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/kunit/device.h | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) create mode 100644 include/kunit/device.h (limited to 'include/kunit/device.h') diff --git a/include/kunit/device.h b/include/kunit/device.h new file mode 100644 index 000000000..2450110ad --- /dev/null +++ b/include/kunit/device.h @@ -0,0 +1,80 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * KUnit basic device implementation + * + * Helpers for creating and managing fake devices for KUnit tests. + * + * Copyright (C) 2023, Google LLC. + * Author: David Gow + */ + +#ifndef _KUNIT_DEVICE_H +#define _KUNIT_DEVICE_H + +#if IS_ENABLED(CONFIG_KUNIT) + +#include + +struct device; +struct device_driver; + +/** + * kunit_driver_create() - Create a struct device_driver attached to the kunit_bus + * @test: The test context object. + * @name: The name to give the created driver. + * + * Creates a struct device_driver attached to the kunit_bus, with the name @name. + * This driver will automatically be cleaned up on test exit. + * + * Return: a stub struct device_driver, managed by KUnit, with the name @name. + */ +struct device_driver *kunit_driver_create(struct kunit *test, const char *name); + +/** + * kunit_device_register() - Create a struct device for use in KUnit tests + * @test: The test context object. + * @name: The name to give the created device. + * + * Creates a struct kunit_device (which is a struct device) with the given name, + * and a corresponding driver. The device and driver will be cleaned up on test + * exit, or when kunit_device_unregister is called. See also + * kunit_device_register_with_driver, if you wish to provide your own + * struct device_driver. + * + * Return: a pointer to a struct device which will be cleaned up when the test + * exits, or an error pointer if the device could not be allocated or registered. + */ +struct device *kunit_device_register(struct kunit *test, const char *name); + +/** + * kunit_device_register_with_driver() - Create a struct device for use in KUnit tests + * @test: The test context object. + * @name: The name to give the created device. + * @drv: The struct device_driver to associate with the device. + * + * Creates a struct kunit_device (which is a struct device) with the given + * name, and driver. The device will be cleaned up on test exit, or when + * kunit_device_unregister is called. See also kunit_device_register, if you + * wish KUnit to create and manage a driver for you. + * + * Return: a pointer to a struct device which will be cleaned up when the test + * exits, or an error pointer if the device could not be allocated or registered. + */ +struct device *kunit_device_register_with_driver(struct kunit *test, + const char *name, + const struct device_driver *drv); + +/** + * kunit_device_unregister() - Unregister a KUnit-managed device + * @test: The test context object which created the device + * @dev: The device. + * + * Unregisters and destroys a struct device which was created with + * kunit_device_register or kunit_device_register_with_driver. If KUnit created + * a driver, cleans it up as well. + */ +void kunit_device_unregister(struct kunit *test, struct device *dev); + +#endif + +#endif -- cgit v1.3.1