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/dsa/netlink.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) create mode 100644 net/dsa/netlink.c (limited to 'net/dsa/netlink.c') diff --git a/net/dsa/netlink.c b/net/dsa/netlink.c new file mode 100644 index 000000000..1332e5634 --- /dev/null +++ b/net/dsa/netlink.c @@ -0,0 +1,64 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright 2022 NXP + */ +#include +#include + +#include "netlink.h" +#include "user.h" + +static const struct nla_policy dsa_policy[IFLA_DSA_MAX + 1] = { + [IFLA_DSA_CONDUIT] = { .type = NLA_U32 }, +}; + +static int dsa_changelink(struct net_device *dev, struct nlattr *tb[], + struct nlattr *data[], + struct netlink_ext_ack *extack) +{ + int err; + + if (!data) + return 0; + + if (data[IFLA_DSA_CONDUIT]) { + u32 ifindex = nla_get_u32(data[IFLA_DSA_CONDUIT]); + struct net_device *conduit; + + conduit = __dev_get_by_index(dev_net(dev), ifindex); + if (!conduit) + return -EINVAL; + + err = dsa_user_change_conduit(dev, conduit, extack); + if (err) + return err; + } + + return 0; +} + +static size_t dsa_get_size(const struct net_device *dev) +{ + return nla_total_size(sizeof(u32)) + /* IFLA_DSA_CONDUIT */ + 0; +} + +static int dsa_fill_info(struct sk_buff *skb, const struct net_device *dev) +{ + struct net_device *conduit = dsa_user_to_conduit(dev); + + if (nla_put_u32(skb, IFLA_DSA_CONDUIT, conduit->ifindex)) + return -EMSGSIZE; + + return 0; +} + +struct rtnl_link_ops dsa_link_ops __read_mostly = { + .kind = "dsa", + .priv_size = sizeof(struct dsa_port), + .maxtype = IFLA_DSA_MAX, + .policy = dsa_policy, + .changelink = dsa_changelink, + .get_size = dsa_get_size, + .fill_info = dsa_fill_info, + .netns_refund = true, +}; -- cgit v1.3.1