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/batman-adv/bitarray.h | 56 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 net/batman-adv/bitarray.h (limited to 'net/batman-adv/bitarray.h') diff --git a/net/batman-adv/bitarray.h b/net/batman-adv/bitarray.h new file mode 100644 index 000000000..2b9f5dbb3 --- /dev/null +++ b/net/batman-adv/bitarray.h @@ -0,0 +1,56 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (C) B.A.T.M.A.N. contributors: + * + * Simon Wunderlich, Marek Lindner + */ + +#ifndef _NET_BATMAN_ADV_BITARRAY_H_ +#define _NET_BATMAN_ADV_BITARRAY_H_ + +#include "main.h" + +#include +#include +#include +#include + +/** + * batadv_test_bit() - check if bit is set in the current window + * + * @seq_bits: pointer to the sequence number bitmap of received packets + * @last_seqno: latest sequence number in seq_bits + * @curr_seqno: sequence number to test for + * + * Return: true if the corresponding bit in the given seq_bits indicates true + * and curr_seqno is within range of last_seqno. Otherwise returns false. + */ +static inline bool batadv_test_bit(const unsigned long *seq_bits, + u32 last_seqno, u32 curr_seqno) +{ + s32 diff; + + diff = last_seqno - curr_seqno; + if (diff < 0 || diff >= BATADV_TQ_LOCAL_WINDOW_SIZE) + return false; + return test_bit(diff, seq_bits) != 0; +} + +/** + * batadv_set_bit() - Turn corresponding bit on, so we can remember that we got + * the packet + * @seq_bits: bitmap of the packet receive window + * @n: relative sequence number of newly received packet + */ +static inline void batadv_set_bit(unsigned long *seq_bits, s32 n) +{ + /* if too old, just drop it */ + if (n < 0 || n >= BATADV_TQ_LOCAL_WINDOW_SIZE) + return; + + set_bit(n, seq_bits); /* turn the position on */ +} + +bool batadv_bit_get_packet(void *priv, unsigned long *seq_bits, + s32 seq_num_diff, int set_mark); + +#endif /* _NET_BATMAN_ADV_BITARRAY_H_ */ -- cgit v1.3.1