From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- net/openvswitch/dp_notify.c | 86 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) create mode 100644 net/openvswitch/dp_notify.c (limited to 'net/openvswitch/dp_notify.c') diff --git a/net/openvswitch/dp_notify.c b/net/openvswitch/dp_notify.c new file mode 100644 index 000000000..a2af90ee9 --- /dev/null +++ b/net/openvswitch/dp_notify.c @@ -0,0 +1,86 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (c) 2007-2012 Nicira, Inc. + */ + +#include +#include +#include + +#include "datapath.h" +#include "vport-internal_dev.h" +#include "vport-netdev.h" + +static void dp_detach_port_notify(struct vport *vport) +{ + struct sk_buff *notify; + struct datapath *dp; + + dp = vport->dp; + notify = ovs_vport_cmd_build_info(vport, ovs_dp_get_net(dp), + 0, 0, OVS_VPORT_CMD_DEL); + ovs_dp_detach_port(vport); + if (IS_ERR(notify)) { + genl_set_err(&dp_vport_genl_family, ovs_dp_get_net(dp), 0, + 0, PTR_ERR(notify)); + return; + } + + genlmsg_multicast_netns(&dp_vport_genl_family, + ovs_dp_get_net(dp), notify, 0, + 0, GFP_KERNEL); +} + +void ovs_dp_notify_wq(struct work_struct *work) +{ + struct ovs_net *ovs_net = container_of(work, struct ovs_net, dp_notify_work); + struct datapath *dp; + + ovs_lock(); + list_for_each_entry(dp, &ovs_net->dps, list_node) { + int i; + + for (i = 0; i < DP_VPORT_HASH_BUCKETS; i++) { + struct vport *vport; + struct hlist_node *n; + + hlist_for_each_entry_safe(vport, n, &dp->ports[i], dp_hash_node) { + if (vport->ops->type == OVS_VPORT_TYPE_INTERNAL) + continue; + + if (!(netif_is_ovs_port(vport->dev))) + dp_detach_port_notify(vport); + } + } + } + ovs_unlock(); +} + +static int dp_device_event(struct notifier_block *unused, unsigned long event, + void *ptr) +{ + struct ovs_net *ovs_net; + struct net_device *dev = netdev_notifier_info_to_dev(ptr); + struct vport *vport = NULL; + + if (!ovs_is_internal_dev(dev)) + vport = ovs_netdev_get_vport(dev); + + if (!vport) + return NOTIFY_DONE; + + if (event == NETDEV_UNREGISTER) { + /* upper_dev_unlink and decrement promisc immediately */ + ovs_netdev_detach_dev(vport); + + /* schedule vport destroy, dev_put and genl notification */ + ovs_net = net_generic(dev_net(dev), ovs_net_id); + queue_work(system_percpu_wq, &ovs_net->dp_notify_work); + } + + return NOTIFY_DONE; +} + +struct notifier_block ovs_dp_device_notifier = { + .notifier_call = dp_device_event +}; -- cgit v1.3.1