[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH net 1/4] xen-netback: Fix handling frag_list on grant op error path
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@xxxxxxxxxx> Reported-by: Armin Zentai <armin.zentai@xxxxxxx> Cc: netdev@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx --- 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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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