Commit fe926f26 authored Jan 15, 2015 by Eric Dumazet Committed by Trilok Soni Jan 27, 2015

net: rps: fix cpu unplug



softnet_data.input_pkt_queue is protected by a spinlock that we must
hold when transferring packets from victim queue to an active one.
This is because other cpus could still be trying to enqueue packets
into victim queue.

A second problem is that when we transfert the NAPI poll_list from
victim to current cpu, we absolutely need to special case the percpu
backlog, because we do not want to add complex locking to protect
process_queue : Only owner cpu is allowed to manipulate it, unless
cpu is offline.

Based on initial patch from Prasad Sodagudi &
Subash Abhinov Kasiviswanathan.

This version is better because we do not slow down packet processing,
only make migration safer.

Change-Id: I6468cc74779b126ce0565f8bd6cc39514b14eb38
Reported-by: Prasad Sodagudi <psodagud@codeaurora.org>
Reported-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Git-commit: ac64da0b83d82abe62f78b3d0e21cca31aea24fa
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Trilok Soni <tsoni@codeaurora.org>

parent 67c0ac5f

net/core/dev.c

+15 −5

Original line number	Diff line number	Diff line
		@@ -6015,10 +6015,20 @@ static int dev_cpu_callback(struct notifier_block *nfb,
		oldsd->output_queue = NULL;
		oldsd->output_queue_tailp = &oldsd->output_queue;
		}
		/* Append NAPI poll list from offline CPU. */
		if (!list_empty(&oldsd->poll_list)) {
		list_splice_init(&oldsd->poll_list, &sd->poll_list);
		raise_softirq_irqoff(NET_RX_SOFTIRQ);
		/* Append NAPI poll list from offline CPU, with one exception :
		* process_backlog() must be called by cpu owning percpu backlog.
		* We properly handle process_queue & input_pkt_queue later.
		*/
		while (!list_empty(&oldsd->poll_list)) {
		struct napi_struct *napi = list_first_entry(&oldsd->poll_list,
		struct napi_struct,
		poll_list);

		list_del_init(&napi->poll_list);
		if (napi->poll == process_backlog)
		napi->state = 0;
		else
		____napi_schedule(sd, napi);
		}

		raise_softirq_irqoff(NET_TX_SOFTIRQ);
		@@ -6029,7 +6039,7 @@ static int dev_cpu_callback(struct notifier_block *nfb,
		netif_rx(skb);
		input_queue_head_incr(oldsd);
		}
		while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
		while ((skb = skb_dequeue(&oldsd->input_pkt_queue))) {
		netif_rx(skb);
		input_queue_head_incr(oldsd);
		}