet if it has more than XEN_NETBK_LEGACY_SLOTS_MAX slots - in get_requests there is a BUG_ON(frag_overflow > MAX_SKB_FRAGS), which shouldn't really due to the prev point - in the same funciont we create a frag_list skb exactly once
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