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/net/wireguard/queueing.c | 109 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 109 insertions(+) create mode 100644 drivers/net/wireguard/queueing.c (limited to 'drivers/net/wireguard/queueing.c') diff --git a/drivers/net/wireguard/queueing.c b/drivers/net/wireguard/queueing.c new file mode 100644 index 000000000..26d235d15 --- /dev/null +++ b/drivers/net/wireguard/queueing.c @@ -0,0 +1,109 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2015-2019 Jason A. Donenfeld . All Rights Reserved. + */ + +#include "queueing.h" +#include + +struct multicore_worker __percpu * +wg_packet_percpu_multicore_worker_alloc(work_func_t function, void *ptr) +{ + int cpu; + struct multicore_worker __percpu *worker = alloc_percpu(struct multicore_worker); + + if (!worker) + return NULL; + + for_each_possible_cpu(cpu) { + per_cpu_ptr(worker, cpu)->ptr = ptr; + INIT_WORK(&per_cpu_ptr(worker, cpu)->work, function); + } + return worker; +} + +int wg_packet_queue_init(struct crypt_queue *queue, work_func_t function, + unsigned int len) +{ + int ret; + + memset(queue, 0, sizeof(*queue)); + queue->last_cpu = -1; + ret = ptr_ring_init(&queue->ring, len, GFP_KERNEL); + if (ret) + return ret; + queue->worker = wg_packet_percpu_multicore_worker_alloc(function, queue); + if (!queue->worker) { + ptr_ring_cleanup(&queue->ring, NULL); + return -ENOMEM; + } + return 0; +} + +void wg_packet_queue_free(struct crypt_queue *queue, bool purge) +{ + free_percpu(queue->worker); + WARN_ON(!purge && !__ptr_ring_empty(&queue->ring)); + ptr_ring_cleanup(&queue->ring, purge ? __skb_array_destroy_skb : NULL); +} + +#define NEXT(skb) ((skb)->prev) +#define STUB(queue) ((struct sk_buff *)&queue->empty) + +void wg_prev_queue_init(struct prev_queue *queue) +{ + NEXT(STUB(queue)) = NULL; + queue->head = queue->tail = STUB(queue); + queue->peeked = NULL; + atomic_set(&queue->count, 0); + BUILD_BUG_ON( + offsetof(struct sk_buff, next) != offsetof(struct prev_queue, empty.next) - + offsetof(struct prev_queue, empty) || + offsetof(struct sk_buff, prev) != offsetof(struct prev_queue, empty.prev) - + offsetof(struct prev_queue, empty)); +} + +static void __wg_prev_queue_enqueue(struct prev_queue *queue, struct sk_buff *skb) +{ + WRITE_ONCE(NEXT(skb), NULL); + WRITE_ONCE(NEXT(xchg_release(&queue->head, skb)), skb); +} + +bool wg_prev_queue_enqueue(struct prev_queue *queue, struct sk_buff *skb) +{ + if (!atomic_add_unless(&queue->count, 1, MAX_QUEUED_PACKETS)) + return false; + __wg_prev_queue_enqueue(queue, skb); + return true; +} + +struct sk_buff *wg_prev_queue_dequeue(struct prev_queue *queue) +{ + struct sk_buff *tail = queue->tail, *next = smp_load_acquire(&NEXT(tail)); + + if (tail == STUB(queue)) { + if (!next) + return NULL; + queue->tail = next; + tail = next; + next = smp_load_acquire(&NEXT(next)); + } + if (next) { + queue->tail = next; + atomic_dec(&queue->count); + return tail; + } + if (tail != READ_ONCE(queue->head)) + return NULL; + __wg_prev_queue_enqueue(queue, STUB(queue)); + next = smp_load_acquire(&NEXT(tail)); + if (next) { + queue->tail = next; + atomic_dec(&queue->count); + return tail; + } + return NULL; +} + +#undef NEXT +#undef STUB -- cgit v1.3.1