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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.

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
hifive-unleashed-5.1
Eric Dumazet 2015-01-15 17:04:22 -08:00 committed by David S. Miller
parent 57d737c5e2
commit ac64da0b83
1 changed files with 15 additions and 5 deletions
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20
net/core/dev.c
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@ -7072,10 +7072,20 @@ 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);
@ -7086,7 +7096,7 @@ static int dev_cpu_callback(struct notifier_block *nfb,
netif_rx_internal(skb);
input_queue_head_incr(oldsd);
}
while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
while ((skb = skb_dequeue(&oldsd->input_pkt_queue))) {
netif_rx_internal(skb);
input_queue_head_incr(oldsd);
}