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/rlimits/.gitignore | 2 + tools/testing/selftests/rlimits/Makefile | 6 + tools/testing/selftests/rlimits/config | 1 + .../testing/selftests/rlimits/rlimits-per-userns.c | 161 +++++++++++++++++++++ 4 files changed, 170 insertions(+) create mode 100644 tools/testing/selftests/rlimits/.gitignore create mode 100644 tools/testing/selftests/rlimits/Makefile create mode 100644 tools/testing/selftests/rlimits/config create mode 100644 tools/testing/selftests/rlimits/rlimits-per-userns.c (limited to 'tools/testing/selftests/rlimits') diff --git a/tools/testing/selftests/rlimits/.gitignore b/tools/testing/selftests/rlimits/.gitignore new file mode 100644 index 000000000..091021f25 --- /dev/null +++ b/tools/testing/selftests/rlimits/.gitignore @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +rlimits-per-userns diff --git a/tools/testing/selftests/rlimits/Makefile b/tools/testing/selftests/rlimits/Makefile new file mode 100644 index 000000000..03aadb406 --- /dev/null +++ b/tools/testing/selftests/rlimits/Makefile @@ -0,0 +1,6 @@ +# SPDX-License-Identifier: GPL-2.0-or-later + +CFLAGS += -Wall -O2 -g +TEST_GEN_PROGS := rlimits-per-userns + +include ../lib.mk diff --git a/tools/testing/selftests/rlimits/config b/tools/testing/selftests/rlimits/config new file mode 100644 index 000000000..416bd53ce --- /dev/null +++ b/tools/testing/selftests/rlimits/config @@ -0,0 +1 @@ +CONFIG_USER_NS=y diff --git a/tools/testing/selftests/rlimits/rlimits-per-userns.c b/tools/testing/selftests/rlimits/rlimits-per-userns.c new file mode 100644 index 000000000..26dc949e9 --- /dev/null +++ b/tools/testing/selftests/rlimits/rlimits-per-userns.c @@ -0,0 +1,161 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Author: Alexey Gladkov + */ +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#define NR_CHILDS 2 + +static char *service_prog; +static uid_t user = 60000; +static uid_t group = 60000; + +static void setrlimit_nproc(rlim_t n) +{ + pid_t pid = getpid(); + struct rlimit limit = { + .rlim_cur = n, + .rlim_max = n + }; + + warnx("(pid=%d): Setting RLIMIT_NPROC=%ld", pid, n); + + if (setrlimit(RLIMIT_NPROC, &limit) < 0) + err(EXIT_FAILURE, "(pid=%d): setrlimit(RLIMIT_NPROC)", pid); +} + +static pid_t fork_child(void) +{ + pid_t pid = fork(); + + if (pid < 0) + err(EXIT_FAILURE, "fork"); + + if (pid > 0) + return pid; + + pid = getpid(); + + warnx("(pid=%d): New process starting ...", pid); + + if (prctl(PR_SET_PDEATHSIG, SIGKILL) < 0) + err(EXIT_FAILURE, "(pid=%d): prctl(PR_SET_PDEATHSIG)", pid); + + signal(SIGUSR1, SIG_DFL); + + warnx("(pid=%d): Changing to uid=%d, gid=%d", pid, user, group); + + if (setgid(group) < 0) + err(EXIT_FAILURE, "(pid=%d): setgid(%d)", pid, group); + if (setuid(user) < 0) + err(EXIT_FAILURE, "(pid=%d): setuid(%d)", pid, user); + + warnx("(pid=%d): Service running ...", pid); + + warnx("(pid=%d): Unshare user namespace", pid); + if (unshare(CLONE_NEWUSER) < 0) + err(EXIT_FAILURE, "unshare(CLONE_NEWUSER)"); + + char *const argv[] = { "service", NULL }; + char *const envp[] = { "I_AM_SERVICE=1", NULL }; + + warnx("(pid=%d): Executing real service ...", pid); + + execve(service_prog, argv, envp); + err(EXIT_FAILURE, "(pid=%d): execve", pid); +} + +int main(int argc, char **argv) +{ + size_t i; + pid_t child[NR_CHILDS]; + int wstatus[NR_CHILDS]; + int childs = NR_CHILDS; + pid_t pid; + + if (getenv("I_AM_SERVICE")) { + pause(); + exit(EXIT_SUCCESS); + } + + service_prog = argv[0]; + pid = getpid(); + + warnx("(pid=%d) Starting testcase", pid); + + /* + * This rlimit is not a problem for root because it can be exceeded. + */ + setrlimit_nproc(1); + + for (i = 0; i < NR_CHILDS; i++) { + child[i] = fork_child(); + wstatus[i] = 0; + usleep(250000); + } + + while (1) { + for (i = 0; i < NR_CHILDS; i++) { + if (child[i] <= 0) + continue; + + errno = 0; + pid_t ret = waitpid(child[i], &wstatus[i], WNOHANG); + + if (!ret || (!WIFEXITED(wstatus[i]) && !WIFSIGNALED(wstatus[i]))) + continue; + + if (ret < 0 && errno != ECHILD) + warn("(pid=%d): waitpid(%d)", pid, child[i]); + + child[i] *= -1; + childs -= 1; + } + + if (!childs) + break; + + usleep(250000); + + for (i = 0; i < NR_CHILDS; i++) { + if (child[i] <= 0) + continue; + kill(child[i], SIGUSR1); + } + } + + for (i = 0; i < NR_CHILDS; i++) { + if (WIFEXITED(wstatus[i])) + warnx("(pid=%d): pid %d exited, status=%d", + pid, -child[i], WEXITSTATUS(wstatus[i])); + else if (WIFSIGNALED(wstatus[i])) + warnx("(pid=%d): pid %d killed by signal %d", + pid, -child[i], WTERMSIG(wstatus[i])); + + if (WIFSIGNALED(wstatus[i]) && WTERMSIG(wstatus[i]) == SIGUSR1) + continue; + + warnx("(pid=%d): Test failed", pid); + exit(EXIT_FAILURE); + } + + warnx("(pid=%d): Test passed", pid); + exit(EXIT_SUCCESS); +} -- cgit v1.3.1