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/atm/raw.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 net/atm/raw.c (limited to 'net/atm/raw.c') diff --git a/net/atm/raw.c b/net/atm/raw.c new file mode 100644 index 000000000..87d136c75 --- /dev/null +++ b/net/atm/raw.c @@ -0,0 +1,75 @@ +// SPDX-License-Identifier: GPL-2.0 +/* net/atm/raw.c - Raw AAL0 and AAL5 transports */ + +/* Written 1995-2000 by Werner Almesberger, EPFL LRC/ICA */ + +#define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__ + +#include +#include +#include +#include +#include +#include +#include + +#include "common.h" +#include "protocols.h" + +/* + * SKB == NULL indicates that the link is being closed + */ + +static void atm_push_raw(struct atm_vcc *vcc, struct sk_buff *skb) +{ + if (skb) { + struct sock *sk = sk_atm(vcc); + + skb_queue_tail(&sk->sk_receive_queue, skb); + sk->sk_data_ready(sk); + } +} + +static void atm_pop_raw(struct atm_vcc *vcc, struct sk_buff *skb) +{ + struct sock *sk = sk_atm(vcc); + + pr_debug("(%d) %d -= %d\n", + vcc->vci, sk_wmem_alloc_get(sk), ATM_SKB(skb)->acct_truesize); + atm_return_tx(vcc, skb); + dev_kfree_skb_any(skb); + sk->sk_write_space(sk); +} + +static int atm_send_aal0(struct atm_vcc *vcc, struct sk_buff *skb) +{ + /* + * Note that if vpi/vci are _ANY or _UNSPEC the below will + * still work + */ + if (!capable(CAP_NET_ADMIN) && + (((u32 *)skb->data)[0] & (ATM_HDR_VPI_MASK | ATM_HDR_VCI_MASK)) != + ((vcc->vpi << ATM_HDR_VPI_SHIFT) | + (vcc->vci << ATM_HDR_VCI_SHIFT))) { + kfree_skb(skb); + return -EADDRNOTAVAIL; + } + return vcc->dev->ops->send(vcc, skb); +} + +int atm_init_aal0(struct atm_vcc *vcc) +{ + vcc->push = atm_push_raw; + vcc->pop = atm_pop_raw; + vcc->send = atm_send_aal0; + return 0; +} + +int atm_init_aal5(struct atm_vcc *vcc) +{ + vcc->push = atm_push_raw; + vcc->pop = atm_pop_raw; + vcc->send = vcc->dev->ops->send; + return 0; +} +EXPORT_SYMBOL(atm_init_aal5); -- cgit v1.3.1