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/ppp/pppox.c | 172 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 172 insertions(+) create mode 100644 drivers/net/ppp/pppox.c (limited to 'drivers/net/ppp/pppox.c') diff --git a/drivers/net/ppp/pppox.c b/drivers/net/ppp/pppox.c new file mode 100644 index 000000000..a6f72c813 --- /dev/null +++ b/drivers/net/ppp/pppox.c @@ -0,0 +1,172 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/** -*- linux-c -*- *********************************************************** + * Linux PPP over X/Ethernet (PPPoX/PPPoE) Sockets + * + * PPPoX --- Generic PPP encapsulation socket family + * PPPoE --- PPP over Ethernet (RFC 2516) + * + * Version: 0.5.2 + * + * Author: Michal Ostrowski + * + * 051000 : Initialization cleanup + * + * License: + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#include + +static const struct pppox_proto *pppox_protos[PX_MAX_PROTO + 1]; + +int register_pppox_proto(int proto_num, const struct pppox_proto *pp) +{ + if (proto_num < 0 || proto_num > PX_MAX_PROTO) + return -EINVAL; + if (pppox_protos[proto_num]) + return -EALREADY; + pppox_protos[proto_num] = pp; + return 0; +} + +void unregister_pppox_proto(int proto_num) +{ + if (proto_num >= 0 && proto_num <= PX_MAX_PROTO) + pppox_protos[proto_num] = NULL; +} + +void pppox_unbind_sock(struct sock *sk) +{ + /* Clear connection to ppp device, if attached. */ + + if (sk->sk_state & (PPPOX_BOUND | PPPOX_CONNECTED)) { + ppp_unregister_channel(&pppox_sk(sk)->chan); + sk->sk_state = PPPOX_DEAD; + } +} + +EXPORT_SYMBOL(register_pppox_proto); +EXPORT_SYMBOL(unregister_pppox_proto); +EXPORT_SYMBOL(pppox_unbind_sock); + +int pppox_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg) +{ + struct sock *sk = sock->sk; + struct pppox_sock *po = pppox_sk(sk); + int rc; + + lock_sock(sk); + + switch (cmd) { + case PPPIOCGCHAN: { + struct sk_buff *skb; + int index; + + rc = -ENOTCONN; + if (!(sk->sk_state & PPPOX_CONNECTED)) + break; + + rc = -EINVAL; + index = ppp_channel_index(&po->chan); + if (put_user(index , (int __user *) arg)) + break; + + rc = 0; + /* PPPIOCGCHAN historically marks the userspace handoff to + * generic PPP; pppd then attaches the returned channel to + * /dev/ppp. + */ + sk->sk_state |= PPPOX_BOUND; + /* Let lockless receive paths finish queueing against the old + * state. + */ + synchronize_net(); + /* Drain packets queued before the handoff because a bound + * socket is no longer readable. + */ + while ((skb = skb_dequeue(&sk->sk_receive_queue))) { + skb_orphan(skb); + ppp_input(&po->chan, skb); + } + break; + } + default: + rc = pppox_protos[sk->sk_protocol]->ioctl ? + pppox_protos[sk->sk_protocol]->ioctl(sock, cmd, arg) : -ENOTTY; + } + + release_sock(sk); + return rc; +} + +EXPORT_SYMBOL(pppox_ioctl); + +#ifdef CONFIG_COMPAT +int pppox_compat_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg) +{ + return pppox_ioctl(sock, cmd, (unsigned long)compat_ptr(arg)); +} + +EXPORT_SYMBOL(pppox_compat_ioctl); +#endif + +static int pppox_create(struct net *net, struct socket *sock, int protocol, + int kern) +{ + int rc = -EPROTOTYPE; + + if (protocol < 0 || protocol > PX_MAX_PROTO) + goto out; + + rc = -EPROTONOSUPPORT; + if (!pppox_protos[protocol]) + request_module("net-pf-%d-proto-%d", PF_PPPOX, protocol); + if (!pppox_protos[protocol] || + !try_module_get(pppox_protos[protocol]->owner)) + goto out; + + rc = pppox_protos[protocol]->create(net, sock, kern); + + module_put(pppox_protos[protocol]->owner); +out: + return rc; +} + +static const struct net_proto_family pppox_proto_family = { + .family = PF_PPPOX, + .create = pppox_create, + .owner = THIS_MODULE, +}; + +static int __init pppox_init(void) +{ + return sock_register(&pppox_proto_family); +} + +static void __exit pppox_exit(void) +{ + sock_unregister(PF_PPPOX); +} + +module_init(pppox_init); +module_exit(pppox_exit); + +MODULE_AUTHOR("Michal Ostrowski "); +MODULE_DESCRIPTION("PPP over Ethernet driver (generic socket layer)"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS_NETPROTO(PF_PPPOX); -- cgit v1.3.1