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/fchmodat2/.gitignore | 2 + tools/testing/selftests/fchmodat2/Makefile | 15 ++ tools/testing/selftests/fchmodat2/fchmodat2_test.c | 200 +++++++++++++++++++++ 3 files changed, 217 insertions(+) create mode 100644 tools/testing/selftests/fchmodat2/.gitignore create mode 100644 tools/testing/selftests/fchmodat2/Makefile create mode 100644 tools/testing/selftests/fchmodat2/fchmodat2_test.c (limited to 'tools/testing/selftests/fchmodat2') diff --git a/tools/testing/selftests/fchmodat2/.gitignore b/tools/testing/selftests/fchmodat2/.gitignore new file mode 100644 index 000000000..82a4846cb --- /dev/null +++ b/tools/testing/selftests/fchmodat2/.gitignore @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +/*_test diff --git a/tools/testing/selftests/fchmodat2/Makefile b/tools/testing/selftests/fchmodat2/Makefile new file mode 100644 index 000000000..4373cea79 --- /dev/null +++ b/tools/testing/selftests/fchmodat2/Makefile @@ -0,0 +1,15 @@ +# SPDX-License-Identifier: GPL-2.0-or-later + +CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined $(KHDR_INCLUDES) + +# gcc requires -static-libasan in order to ensure that Address Sanitizer's +# library is the first one loaded. However, clang already statically links the +# Address Sanitizer if -fsanitize is specified. Therefore, simply omit +# -static-libasan for clang builds. +ifeq ($(LLVM),) + CFLAGS += -static-libasan +endif + +TEST_GEN_PROGS := fchmodat2_test + +include ../lib.mk diff --git a/tools/testing/selftests/fchmodat2/fchmodat2_test.c b/tools/testing/selftests/fchmodat2/fchmodat2_test.c new file mode 100644 index 000000000..8e1b6384b --- /dev/null +++ b/tools/testing/selftests/fchmodat2/fchmodat2_test.c @@ -0,0 +1,200 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#define _GNU_SOURCE +#include +#include +#include +#include +#include + +#include "kselftest.h" + +struct testdir { + char *dirname; + int dfd; +}; + +int sys_fchmodat2(int dfd, const char *filename, mode_t mode, int flags) +{ + int ret = syscall(__NR_fchmodat2, dfd, filename, mode, flags); + + return ret >= 0 ? ret : -errno; +} + +static void setup_testdir(struct testdir *testdir) +{ + int ret, dfd; + char dirname[] = "/tmp/ksft-fchmodat2.XXXXXX"; + + /* Make the top-level directory. */ + if (!mkdtemp(dirname)) + ksft_exit_fail_msg("%s: failed to create tmpdir\n", __func__); + + dfd = open(dirname, O_PATH | O_DIRECTORY); + if (dfd < 0) { + ksft_perror("failed to open tmpdir"); + goto err; + } + + ret = openat(dfd, "regfile", O_CREAT | O_WRONLY | O_TRUNC, 0644); + if (ret < 0) { + ksft_perror("failed to create file in tmpdir"); + goto err; + } + close(ret); + + ret = symlinkat("regfile", dfd, "symlink"); + if (ret < 0) { + ksft_perror("symlinkat() failed"); + goto err_regfile; + } + + testdir->dirname = strdup(dirname); + if (!testdir->dirname) { + ksft_perror("Out of memory"); + goto err_symlink; + } + testdir->dfd = dfd; + + return; + +err_symlink: + unlinkat(testdir->dfd, "symlink", 0); +err_regfile: + unlinkat(testdir->dfd, "regfile", 0); +err: + unlink(dirname); + ksft_exit_fail(); +} + +static void cleanup_testdir(struct testdir *testdir) +{ + unlinkat(testdir->dfd, "regfile", 0); + unlinkat(testdir->dfd, "symlink", 0); + rmdir(testdir->dirname); + free(testdir->dirname); +} + +int expect_mode(int dfd, const char *filename, mode_t expect_mode) +{ + struct stat st; + int ret = fstatat(dfd, filename, &st, AT_SYMLINK_NOFOLLOW); + + if (ret) { + ksft_perror("fstatat() failed\n"); + return 0; + } + + return (st.st_mode == expect_mode); +} + +void test_regfile(void) +{ + struct testdir testdir; + int ret; + + setup_testdir(&testdir); + + ret = sys_fchmodat2(testdir.dfd, "regfile", 0640, 0); + + if (ret < 0) { + ksft_perror("fchmodat2(noflag) failed"); + goto out; + } + + if (!expect_mode(testdir.dfd, "regfile", 0100640)) { + ksft_print_msg("%s: wrong file mode bits after fchmodat2\n", + __func__); + ret = 1; + goto out; + } + + ret = sys_fchmodat2(testdir.dfd, "regfile", 0600, AT_SYMLINK_NOFOLLOW); + + if (ret < 0) { + ksft_perror("fchmodat2(AT_SYMLINK_NOFOLLOW) failed"); + goto out; + } + + if (!expect_mode(testdir.dfd, "regfile", 0100600)) { + ksft_print_msg("%s: wrong file mode bits after fchmodat2 with nofollow\n", + __func__); + ret = 1; + } + +out: + ksft_test_result(ret == 0, "fchmodat2(regfile)\n"); + cleanup_testdir(&testdir); +} + +void test_symlink(void) +{ + struct testdir testdir; + int ret; + + setup_testdir(&testdir); + + ret = sys_fchmodat2(testdir.dfd, "symlink", 0640, 0); + + if (ret < 0) { + ksft_perror("fchmodat2(noflag) failed"); + goto err; + } + + if (!expect_mode(testdir.dfd, "regfile", 0100640)) { + ksft_print_msg("%s: wrong file mode bits after fchmodat2\n", + __func__); + goto err; + } + + if (!expect_mode(testdir.dfd, "symlink", 0120777)) { + ksft_print_msg("%s: wrong symlink mode bits after fchmodat2\n", + __func__); + goto err; + } + + ret = sys_fchmodat2(testdir.dfd, "symlink", 0600, AT_SYMLINK_NOFOLLOW); + + /* + * On certain filesystems (xfs or btrfs), chmod operation fails. So we + * first check the symlink target but if the operation fails we mark the + * test as skipped. + * + * https://sourceware.org/legacy-ml/libc-alpha/2020-02/msg00467.html + */ + if (ret == 0 && !expect_mode(testdir.dfd, "symlink", 0120600)) { + ksft_print_msg("%s: wrong symlink mode bits after fchmodat2 with nofollow\n", + __func__); + ret = 1; + goto err; + } + + if (!expect_mode(testdir.dfd, "regfile", 0100640)) { + ksft_print_msg("%s: wrong file mode bits after fchmodat2 with nofollow\n", + __func__); + } + + if (ret != 0) + ksft_test_result_skip("fchmodat2(symlink)\n"); + else + ksft_test_result_pass("fchmodat2(symlink)\n"); + cleanup_testdir(&testdir); + return; + +err: + ksft_test_result_fail("fchmodat2(symlink)\n"); + cleanup_testdir(&testdir); +} + +#define NUM_TESTS 2 + +int main(int argc, char **argv) +{ + ksft_print_header(); + ksft_set_plan(NUM_TESTS); + + test_regfile(); + test_symlink(); + + ksft_finished(); +} -- cgit v1.3.1