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 --- include/net/cls_cgroup.h | 88 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 include/net/cls_cgroup.h (limited to 'include/net/cls_cgroup.h') diff --git a/include/net/cls_cgroup.h b/include/net/cls_cgroup.h new file mode 100644 index 000000000..668aeee9b --- /dev/null +++ b/include/net/cls_cgroup.h @@ -0,0 +1,88 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * cls_cgroup.h Control Group Classifier + * + * Authors: Thomas Graf + */ + +#ifndef _NET_CLS_CGROUP_H +#define _NET_CLS_CGROUP_H + +#include +#include +#include +#include +#include + +#ifdef CONFIG_CGROUP_NET_CLASSID +struct cgroup_cls_state { + struct cgroup_subsys_state css; + u32 classid; +}; + +struct cgroup_cls_state *task_cls_state(struct task_struct *p); + +static inline u32 task_cls_classid(struct task_struct *p) +{ + u32 classid; + + if (in_interrupt()) + return 0; + + rcu_read_lock(); + classid = container_of(task_css(p, net_cls_cgrp_id), + struct cgroup_cls_state, css)->classid; + rcu_read_unlock(); + + return classid; +} + +static inline void sock_update_classid(struct sock_cgroup_data *skcd) +{ + u32 classid; + + classid = task_cls_classid(current); + sock_cgroup_set_classid(skcd, classid); +} + +static inline u32 __task_get_classid(struct task_struct *task) +{ + return task_cls_state(task)->classid; +} + +static inline u32 task_get_classid(const struct sk_buff *skb) +{ + u32 classid = __task_get_classid(current); + + /* Due to the nature of the classifier it is required to ignore all + * packets originating from softirq context as accessing `current' + * would lead to false results. + * + * This test assumes that all callers of dev_queue_xmit() explicitly + * disable bh. Knowing this, it is possible to detect softirq based + * calls by looking at the number of nested bh disable calls because + * softirqs always disables bh. + */ + if (softirq_count()) { + struct sock *sk = skb_to_full_sk(skb); + + /* If there is an sock_cgroup_classid we'll use that. */ + if (!sk || !sk_fullsock(sk)) + return 0; + + classid = sock_cgroup_classid(&sk->sk_cgrp_data); + } + + return classid; +} +#else /* !CONFIG_CGROUP_NET_CLASSID */ +static inline void sock_update_classid(struct sock_cgroup_data *skcd) +{ +} + +static inline u32 task_get_classid(const struct sk_buff *skb) +{ + return 0; +} +#endif /* CONFIG_CGROUP_NET_CLASSID */ +#endif /* _NET_CLS_CGROUP_H */ -- cgit v1.3.1