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/lapb/lapb_out.c | 205 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 205 insertions(+) create mode 100644 net/lapb/lapb_out.c (limited to 'net/lapb/lapb_out.c') diff --git a/net/lapb/lapb_out.c b/net/lapb/lapb_out.c new file mode 100644 index 000000000..a966d29c7 --- /dev/null +++ b/net/lapb/lapb_out.c @@ -0,0 +1,205 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * LAPB release 002 + * + * This code REQUIRES 2.1.15 or higher/ NET3.038 + * + * History + * LAPB 001 Jonathan Naylor Started Coding + * LAPB 002 Jonathan Naylor New timer architecture. + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* + * This procedure is passed a buffer descriptor for an iframe. It builds + * the rest of the control part of the frame and then writes it out. + */ +static void lapb_send_iframe(struct lapb_cb *lapb, struct sk_buff *skb, int poll_bit) +{ + unsigned char *frame; + + if (!skb) + return; + + if (lapb->mode & LAPB_EXTENDED) { + frame = skb_push(skb, 2); + + frame[0] = LAPB_I; + frame[0] |= lapb->vs << 1; + frame[1] = poll_bit ? LAPB_EPF : 0; + frame[1] |= lapb->vr << 1; + } else { + frame = skb_push(skb, 1); + + *frame = LAPB_I; + *frame |= poll_bit ? LAPB_SPF : 0; + *frame |= lapb->vr << 5; + *frame |= lapb->vs << 1; + } + + lapb_dbg(1, "(%p) S%d TX I(%d) S%d R%d\n", + lapb->dev, lapb->state, poll_bit, lapb->vs, lapb->vr); + + lapb_transmit_buffer(lapb, skb, LAPB_COMMAND); +} + +void lapb_kick(struct lapb_cb *lapb) +{ + struct sk_buff *skb, *skbn; + unsigned short modulus, start, end; + + modulus = (lapb->mode & LAPB_EXTENDED) ? LAPB_EMODULUS : LAPB_SMODULUS; + start = !skb_peek(&lapb->ack_queue) ? lapb->va : lapb->vs; + end = (lapb->va + lapb->window) % modulus; + + if (!(lapb->condition & LAPB_PEER_RX_BUSY_CONDITION) && + start != end && skb_peek(&lapb->write_queue)) { + lapb->vs = start; + + /* + * Dequeue the frame and copy it. + */ + skb = skb_dequeue(&lapb->write_queue); + + do { + skbn = skb_copy(skb, GFP_ATOMIC); + if (!skbn) { + skb_queue_head(&lapb->write_queue, skb); + break; + } + + if (skb->sk) + skb_set_owner_w(skbn, skb->sk); + + /* + * Transmit the frame copy. + */ + lapb_send_iframe(lapb, skbn, LAPB_POLLOFF); + + lapb->vs = (lapb->vs + 1) % modulus; + + /* + * Requeue the original data frame. + */ + skb_queue_tail(&lapb->ack_queue, skb); + + } while (lapb->vs != end && (skb = skb_dequeue(&lapb->write_queue)) != NULL); + + lapb->condition &= ~LAPB_ACK_PENDING_CONDITION; + + if (!lapb_t1timer_running(lapb)) + lapb_start_t1timer(lapb); + } +} + +void lapb_transmit_buffer(struct lapb_cb *lapb, struct sk_buff *skb, int type) +{ + unsigned char *ptr; + + ptr = skb_push(skb, 1); + + if (lapb->mode & LAPB_MLP) { + if (lapb->mode & LAPB_DCE) { + if (type == LAPB_COMMAND) + *ptr = LAPB_ADDR_C; + if (type == LAPB_RESPONSE) + *ptr = LAPB_ADDR_D; + } else { + if (type == LAPB_COMMAND) + *ptr = LAPB_ADDR_D; + if (type == LAPB_RESPONSE) + *ptr = LAPB_ADDR_C; + } + } else { + if (lapb->mode & LAPB_DCE) { + if (type == LAPB_COMMAND) + *ptr = LAPB_ADDR_A; + if (type == LAPB_RESPONSE) + *ptr = LAPB_ADDR_B; + } else { + if (type == LAPB_COMMAND) + *ptr = LAPB_ADDR_B; + if (type == LAPB_RESPONSE) + *ptr = LAPB_ADDR_A; + } + } + + lapb_dbg(2, "(%p) S%d TX %3ph\n", lapb->dev, lapb->state, skb->data); + + if (!lapb_data_transmit(lapb, skb)) + kfree_skb(skb); +} + +void lapb_establish_data_link(struct lapb_cb *lapb) +{ + lapb->condition = 0x00; + lapb->n2count = 0; + + if (lapb->mode & LAPB_EXTENDED) { + lapb_dbg(1, "(%p) S%d TX SABME(1)\n", lapb->dev, lapb->state); + lapb_send_control(lapb, LAPB_SABME, LAPB_POLLON, LAPB_COMMAND); + } else { + lapb_dbg(1, "(%p) S%d TX SABM(1)\n", lapb->dev, lapb->state); + lapb_send_control(lapb, LAPB_SABM, LAPB_POLLON, LAPB_COMMAND); + } + + lapb_start_t1timer(lapb); + lapb_stop_t2timer(lapb); +} + +void lapb_enquiry_response(struct lapb_cb *lapb) +{ + lapb_dbg(1, "(%p) S%d TX RR(1) R%d\n", + lapb->dev, lapb->state, lapb->vr); + + lapb_send_control(lapb, LAPB_RR, LAPB_POLLON, LAPB_RESPONSE); + + lapb->condition &= ~LAPB_ACK_PENDING_CONDITION; +} + +void lapb_timeout_response(struct lapb_cb *lapb) +{ + lapb_dbg(1, "(%p) S%d TX RR(0) R%d\n", + lapb->dev, lapb->state, lapb->vr); + lapb_send_control(lapb, LAPB_RR, LAPB_POLLOFF, LAPB_RESPONSE); + + lapb->condition &= ~LAPB_ACK_PENDING_CONDITION; +} + +void lapb_check_iframes_acked(struct lapb_cb *lapb, unsigned short nr) +{ + if (lapb->vs == nr) { + lapb_frames_acked(lapb, nr); + lapb_stop_t1timer(lapb); + lapb->n2count = 0; + } else if (lapb->va != nr) { + lapb_frames_acked(lapb, nr); + lapb_start_t1timer(lapb); + } +} + +void lapb_check_need_response(struct lapb_cb *lapb, int type, int pf) +{ + if (type == LAPB_COMMAND && pf) + lapb_enquiry_response(lapb); +} -- cgit v1.3.1