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 --- tools/testing/selftests/rust/Makefile | 4 +++ tools/testing/selftests/rust/config | 6 ++++ tools/testing/selftests/rust/test_probe_samples.sh | 41 ++++++++++++++++++++++ 3 files changed, 51 insertions(+) create mode 100644 tools/testing/selftests/rust/Makefile create mode 100644 tools/testing/selftests/rust/config create mode 100755 tools/testing/selftests/rust/test_probe_samples.sh (limited to 'tools/testing/selftests/rust') diff --git a/tools/testing/selftests/rust/Makefile b/tools/testing/selftests/rust/Makefile new file mode 100644 index 000000000..fce1584d3 --- /dev/null +++ b/tools/testing/selftests/rust/Makefile @@ -0,0 +1,4 @@ +# SPDX-License-Identifier: GPL-2.0 +TEST_PROGS += test_probe_samples.sh + +include ../lib.mk diff --git a/tools/testing/selftests/rust/config b/tools/testing/selftests/rust/config new file mode 100644 index 000000000..5f942b5c8 --- /dev/null +++ b/tools/testing/selftests/rust/config @@ -0,0 +1,6 @@ +# CONFIG_GCC_PLUGINS is not set +CONFIG_RUST=y +CONFIG_SAMPLES=y +CONFIG_SAMPLES_RUST=y +CONFIG_SAMPLE_RUST_MINIMAL=m +CONFIG_SAMPLE_RUST_PRINT=m diff --git a/tools/testing/selftests/rust/test_probe_samples.sh b/tools/testing/selftests/rust/test_probe_samples.sh new file mode 100755 index 000000000..ad0397e49 --- /dev/null +++ b/tools/testing/selftests/rust/test_probe_samples.sh @@ -0,0 +1,41 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 +# +# Copyright (c) 2023 Collabora Ltd +# +# This script tests whether the rust sample modules can +# be added and removed correctly. +# +DIR="$(dirname "$(readlink -f "$0")")" + +KTAP_HELPERS="${DIR}/../kselftest/ktap_helpers.sh" +if [ -e "$KTAP_HELPERS" ]; then + source "$KTAP_HELPERS" +else + echo "$KTAP_HELPERS file not found [SKIP]" + exit 4 +fi + +rust_sample_modules=("rust_minimal" "rust_print") + +ktap_print_header + +for sample in "${rust_sample_modules[@]}"; do + if ! /sbin/modprobe -n -q "$sample"; then + ktap_skip_all "module $sample is not found in /lib/modules/$(uname -r)" + exit "$KSFT_SKIP" + fi +done + +ktap_set_plan "${#rust_sample_modules[@]}" + +for sample in "${rust_sample_modules[@]}"; do + if /sbin/modprobe -q "$sample"; then + /sbin/modprobe -q -r "$sample" + ktap_test_pass "$sample" + else + ktap_test_fail "$sample" + fi +done + +ktap_finished -- cgit v1.3.1