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 --- mm/hugetlb_sysctl.c | 145 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 145 insertions(+) create mode 100644 mm/hugetlb_sysctl.c (limited to 'mm/hugetlb_sysctl.c') diff --git a/mm/hugetlb_sysctl.c b/mm/hugetlb_sysctl.c new file mode 100644 index 000000000..e74cf18ad --- /dev/null +++ b/mm/hugetlb_sysctl.c @@ -0,0 +1,145 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * HugeTLB sysfs interfaces. + * (C) Nadia Yvette Chambers, April 2004 + */ + +#include + +#include "hugetlb_internal.h" + +int movable_gigantic_pages; + +#ifdef CONFIG_SYSCTL +static int proc_hugetlb_doulongvec_minmax(const struct ctl_table *table, int write, + void *buffer, size_t *length, + loff_t *ppos, unsigned long *out) +{ + struct ctl_table dup_table; + + /* + * In order to avoid races with __do_proc_doulongvec_minmax(), we + * can duplicate the @table and alter the duplicate of it. + */ + dup_table = *table; + dup_table.data = out; + + return proc_doulongvec_minmax(&dup_table, write, buffer, length, ppos); +} + +static int hugetlb_sysctl_handler_common(bool obey_mempolicy, + const struct ctl_table *table, int write, + void *buffer, size_t *length, loff_t *ppos) +{ + struct hstate *h = &default_hstate; + unsigned long tmp = h->max_huge_pages; + int ret; + + if (!hugepages_supported()) + return -EOPNOTSUPP; + + ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos, + &tmp); + if (ret) + goto out; + + if (write) + ret = __nr_hugepages_store_common(obey_mempolicy, h, + NUMA_NO_NODE, tmp, *length); +out: + return ret; +} + +static int hugetlb_sysctl_handler(const struct ctl_table *table, int write, + void *buffer, size_t *length, loff_t *ppos) +{ + + return hugetlb_sysctl_handler_common(false, table, write, + buffer, length, ppos); +} + +#ifdef CONFIG_NUMA +static int hugetlb_mempolicy_sysctl_handler(const struct ctl_table *table, int write, + void *buffer, size_t *length, loff_t *ppos) +{ + return hugetlb_sysctl_handler_common(true, table, write, + buffer, length, ppos); +} +#endif /* CONFIG_NUMA */ + +static int hugetlb_overcommit_handler(const struct ctl_table *table, int write, + void *buffer, size_t *length, loff_t *ppos) +{ + struct hstate *h = &default_hstate; + unsigned long tmp; + int ret; + + if (!hugepages_supported()) + return -EOPNOTSUPP; + + tmp = h->nr_overcommit_huge_pages; + + if (write && hstate_is_gigantic_no_runtime(h)) + return -EINVAL; + + ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos, + &tmp); + if (ret) + goto out; + + if (write) { + spin_lock_irq(&hugetlb_lock); + h->nr_overcommit_huge_pages = tmp; + spin_unlock_irq(&hugetlb_lock); + } +out: + return ret; +} + +static const struct ctl_table hugetlb_table[] = { + { + .procname = "nr_hugepages", + .data = NULL, + .maxlen = sizeof(unsigned long), + .mode = 0644, + .proc_handler = hugetlb_sysctl_handler, + }, +#ifdef CONFIG_NUMA + { + .procname = "nr_hugepages_mempolicy", + .data = NULL, + .maxlen = sizeof(unsigned long), + .mode = 0644, + .proc_handler = &hugetlb_mempolicy_sysctl_handler, + }, +#endif + { + .procname = "hugetlb_shm_group", + .data = &sysctl_hugetlb_shm_group, + .maxlen = sizeof(gid_t), + .mode = 0644, + .proc_handler = proc_dointvec, + }, + { + .procname = "nr_overcommit_hugepages", + .data = NULL, + .maxlen = sizeof(unsigned long), + .mode = 0644, + .proc_handler = hugetlb_overcommit_handler, + }, +#ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION + { + .procname = "movable_gigantic_pages", + .data = &movable_gigantic_pages, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec, + }, +#endif +}; + +void __init hugetlb_sysctl_init(void) +{ + register_sysctl_init("vm", hugetlb_table); +} +#endif /* CONFIG_SYSCTL */ -- cgit v1.3.1