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 --- .../dummy-plugin-dir/include/plugin-version.h | 0 scripts/dummy-tools/gcc | 116 +++++++++++++++++++++ scripts/dummy-tools/ld | 30 ++++++ scripts/dummy-tools/nm | 1 + scripts/dummy-tools/objcopy | 1 + scripts/dummy-tools/pahole | 4 + scripts/dummy-tools/python3 | 4 + 7 files changed, 156 insertions(+) create mode 100644 scripts/dummy-tools/dummy-plugin-dir/include/plugin-version.h create mode 100755 scripts/dummy-tools/gcc create mode 100755 scripts/dummy-tools/ld create mode 120000 scripts/dummy-tools/nm create mode 120000 scripts/dummy-tools/objcopy create mode 100755 scripts/dummy-tools/pahole create mode 100755 scripts/dummy-tools/python3 (limited to 'scripts/dummy-tools') diff --git a/scripts/dummy-tools/dummy-plugin-dir/include/plugin-version.h b/scripts/dummy-tools/dummy-plugin-dir/include/plugin-version.h new file mode 100644 index 000000000..e69de29bb diff --git a/scripts/dummy-tools/gcc b/scripts/dummy-tools/gcc new file mode 100755 index 000000000..e6c41427c --- /dev/null +++ b/scripts/dummy-tools/gcc @@ -0,0 +1,116 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0-only +# +# Staring v4.18, Kconfig evaluates compiler capabilities, and hides CONFIG +# options your compiler does not support. This works well if you configure and +# build the kernel on the same host machine. +# +# It is inconvenient if you prepare the .config that is carried to a different +# build environment (typically this happens when you package the kernel for +# distros) because using a different compiler potentially produces different +# CONFIG options than the real build environment. So, you probably want to make +# as many options visible as possible. In other words, you need to create a +# super-set of CONFIG options that cover any build environment. If some of the +# CONFIG options turned out to be unsupported on the build machine, they are +# automatically disabled by the nature of Kconfig. +# +# However, it is not feasible to get a full-featured compiler for every arch. +# Hence these dummy toolchains to make all compiler tests pass. +# +# Usage: +# +# From the top directory of the source tree, run +# +# $ make CROSS_COMPILE=scripts/dummy-tools/ oldconfig +# +# Most of compiler features are tested by cc-option, which simply checks the +# exit code of $(CC). This script does nothing and just exits with 0 in most +# cases. So, $(cc-option, ...) is evaluated as 'y'. +# +# This scripts caters to more checks; handle --version and pre-process __GNUC__ +# etc. to pretend to be GCC, and also do right things to satisfy some scripts. + +# Check if the first parameter appears in the rest. Succeeds if found. +# This helper is useful if a particular option was passed to this script. +# Typically used like this: +# arg_contain "$@" +arg_contain () +{ + search="$1" + shift + + while [ $# -gt 0 ] + do + if [ "$search" = "$1" ]; then + return 0 + fi + shift + done + + return 1 +} + +# To set CONFIG_CC_IS_GCC=y +if arg_contain --version "$@"; then + echo "gcc (scripts/dummy-tools/gcc)" + exit 0 +fi + +if arg_contain -E "$@"; then + # For scripts/cc-version.sh; This emulates GCC 20.0.0 + if arg_contain - "$@"; then + sed -n '/^GCC/{s/__GNUC__/20/; s/__GNUC_MINOR__/0/; s/__GNUC_PATCHLEVEL__/0/; p;}; s/__LONG_DOUBLE_128__/1/ p' + exit 0 + else + echo "no input files" >&2 + exit 1 + fi +fi + +# To set CONFIG_AS_IS_GNU +if arg_contain -Wa,--version "$@"; then + echo "GNU assembler (scripts/dummy-tools) 2.50" + exit 0 +fi + +if arg_contain -S "$@"; then + # For scripts/gcc-x86-*-has-stack-protector.sh + if arg_contain -fstack-protector "$@"; then + if arg_contain -mstack-protector-guard-reg=fs "$@"; then + echo "%fs" + else + echo "%gs" + fi + exit 0 + fi + + # For arch/powerpc/tools/gcc-check-mprofile-kernel.sh + if arg_contain -m64 "$@" && arg_contain -mprofile-kernel "$@"; then + if ! test -t 0 && ! grep -q notrace; then + echo "_mcount" + fi + exit 0 + fi + + # For arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh + if arg_contain -m64 "$@" && arg_contain -fpatchable-function-entry=2 "$@"; then + echo "func:" + echo ".section __patchable_function_entries" + echo ".localentry" + echo " nop" + echo " nop" + exit 0 + fi +fi + +# To set GCC_PLUGINS +if arg_contain -print-file-name=plugin "$@"; then + # Use $0 to find the in-tree dummy directory + echo "$(dirname "$(readlink -f "$0")")/dummy-plugin-dir" + exit 0 +fi + +# inverted return value +if arg_contain -D__SIZEOF_INT128__=0 "$@"; then + exit 1 +fi diff --git a/scripts/dummy-tools/ld b/scripts/dummy-tools/ld new file mode 100755 index 000000000..f68233050 --- /dev/null +++ b/scripts/dummy-tools/ld @@ -0,0 +1,30 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0-only + +# Dummy script that always succeeds. + +# Check if the first parameter appears in the rest. Succeeds if found. +# This helper is useful if a particular option was passed to this script. +# Typically used like this: +# arg_contain "$@" +arg_contain () +{ + search="$1" + shift + + while [ $# -gt 0 ] + do + if [ "$search" = "$1" ]; then + return 0 + fi + shift + done + + return 1 +} + +if arg_contain --version "$@" || arg_contain -v "$@"; then + progname=$(basename $0) + echo "GNU $progname (scripts/dummy-tools/$progname) 2.50" + exit 0 +fi diff --git a/scripts/dummy-tools/nm b/scripts/dummy-tools/nm new file mode 120000 index 000000000..c0648b38d --- /dev/null +++ b/scripts/dummy-tools/nm @@ -0,0 +1 @@ +ld \ No newline at end of file diff --git a/scripts/dummy-tools/objcopy b/scripts/dummy-tools/objcopy new file mode 120000 index 000000000..c0648b38d --- /dev/null +++ b/scripts/dummy-tools/objcopy @@ -0,0 +1 @@ +ld \ No newline at end of file diff --git a/scripts/dummy-tools/pahole b/scripts/dummy-tools/pahole new file mode 100755 index 000000000..53501a36f --- /dev/null +++ b/scripts/dummy-tools/pahole @@ -0,0 +1,4 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0-only + +echo v99.99 diff --git a/scripts/dummy-tools/python3 b/scripts/dummy-tools/python3 new file mode 100755 index 000000000..24c558486 --- /dev/null +++ b/scripts/dummy-tools/python3 @@ -0,0 +1,4 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0-only + +true -- cgit v1.3.1