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_timer.c | 206 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 206 insertions(+) create mode 100644 net/lapb/lapb_timer.c (limited to 'net/lapb/lapb_timer.c') diff --git a/net/lapb/lapb_timer.c b/net/lapb/lapb_timer.c new file mode 100644 index 000000000..9fde6cf20 --- /dev/null +++ b/net/lapb/lapb_timer.c @@ -0,0 +1,206 @@ +// 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 + +static void lapb_t1timer_expiry(struct timer_list *); +static void lapb_t2timer_expiry(struct timer_list *); + +void lapb_start_t1timer(struct lapb_cb *lapb) +{ + timer_delete(&lapb->t1timer); + + lapb->t1timer.function = lapb_t1timer_expiry; + lapb->t1timer.expires = jiffies + lapb->t1; + + lapb->t1timer_running = true; + add_timer(&lapb->t1timer); +} + +void lapb_start_t2timer(struct lapb_cb *lapb) +{ + timer_delete(&lapb->t2timer); + + lapb->t2timer.function = lapb_t2timer_expiry; + lapb->t2timer.expires = jiffies + lapb->t2; + + lapb->t2timer_running = true; + add_timer(&lapb->t2timer); +} + +void lapb_stop_t1timer(struct lapb_cb *lapb) +{ + lapb->t1timer_running = false; + timer_delete(&lapb->t1timer); +} + +void lapb_stop_t2timer(struct lapb_cb *lapb) +{ + lapb->t2timer_running = false; + timer_delete(&lapb->t2timer); +} + +int lapb_t1timer_running(struct lapb_cb *lapb) +{ + return lapb->t1timer_running; +} + +static void lapb_t2timer_expiry(struct timer_list *t) +{ + struct lapb_cb *lapb = timer_container_of(lapb, t, t2timer); + + spin_lock_bh(&lapb->lock); + if (timer_pending(&lapb->t2timer)) /* A new timer has been set up */ + goto out; + if (!lapb->t2timer_running) /* The timer has been stopped */ + goto out; + + if (lapb->condition & LAPB_ACK_PENDING_CONDITION) { + lapb->condition &= ~LAPB_ACK_PENDING_CONDITION; + lapb_timeout_response(lapb); + } + lapb->t2timer_running = false; + +out: + spin_unlock_bh(&lapb->lock); +} + +static void lapb_t1timer_expiry(struct timer_list *t) +{ + struct lapb_cb *lapb = timer_container_of(lapb, t, t1timer); + + spin_lock_bh(&lapb->lock); + if (timer_pending(&lapb->t1timer)) /* A new timer has been set up */ + goto out; + if (!lapb->t1timer_running) /* The timer has been stopped */ + goto out; + + switch (lapb->state) { + + /* + * If we are a DCE, send DM up to N2 times, then switch to + * STATE_1 and send SABM(E). + */ + case LAPB_STATE_0: + if (lapb->mode & LAPB_DCE && + lapb->n2count != lapb->n2) { + lapb->n2count++; + lapb_send_control(lapb, LAPB_DM, LAPB_POLLOFF, LAPB_RESPONSE); + } else { + lapb->state = LAPB_STATE_1; + lapb_establish_data_link(lapb); + } + break; + + /* + * Awaiting connection state, send SABM(E), up to N2 times. + */ + case LAPB_STATE_1: + if (lapb->n2count == lapb->n2) { + lapb_clear_queues(lapb); + lapb->state = LAPB_STATE_0; + lapb_disconnect_indication(lapb, LAPB_TIMEDOUT); + lapb_dbg(0, "(%p) S1 -> S0\n", lapb->dev); + lapb->t1timer_running = false; + goto out; + } else { + lapb->n2count++; + if (lapb->mode & LAPB_EXTENDED) { + lapb_dbg(1, "(%p) S1 TX SABME(1)\n", + lapb->dev); + lapb_send_control(lapb, LAPB_SABME, LAPB_POLLON, LAPB_COMMAND); + } else { + lapb_dbg(1, "(%p) S1 TX SABM(1)\n", + lapb->dev); + lapb_send_control(lapb, LAPB_SABM, LAPB_POLLON, LAPB_COMMAND); + } + } + break; + + /* + * Awaiting disconnection state, send DISC, up to N2 times. + */ + case LAPB_STATE_2: + if (lapb->n2count == lapb->n2) { + lapb_clear_queues(lapb); + lapb->state = LAPB_STATE_0; + lapb_disconnect_confirmation(lapb, LAPB_TIMEDOUT); + lapb_dbg(0, "(%p) S2 -> S0\n", lapb->dev); + lapb->t1timer_running = false; + goto out; + } else { + lapb->n2count++; + lapb_dbg(1, "(%p) S2 TX DISC(1)\n", lapb->dev); + lapb_send_control(lapb, LAPB_DISC, LAPB_POLLON, LAPB_COMMAND); + } + break; + + /* + * Data transfer state, restransmit I frames, up to N2 times. + */ + case LAPB_STATE_3: + if (lapb->n2count == lapb->n2) { + lapb_clear_queues(lapb); + lapb->state = LAPB_STATE_0; + lapb_stop_t2timer(lapb); + lapb_disconnect_indication(lapb, LAPB_TIMEDOUT); + lapb_dbg(0, "(%p) S3 -> S0\n", lapb->dev); + lapb->t1timer_running = false; + goto out; + } else { + lapb->n2count++; + lapb_requeue_frames(lapb); + lapb_kick(lapb); + } + break; + + /* + * Frame reject state, restransmit FRMR frames, up to N2 times. + */ + case LAPB_STATE_4: + if (lapb->n2count == lapb->n2) { + lapb_clear_queues(lapb); + lapb->state = LAPB_STATE_0; + lapb_disconnect_indication(lapb, LAPB_TIMEDOUT); + lapb_dbg(0, "(%p) S4 -> S0\n", lapb->dev); + lapb->t1timer_running = false; + goto out; + } else { + lapb->n2count++; + lapb_transmit_frmr(lapb); + } + break; + } + + lapb_start_t1timer(lapb); + +out: + spin_unlock_bh(&lapb->lock); +} -- cgit v1.3.1