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/debug_page_alloc.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 mm/debug_page_alloc.c (limited to 'mm/debug_page_alloc.c') diff --git a/mm/debug_page_alloc.c b/mm/debug_page_alloc.c new file mode 100644 index 000000000..fd2664c3c --- /dev/null +++ b/mm/debug_page_alloc.c @@ -0,0 +1,51 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include + +unsigned int _debug_guardpage_minorder; + +bool _debug_pagealloc_enabled_early __read_mostly + = IS_ENABLED(CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT); +EXPORT_SYMBOL(_debug_pagealloc_enabled_early); +DEFINE_STATIC_KEY_FALSE(_debug_pagealloc_enabled); +EXPORT_SYMBOL(_debug_pagealloc_enabled); + +DEFINE_STATIC_KEY_FALSE(_debug_guardpage_enabled); + +static int __init early_debug_pagealloc(char *buf) +{ + return kstrtobool(buf, &_debug_pagealloc_enabled_early); +} +early_param("debug_pagealloc", early_debug_pagealloc); + +static int __init debug_guardpage_minorder_setup(char *buf) +{ + unsigned int res; + + if (!buf || kstrtouint(buf, 10, &res) < 0 || res > MAX_PAGE_ORDER / 2) { + pr_err("Bad debug_guardpage_minorder value: %s\n", buf ?: "(missing)"); + return 0; + } + _debug_guardpage_minorder = res; + pr_info("Setting debug_guardpage_minorder to %u\n", res); + return 0; +} +early_param("debug_guardpage_minorder", debug_guardpage_minorder_setup); + +bool __set_page_guard(struct zone *zone, struct page *page, unsigned int order) +{ + if (order >= debug_guardpage_minorder()) + return false; + + __SetPageGuard(page); + INIT_LIST_HEAD(&page->buddy_list); + set_page_private(page, order); + + return true; +} + +void __clear_page_guard(struct zone *zone, struct page *page, unsigned int order) +{ + __ClearPageGuard(page); + set_page_private(page, 0); +} -- cgit v1.3.1