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/phonet/sysctl.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 95 insertions(+) create mode 100644 net/phonet/sysctl.c (limited to 'net/phonet/sysctl.c') diff --git a/net/phonet/sysctl.c b/net/phonet/sysctl.c new file mode 100644 index 000000000..463a74a27 --- /dev/null +++ b/net/phonet/sysctl.c @@ -0,0 +1,95 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * File: sysctl.c + * + * Phonet /proc/sys/net/phonet interface implementation + * + * Copyright (C) 2008 Nokia Corporation. + * + * Author: Rémi Denis-Courmont + */ + +#include +#include +#include +#include + +#include +#include +#include + +#define DYNAMIC_PORT_MIN 0x40 +#define DYNAMIC_PORT_MAX 0x7f + +static DEFINE_SEQLOCK(local_port_range_lock); +static int local_port_range_min[2] = {0, 0}; +static int local_port_range_max[2] = {1023, 1023}; +static int local_port_range[2] = {DYNAMIC_PORT_MIN, DYNAMIC_PORT_MAX}; +static struct ctl_table_header *phonet_table_hrd; + +static void set_local_port_range(int range[2]) +{ + write_seqlock(&local_port_range_lock); + local_port_range[0] = range[0]; + local_port_range[1] = range[1]; + write_sequnlock(&local_port_range_lock); +} + +void phonet_get_local_port_range(int *min, int *max) +{ + unsigned int seq; + + do { + seq = read_seqbegin(&local_port_range_lock); + if (min) + *min = local_port_range[0]; + if (max) + *max = local_port_range[1]; + } while (read_seqretry(&local_port_range_lock, seq)); +} + +static int proc_local_port_range(const struct ctl_table *table, int write, + void *buffer, size_t *lenp, loff_t *ppos) +{ + int ret; + int range[2] = {local_port_range[0], local_port_range[1]}; + struct ctl_table tmp = { + .data = &range, + .maxlen = sizeof(range), + .mode = table->mode, + .extra1 = &local_port_range_min, + .extra2 = &local_port_range_max, + }; + + ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos); + + if (write && ret == 0) { + if (range[1] < range[0]) + ret = -EINVAL; + else + set_local_port_range(range); + } + + return ret; +} + +static struct ctl_table phonet_table[] = { + { + .procname = "local_port_range", + .data = &local_port_range, + .maxlen = sizeof(local_port_range), + .mode = 0644, + .proc_handler = proc_local_port_range, + }, +}; + +int __init phonet_sysctl_init(void) +{ + phonet_table_hrd = register_net_sysctl(&init_net, "net/phonet", phonet_table); + return phonet_table_hrd == NULL ? -ENOMEM : 0; +} + +void phonet_sysctl_exit(void) +{ + unregister_net_sysctl_table(phonet_table_hrd); +} -- cgit v1.3.1