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/dsa/user.h | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 71 insertions(+) create mode 100644 net/dsa/user.h (limited to 'net/dsa/user.h') diff --git a/net/dsa/user.h b/net/dsa/user.h new file mode 100644 index 000000000..016884bea --- /dev/null +++ b/net/dsa/user.h @@ -0,0 +1,71 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ + +#ifndef __DSA_USER_H +#define __DSA_USER_H + +#include +#include +#include +#include +#include +#include +#include + +struct net_device; +struct netlink_ext_ack; + +extern struct notifier_block dsa_user_switchdev_notifier; +extern struct notifier_block dsa_user_switchdev_blocking_notifier; + +struct dsa_user_priv { + /* Copy of CPU port xmit for faster access in user transmit hot path */ + struct sk_buff * (*xmit)(struct sk_buff *skb, + struct net_device *dev); + + struct gro_cells gcells; + + /* DSA port data, such as switch, port index, etc. */ + struct dsa_port *dp; + +#ifdef CONFIG_NET_POLL_CONTROLLER + struct netpoll *netpoll; +#endif + + /* TC context */ + struct list_head mall_tc_list; +}; + +void dsa_user_mii_bus_init(struct dsa_switch *ds); +int dsa_user_create(struct dsa_port *dp); +void dsa_user_destroy(struct net_device *user_dev); +int dsa_user_suspend(struct net_device *user_dev); +int dsa_user_resume(struct net_device *user_dev); +int dsa_user_register_notifier(void); +void dsa_user_unregister_notifier(void); +int dsa_user_host_uc_install(struct net_device *dev, const u8 *addr); +void dsa_user_host_uc_uninstall(struct net_device *dev); +void dsa_user_sync_ha(struct net_device *dev); +void dsa_user_unsync_ha(struct net_device *dev); +void dsa_user_setup_tagger(struct net_device *user); +int dsa_user_change_mtu(struct net_device *dev, int new_mtu); +int dsa_user_change_conduit(struct net_device *dev, struct net_device *conduit, + struct netlink_ext_ack *extack); +int dsa_user_manage_vlan_filtering(struct net_device *dev, + bool vlan_filtering); + +static inline struct dsa_port *dsa_user_to_port(const struct net_device *dev) +{ + struct dsa_user_priv *p = netdev_priv(dev); + + return p->dp; +} + +static inline struct net_device * +dsa_user_to_conduit(const struct net_device *dev) +{ + struct dsa_port *dp = dsa_user_to_port(dev); + + return dsa_port_to_conduit(dp); +} + +#endif -- cgit v1.3.1