From 801dafc3218c23ba1ea39f409b962113604f64bc Mon Sep 17 00:00:00 2001 From: Jon Maloy Date: Tue, 30 Jul 2019 16:23:18 +0200 Subject: tipc: reduce risk of wakeup queue starvation [ Upstream commit 7c5b42055964f587e55bd87ef334c3a27e95d144 ] In commit 365ad353c256 ("tipc: reduce risk of user starvation during link congestion") we allowed senders to add exactly one list of extra buffers to the link backlog queues during link congestion (aka "oversubscription"). However, the criteria for when to stop adding wakeup messages to the input queue when the overload abates is inaccurate, and may cause starvation problems during very high load. Currently, we stop adding wakeup messages after 10 total failed attempts where we find that there is no space left in the backlog queue for a certain importance level. The counter for this is accumulated across all levels, which may lead the algorithm to leave the loop prematurely, although there may still be plenty of space available at some levels. The result is sometimes that messages near the wakeup queue tail are not added to the input queue as they should be. We now introduce a more exact algorithm, where we keep adding wakeup messages to a level as long as the backlog queue has free slots for the corresponding level, and stop at the moment there are no more such slots or when there are no more wakeup messages to dequeue. Fixes: 365ad35 ("tipc: reduce risk of user starvation during link congestion") Reported-by: Tung Nguyen Acked-by: Ying Xue Signed-off-by: Jon Maloy Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- net/tipc/link.c | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-) (limited to 'net') diff --git a/net/tipc/link.c b/net/tipc/link.c index da749916faac..82e4e0e152d1 100644 --- a/net/tipc/link.c +++ b/net/tipc/link.c @@ -811,18 +811,31 @@ static int link_schedule_user(struct tipc_link *l, struct tipc_msg *hdr) */ void link_prepare_wakeup(struct tipc_link *l) { + struct sk_buff_head *wakeupq = &l->wakeupq; + struct sk_buff_head *inputq = l->inputq; struct sk_buff *skb, *tmp; - int imp, i = 0; + struct sk_buff_head tmpq; + int avail[5] = {0,}; + int imp = 0; + + __skb_queue_head_init(&tmpq); - skb_queue_walk_safe(&l->wakeupq, skb, tmp) { + for (; imp <= TIPC_SYSTEM_IMPORTANCE; imp++) + avail[imp] = l->backlog[imp].limit - l->backlog[imp].len; + + skb_queue_walk_safe(wakeupq, skb, tmp) { imp = TIPC_SKB_CB(skb)->chain_imp; - if (l->backlog[imp].len < l->backlog[imp].limit) { - skb_unlink(skb, &l->wakeupq); - skb_queue_tail(l->inputq, skb); - } else if (i++ > 10) { - break; - } + if (avail[imp] <= 0) + continue; + avail[imp]--; + __skb_unlink(skb, wakeupq); + __skb_queue_tail(&tmpq, skb); } + + spin_lock_bh(&inputq->lock); + skb_queue_splice_tail(&tmpq, inputq); + spin_unlock_bh(&inputq->lock); + } void tipc_link_reset(struct tipc_link *l) -- cgit v1.2.3