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/devres.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 95 insertions(+) create mode 100644 net/devres.c (limited to 'net/devres.c') diff --git a/net/devres.c b/net/devres.c new file mode 100644 index 000000000..5ccf6ca31 --- /dev/null +++ b/net/devres.c @@ -0,0 +1,95 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * This file contains all networking devres helpers. + */ + +#include +#include +#include + +struct net_device_devres { + struct net_device *ndev; +}; + +static void devm_free_netdev(struct device *dev, void *this) +{ + struct net_device_devres *res = this; + + free_netdev(res->ndev); +} + +struct net_device *devm_alloc_etherdev_mqs(struct device *dev, int sizeof_priv, + unsigned int txqs, unsigned int rxqs) +{ + struct net_device_devres *dr; + + dr = devres_alloc(devm_free_netdev, sizeof(*dr), GFP_KERNEL); + if (!dr) + return NULL; + + dr->ndev = alloc_etherdev_mqs(sizeof_priv, txqs, rxqs); + if (!dr->ndev) { + devres_free(dr); + return NULL; + } + + devres_add(dev, dr); + + return dr->ndev; +} +EXPORT_SYMBOL(devm_alloc_etherdev_mqs); + +static void devm_unregister_netdev(struct device *dev, void *this) +{ + struct net_device_devres *res = this; + + unregister_netdev(res->ndev); +} + +static int netdev_devres_match(struct device *dev, void *this, void *match_data) +{ + struct net_device_devres *res = this; + struct net_device *ndev = match_data; + + return ndev == res->ndev; +} + +/** + * devm_register_netdev - resource managed variant of register_netdev() + * @dev: managing device for this netdev - usually the parent device + * @ndev: device to register + * + * This is a devres variant of register_netdev() for which the unregister + * function will be called automatically when the managing device is + * detached. Note: the net_device used must also be resource managed by + * the same struct device. + */ +int devm_register_netdev(struct device *dev, struct net_device *ndev) +{ + struct net_device_devres *dr; + int ret; + + /* struct net_device must itself be managed. For now a managed netdev + * can only be allocated by devm_alloc_etherdev_mqs() so the check is + * straightforward. + */ + if (WARN_ON(!devres_find(dev, devm_free_netdev, + netdev_devres_match, ndev))) + return -EINVAL; + + dr = devres_alloc(devm_unregister_netdev, sizeof(*dr), GFP_KERNEL); + if (!dr) + return -ENOMEM; + + ret = register_netdev(ndev); + if (ret) { + devres_free(dr); + return ret; + } + + dr->ndev = ndev; + devres_add(ndev->dev.parent, dr); + + return 0; +} +EXPORT_SYMBOL(devm_register_netdev); -- cgit v1.3.1