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/x25/x25_timer.c | 176 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 176 insertions(+) create mode 100644 net/x25/x25_timer.c (limited to 'net/x25/x25_timer.c') diff --git a/net/x25/x25_timer.c b/net/x25/x25_timer.c new file mode 100644 index 000000000..7896cd43f --- /dev/null +++ b/net/x25/x25_timer.c @@ -0,0 +1,176 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * X.25 Packet Layer release 002 + * + * This is ALPHA test software. This code may break your machine, + * randomly fail to work with new releases, misbehave and/or generally + * screw up. It might even work. + * + * This code REQUIRES 2.1.15 or higher + * + * History + * X.25 001 Jonathan Naylor Started coding. + * X.25 002 Jonathan Naylor New timer architecture. + * Centralised disconnection processing. + */ + +#include +#include +#include +#include +#include +#include + +static void x25_heartbeat_expiry(struct timer_list *t); +static void x25_timer_expiry(struct timer_list *t); + +void x25_init_timers(struct sock *sk) +{ + struct x25_sock *x25 = x25_sk(sk); + + timer_setup(&x25->timer, x25_timer_expiry, 0); + + /* initialized by sock_init_data */ + sk->sk_timer.function = x25_heartbeat_expiry; +} + +void x25_start_heartbeat(struct sock *sk) +{ + sk_reset_timer(sk, &sk->sk_timer, jiffies + 5 * HZ); +} + +void x25_stop_heartbeat(struct sock *sk) +{ + sk_stop_timer(sk, &sk->sk_timer); +} + +void x25_start_t2timer(struct sock *sk) +{ + struct x25_sock *x25 = x25_sk(sk); + + sk_reset_timer(sk, &x25->timer, jiffies + x25->t2); +} + +void x25_start_t21timer(struct sock *sk) +{ + struct x25_sock *x25 = x25_sk(sk); + + sk_reset_timer(sk, &x25->timer, jiffies + x25->t21); +} + +void x25_start_t22timer(struct sock *sk) +{ + struct x25_sock *x25 = x25_sk(sk); + + sk_reset_timer(sk, &x25->timer, jiffies + x25->t22); +} + +void x25_start_t23timer(struct sock *sk) +{ + struct x25_sock *x25 = x25_sk(sk); + + sk_reset_timer(sk, &x25->timer, jiffies + x25->t23); +} + +void x25_stop_timer(struct sock *sk) +{ + sk_stop_timer(sk, &x25_sk(sk)->timer); +} + +unsigned long x25_display_timer(struct sock *sk) +{ + struct x25_sock *x25 = x25_sk(sk); + + if (!timer_pending(&x25->timer)) + return 0; + + return x25->timer.expires - jiffies; +} + +static void x25_heartbeat_expiry(struct timer_list *t) +{ + struct sock *sk = timer_container_of(sk, t, sk_timer); + + bh_lock_sock(sk); + if (sock_owned_by_user(sk)) /* can currently only occur in state 3 */ + goto restart_heartbeat; + + switch (x25_sk(sk)->state) { + + case X25_STATE_0: + /* + * Magic here: If we listen() and a new link dies + * before it is accepted() it isn't 'dead' so doesn't + * get removed. + */ + if (sock_flag(sk, SOCK_DESTROY) || + (sk->sk_state == TCP_LISTEN && + sock_flag(sk, SOCK_DEAD))) { + bh_unlock_sock(sk); + x25_destroy_socket_from_timer(sk); + goto out; + } + break; + + case X25_STATE_3: + /* + * Check for the state of the receive buffer. + */ + x25_check_rbuf(sk); + break; + } +restart_heartbeat: + /* Do not rearm once __x25_destroy_socket() has unlinked the socket: + * it is past its cancel point and owns the teardown from there on. + */ + if (sk_hashed(sk)) + x25_start_heartbeat(sk); + bh_unlock_sock(sk); +out: + sock_put(sk); +} + +/* + * Timer has expired, it may have been T2, T21, T22, or T23. We can tell + * by the state machine state. + */ +static inline void x25_do_timer_expiry(struct sock * sk) +{ + struct x25_sock *x25 = x25_sk(sk); + + switch (x25->state) { + + case X25_STATE_3: /* T2 */ + if (x25->condition & X25_COND_ACK_PENDING) { + x25->condition &= ~X25_COND_ACK_PENDING; + x25_enquiry_response(sk); + } + break; + + case X25_STATE_1: /* T21 */ + case X25_STATE_4: /* T22 */ + x25_write_internal(sk, X25_CLEAR_REQUEST); + x25->state = X25_STATE_2; + x25_start_t23timer(sk); + break; + + case X25_STATE_2: /* T23 */ + x25_disconnect(sk, ETIMEDOUT, 0, 0); + break; + } +} + +static void x25_timer_expiry(struct timer_list *t) +{ + struct x25_sock *x25 = timer_container_of(x25, t, timer); + struct sock *sk = &x25->sk; + + bh_lock_sock(sk); + if (sock_owned_by_user(sk)) { /* can currently only occur in state 3 */ + if (x25_sk(sk)->state == X25_STATE_3) + x25_start_t2timer(sk); + } else + x25_do_timer_expiry(sk); + bh_unlock_sock(sk); + sock_put(sk); +} -- cgit v1.3.1