net: link_watch: prevent starvation when processing linkwatch wq

When user has configured a large number of virtual netdev, such
as 4K vlans, the carrier on/off operation of the real netdev
will also cause it's virtual netdev's link state to be processed
in linkwatch. Currently, the processing is done in a work queue,
which may cause rtnl locking starvation problem and worker
starvation problem for other work queue, such as irqfd_inject wq.

This patch releases the cpu when link watch worker has processed
a fixed number of netdev' link watch event, and schedule the
work queue again when there is still link watch event remaining.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/link_watch.c b/net/core/link_watch.c
index 04fdc95357725606f59abec109f1bf2f0a6514fc..f153e060183833a292e1362dc0d7073a65ce6da7 100644 (file)
--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -163,9 +163,16 @@ static void linkwatch_do_dev(struct net_device *dev)
 
 static void __linkwatch_run_queue(int urgent_only)
 {
+#define MAX_DO_DEV_PER_LOOP    100
+
+       int do_dev = MAX_DO_DEV_PER_LOOP;
        struct net_device *dev;
        LIST_HEAD(wrk);
 
+       /* Give urgent case more budget */
+       if (urgent_only)
+               do_dev += MAX_DO_DEV_PER_LOOP;
+
        /*
         * Limit the number of linkwatch events to one
         * per second so that a runaway driver does not
@@ -184,7 +191,7 @@ static void __linkwatch_run_queue(int urgent_only)
        spin_lock_irq(&lweventlist_lock);
        list_splice_init(&lweventlist, &wrk);
 
-       while (!list_empty(&wrk)) {
+       while (!list_empty(&wrk) && do_dev > 0) {
 
                dev = list_first_entry(&wrk, struct net_device, link_watch_list);
                list_del_init(&dev->link_watch_list);
@@ -195,9 +202,13 @@ static void __linkwatch_run_queue(int urgent_only)
                }
                spin_unlock_irq(&lweventlist_lock);
                linkwatch_do_dev(dev);
+               do_dev--;
                spin_lock_irq(&lweventlist_lock);
        }
 
+       /* Add the remaining work back to lweventlist */
+       list_splice_init(&wrk, &lweventlist);
+
        if (!list_empty(&lweventlist))
                linkwatch_schedule_work(0);
        spin_unlock_irq(&lweventlist_lock);