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/fault-injection/failcmd.sh | 232 +++++++++++++++++++++++++++++++ 1 file changed, 232 insertions(+) create mode 100755 tools/testing/fault-injection/failcmd.sh (limited to 'tools/testing/fault-injection/failcmd.sh') diff --git a/tools/testing/fault-injection/failcmd.sh b/tools/testing/fault-injection/failcmd.sh new file mode 100755 index 000000000..c4f243275 --- /dev/null +++ b/tools/testing/fault-injection/failcmd.sh @@ -0,0 +1,232 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 +# +# NAME +# failcmd.sh - run a command with injecting slab/page allocation failures +# +# SYNOPSIS +# failcmd.sh --help +# failcmd.sh [] command [arguments] +# +# DESCRIPTION +# Run command with injecting slab/page allocation failures by fault +# injection. +# +# NOTE: you need to run this script as root. +# + +usage() +{ + cat >&2 <&2 + exit 1 + fi +} + +if [ $UID != 0 ]; then + echo must be run as root >&2 + exit 1 +fi + +DEBUGFS=`mount -t debugfs | head -1 | awk '{ print $3}'` + +if [ ! -d "$DEBUGFS" ]; then + echo debugfs is not mounted >&2 + exit 1 +fi + +FAILCMD_TYPE=${FAILCMD_TYPE:-failslab} +FAULTATTR=$DEBUGFS/$FAILCMD_TYPE + +if [ ! -d $FAULTATTR ]; then + echo $FAILCMD_TYPE is not available >&2 + exit 1 +fi + +LONGOPTS=probability:,interval:,times:,space:,verbose:,task-filter: +LONGOPTS=$LONGOPTS,stacktrace-depth:,require-start:,require-end: +LONGOPTS=$LONGOPTS,reject-start:,reject-end:,oom-kill-allocating-task:,help + +if [ $FAILCMD_TYPE = failslab ]; then + LONGOPTS=$LONGOPTS,ignore-gfp-wait:,cache-filter: +elif [ $FAILCMD_TYPE = fail_page_alloc ]; then + LONGOPTS=$LONGOPTS,ignore-gfp-wait:,ignore-gfp-highmem:,min-order: +fi + +TEMP=`getopt -o p:i:t:s:v:h --long $LONGOPTS -n 'failcmd.sh' -- "$@"` + +if [ $? != 0 ]; then + usage + exit 1 +fi + +eval set -- "$TEMP" + +fault_attr_default() +{ + echo N > $FAULTATTR/task-filter + echo 0 > $FAULTATTR/probability + echo 1 > $FAULTATTR/times +} + +fault_attr_default + +oom_kill_allocating_task_saved=`cat /proc/sys/vm/oom_kill_allocating_task` + +restore_values() +{ + fault_attr_default + echo $oom_kill_allocating_task_saved \ + > /proc/sys/vm/oom_kill_allocating_task +} + +# +# Default options +# +declare -i oom_kill_allocating_task=1 +declare task_filter=Y +declare -i probability=1 +declare -i times=1 + +while true; do + case "$1" in + -p|--probability) + probability=$2 + shift 2 + ;; + -i|--interval) + echo $2 > $FAULTATTR/interval + shift 2 + ;; + -t|--times) + times=$2 + shift 2 + ;; + -s|--space) + echo $2 > $FAULTATTR/space + shift 2 + ;; + -v|--verbose) + echo $2 > $FAULTATTR/verbose + shift 2 + ;; + --task-filter) + task_filter=$2 + shift 2 + ;; + --stacktrace-depth) + echo $2 > $FAULTATTR/stacktrace-depth + shift 2 + ;; + --require-start) + exit_if_not_hex "$2" + echo $2 > $FAULTATTR/require-start + shift 2 + ;; + --require-end) + exit_if_not_hex "$2" + echo $2 > $FAULTATTR/require-end + shift 2 + ;; + --reject-start) + exit_if_not_hex "$2" + echo $2 > $FAULTATTR/reject-start + shift 2 + ;; + --reject-end) + exit_if_not_hex "$2" + echo $2 > $FAULTATTR/reject-end + shift 2 + ;; + --oom-kill-allocating-task) + oom_kill_allocating_task=$2 + shift 2 + ;; + --ignore-gfp-wait) + echo $2 > $FAULTATTR/ignore-gfp-wait + shift 2 + ;; + --cache-filter) + echo $2 > $FAULTATTR/cache_filter + shift 2 + ;; + --ignore-gfp-highmem) + echo $2 > $FAULTATTR/ignore-gfp-highmem + shift 2 + ;; + --min-order) + echo $2 > $FAULTATTR/min-order + shift 2 + ;; + -h|--help) + usage + exit 0 + shift + ;; + --) + shift + break + ;; + esac +done + +[ -z "$1" ] && exit 0 + +echo $oom_kill_allocating_task > /proc/sys/vm/oom_kill_allocating_task +echo $task_filter > $FAULTATTR/task-filter +echo $probability > $FAULTATTR/probability +echo $times > $FAULTATTR/times + +trap "restore_values" SIGINT SIGTERM EXIT + +cmd="echo 1 > /proc/self/make-it-fail && exec $@" +bash -c "$cmd" -- cgit v1.3.1