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/mctp/test/utils.h | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 net/mctp/test/utils.h (limited to 'net/mctp/test/utils.h') diff --git a/net/mctp/test/utils.h b/net/mctp/test/utils.h new file mode 100644 index 000000000..47603732e --- /dev/null +++ b/net/mctp/test/utils.h @@ -0,0 +1,75 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef __NET_MCTP_TEST_UTILS_H +#define __NET_MCTP_TEST_UTILS_H + +#include + +#include +#include + +#include + +#define MCTP_DEV_TEST_MTU 68 + +struct mctp_test_dev { + struct net_device *ndev; + struct mctp_dev *mdev; + + unsigned short lladdr_len; + unsigned char lladdr[MAX_ADDR_LEN]; + + struct sk_buff_head pkts; +}; + +struct mctp_test_dev; + +struct mctp_test_route { + struct mctp_route rt; +}; + +struct mctp_test_bind_setup { + mctp_eid_t bind_addr; + int bind_net; + u8 bind_type; + + bool have_peer; + mctp_eid_t peer_addr; + int peer_net; + + /* optional name. Used for comparison in "lookup" tests */ + const char *name; +}; + +struct mctp_test_dev *mctp_test_create_dev(void); +struct mctp_test_dev *mctp_test_create_dev_with_addr(mctp_eid_t eid); +struct mctp_test_dev *mctp_test_create_dev_lladdr(unsigned short lladdr_len, + const unsigned char *lladdr); +void mctp_test_destroy_dev(struct mctp_test_dev *dev); + +struct mctp_test_route *mctp_test_create_route_direct(struct net *net, + struct mctp_dev *dev, + mctp_eid_t eid, + unsigned int mtu); +struct mctp_test_route *mctp_test_create_route_gw(struct net *net, + unsigned int netid, + mctp_eid_t eid, + mctp_eid_t gw, + unsigned int mtu); +void mctp_test_dst_setup(struct kunit *test, struct mctp_dst *dst, + struct mctp_test_dev *dev, unsigned int mtu); +void mctp_test_route_destroy(struct kunit *test, struct mctp_test_route *rt); +void mctp_test_skb_set_dev(struct sk_buff *skb, struct mctp_test_dev *dev); +struct sk_buff *mctp_test_create_skb(const struct mctp_hdr *hdr, + unsigned int data_len); +struct sk_buff *__mctp_test_create_skb_data(const struct mctp_hdr *hdr, + const void *data, size_t data_len); + +#define mctp_test_create_skb_data(h, d) \ + __mctp_test_create_skb_data(h, d, sizeof(*d)) + +void mctp_test_bind_run(struct kunit *test, + const struct mctp_test_bind_setup *setup, + int *ret_bind_errno, struct socket **sock); + +#endif /* __NET_MCTP_TEST_UTILS_H */ -- cgit v1.3.1