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/tmpfs/.gitignore | 2 + tools/testing/selftests/tmpfs/Makefile | 7 ++ tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c | 78 ++++++++++++++++++++++ 3 files changed, 87 insertions(+) create mode 100644 tools/testing/selftests/tmpfs/.gitignore create mode 100644 tools/testing/selftests/tmpfs/Makefile create mode 100644 tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c (limited to 'tools/testing/selftests/tmpfs') diff --git a/tools/testing/selftests/tmpfs/.gitignore b/tools/testing/selftests/tmpfs/.gitignore new file mode 100644 index 000000000..b1afaa925 --- /dev/null +++ b/tools/testing/selftests/tmpfs/.gitignore @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +/bug-link-o-tmpfile diff --git a/tools/testing/selftests/tmpfs/Makefile b/tools/testing/selftests/tmpfs/Makefile new file mode 100644 index 000000000..3be931e11 --- /dev/null +++ b/tools/testing/selftests/tmpfs/Makefile @@ -0,0 +1,7 @@ +# SPDX-License-Identifier: GPL-2.0-only +CFLAGS += -Wall -O2 + +TEST_GEN_PROGS := +TEST_GEN_PROGS += bug-link-o-tmpfile + +include ../lib.mk diff --git a/tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c b/tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c new file mode 100644 index 000000000..5cb4e404a --- /dev/null +++ b/tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c @@ -0,0 +1,78 @@ +/* + * Copyright (c) 2019 Alexey Dobriyan + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ +/* Test that open(O_TMPFILE), linkat() doesn't screw accounting. */ +#include +#include +#include +#include +#include +#include +#include +#include + +#include "kselftest.h" + +int main(void) +{ + int fd; + + // Setting up kselftest framework + ksft_print_header(); + ksft_set_plan(1); + + // Check if test is run as root + if (geteuid()) { + ksft_exit_skip("This test needs root to run!\n"); + return 1; + } + + if (unshare(CLONE_NEWNS) == -1) { + if (errno == ENOSYS || errno == EPERM) { + ksft_exit_skip("unshare() error: unshare, errno %d\n", errno); + } else { + ksft_exit_fail_msg("unshare() error: unshare, errno %d\n", errno); + } + } + + if (mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL) == -1) { + ksft_exit_fail_msg("mount() error: Root filesystem private mount: Fail %d\n", errno); + } + + /* Our heroes: 1 root inode, 1 O_TMPFILE inode, 1 permanent inode. */ + if (mount(NULL, "/tmp", "tmpfs", 0, "nr_inodes=3") == -1) { + ksft_exit_fail_msg("mount() error: Mounting tmpfs on /tmp: Fail %d\n", errno); + } + + fd = openat(AT_FDCWD, "/tmp", O_WRONLY|O_TMPFILE, 0600); + if (fd == -1) { + ksft_exit_fail_msg("openat() error: Open first temporary file: Fail %d\n", errno); + } + + if (linkat(fd, "", AT_FDCWD, "/tmp/1", AT_EMPTY_PATH) == -1) { + ksft_exit_fail_msg("linkat() error: Linking the temporary file: Fail %d\n", errno); + /* Ensure fd is closed on failure */ + close(fd); + } + close(fd); + + fd = openat(AT_FDCWD, "/tmp", O_WRONLY|O_TMPFILE, 0600); + if (fd == -1) { + ksft_exit_fail_msg("openat() error: Opening the second temporary file: Fail %d\n", errno); + } + ksft_test_result_pass(" "); + ksft_exit_pass(); + return 0; +} -- cgit v1.3.1