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 --- drivers/mtd/chips/chipreg.c | 102 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 102 insertions(+) create mode 100644 drivers/mtd/chips/chipreg.c (limited to 'drivers/mtd/chips/chipreg.c') diff --git a/drivers/mtd/chips/chipreg.c b/drivers/mtd/chips/chipreg.c new file mode 100644 index 000000000..a05e10368 --- /dev/null +++ b/drivers/mtd/chips/chipreg.c @@ -0,0 +1,102 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Registration for chip drivers + * + */ + +#include +#include +#include +#include +#include +#include +#include + +static DEFINE_SPINLOCK(chip_drvs_lock); +static LIST_HEAD(chip_drvs_list); + +void register_mtd_chip_driver(struct mtd_chip_driver *drv) +{ + spin_lock(&chip_drvs_lock); + list_add(&drv->list, &chip_drvs_list); + spin_unlock(&chip_drvs_lock); +} + +void unregister_mtd_chip_driver(struct mtd_chip_driver *drv) +{ + spin_lock(&chip_drvs_lock); + list_del(&drv->list); + spin_unlock(&chip_drvs_lock); +} + +static struct mtd_chip_driver *get_mtd_chip_driver (const char *name) +{ + struct mtd_chip_driver *ret = NULL, *this; + + spin_lock(&chip_drvs_lock); + + list_for_each_entry(this, &chip_drvs_list, list) { + if (!strcmp(this->name, name)) { + ret = this; + break; + } + } + if (ret && !try_module_get(ret->module)) + ret = NULL; + + spin_unlock(&chip_drvs_lock); + + return ret; +} + + /* Hide all the horrid details, like some silly person taking + get_module_symbol() away from us, from the caller. */ + +struct mtd_info *do_map_probe(const char *name, struct map_info *map) +{ + struct mtd_chip_driver *drv; + struct mtd_info *ret; + + drv = get_mtd_chip_driver(name); + + if (!drv && !request_module("%s", name)) + drv = get_mtd_chip_driver(name); + + if (!drv) + return NULL; + + ret = drv->probe(map); + + /* We decrease the use count here. It may have been a + probe-only module, which is no longer required from this + point, having given us a handle on (and increased the use + count of) the actual driver code. + */ + module_put(drv->module); + + return ret; +} +/* + * Destroy an MTD device which was created for a map device. + * Make sure the MTD device is already unregistered before calling this + */ +void map_destroy(struct mtd_info *mtd) +{ + struct map_info *map = mtd->priv; + + if (map->fldrv->destroy) + map->fldrv->destroy(mtd); + + module_put(map->fldrv->module); + + kfree(mtd); +} + +EXPORT_SYMBOL(register_mtd_chip_driver); +EXPORT_SYMBOL(unregister_mtd_chip_driver); +EXPORT_SYMBOL(do_map_probe); +EXPORT_SYMBOL(map_destroy); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("David Woodhouse "); +MODULE_DESCRIPTION("Core routines for registering and invoking MTD chip drivers"); -- cgit v1.3.1