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 --- scripts/checkdeclares.pl | 53 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100755 scripts/checkdeclares.pl (limited to 'scripts/checkdeclares.pl') diff --git a/scripts/checkdeclares.pl b/scripts/checkdeclares.pl new file mode 100755 index 000000000..f6d551c84 --- /dev/null +++ b/scripts/checkdeclares.pl @@ -0,0 +1,53 @@ +#!/usr/bin/env perl +# SPDX-License-Identifier: GPL-2.0 +# +# checkdeclares: find struct declared more than once +# +# Copyright 2021 Wan Jiabing +# Inspired by checkincludes.pl +# +# This script checks for duplicate struct declares. +# Note that this will not take into consideration macros so +# you should run this only if you know you do have real dups +# and do not have them under #ifdef's. +# You could also just review the results. + +use strict; + +sub usage { + print "Usage: checkdeclares.pl file1.h ...\n"; + print "Warns of struct declaration duplicates\n"; + exit 1; +} + +if ($#ARGV < 0) { + usage(); +} + +my $dup_counter = 0; + +foreach my $file (@ARGV) { + open(my $f, '<', $file) + or die "Cannot open $file: $!.\n"; + + my %declaredstructs = (); + + while (<$f>) { + if (m/^\s*struct\s*(\w*);$/o) { + ++$declaredstructs{$1}; + } + } + + close($f); + + foreach my $structname (keys %declaredstructs) { + if ($declaredstructs{$structname} > 1) { + print "$file: struct $structname is declared more than once.\n"; + ++$dup_counter; + } + } +} + +if ($dup_counter == 0) { + print "No duplicate struct declares found.\n"; +} -- cgit v1.3.1