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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Matthew Wilcox , Bas van Dijk , Eero Kelly , Andrew Battat , Adam Bratschi-Kaye , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v4] selftests/mm: add folio_split() and filemap_get_entry() race test Date: Fri, 20 Mar 2026 10:22:19 -0400 Message-ID: <20260320142219.375118-1-ziy@nvidia.com> X-Mailer: git-send-email 2.51.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: YQZPR01CA0154.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:8c::13) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|DM4PR12MB6376:EE_ X-MS-Office365-Filtering-Correlation-Id: 6eff8e2a-1d31-4839-a982-08de868c1f71 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|7416014|376014|18002099003|56012099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?JZyB/hIp0OrbG3pQFFhzyuUPFJ7DiE3k/M+3P43BQxaMyG4XrNbjBujEk+Kv?= =?us-ascii?Q?UaV8mu80J+pUU7ms2JZpu1ldSwFtfNM6LXFfD881HKKWdNn/FquGpVBksiQu?= =?us-ascii?Q?ijALLDqbKcBA+xpiL0EPBylyH7GofEyjIQSrE2sHIU9vK+LLGjWx8npOwC7L?= =?us-ascii?Q?ntasDVHFuWp1rpk71mAsJOzlqUth9tflnm7tg8YI2Kg1XrIkcggyKpvxnSdT?= =?us-ascii?Q?lMx1o5IULWxRwj002ek52W+BQf7DTr0zmcKPDsW+ZmO78utI1eThDAtU+1Xd?= =?us-ascii?Q?F33oWuiHKn8L1ku8L3fJItqcvE2PcdNPk2Z1e36g1cBVOKZMhWEv4K87zCLY?= =?us-ascii?Q?u3zn15ahydEBHyIRwwLjFZeGx4nW2pfQjNphyYaOYz85bfEw7cohZukNI7we?= =?us-ascii?Q?SDQADcagQZH8Fhnlcw+oA53MnQ4I8JLeUojsX39IsZDcq88ByaNFTDwYv8hG?= =?us-ascii?Q?zbNsSrF+zHfPL6ikdD4wnk0AxJ0iGFBJ8MWX9BmuyCpdhtsX0vlQDnbM1Dtr?= =?us-ascii?Q?KNRZs63ApVI/50FcTOxvD/Eczqou6g/xeOHGPZVWbU+TpwMbyh7xgu5xdtdo?= =?us-ascii?Q?0iAICDwJsjn/ujWZmEIdfmoM76VKOmUDFeAtRqTrJYCE64hXy0TYzZirzDxh?= =?us-ascii?Q?2o4HhPO1LaOXb/FnV/iRHs3jbKuKUVrslfxieyWEs2JWfEaLigXrZh6fAf6t?= =?us-ascii?Q?V4Ztem6e5GmgelNg0uMBU5f+o+fRMIbqREYmeIQrx//uW2jPYEOi4DkrVNP6?= =?us-ascii?Q?cRxZCcT6kxJVh4gkKF70YgE3eLwQbFhbR+L3bjiDc1x/GaZzNViGcsSNV9bG?= =?us-ascii?Q?dthyvMu+WggZq0Wk0wP8FVny+Mi/RHMpTq62EHpW2S4VGSLlUzqAwde1sNJ/?= =?us-ascii?Q?yGL1KaPME1StnKszDyf7xSI7XMY+y4+Nc6rmI02RJW/58eieALo7ngtuy+HF?= =?us-ascii?Q?YsgGaiUeswjP0TgzcTHZF08j4jrMRGN6Oqov2JOF1UW3uiyY37LDy2T0iKyU?= =?us-ascii?Q?k/f8T5Z/C50b/FJNJ8w+cqJtnJ9Bg/LPlwKZOvJiwqsXjfm5YAKQyH2I9Ksi?= =?us-ascii?Q?UZkWZPwdhwsv8e88Gj8kaO305Ob4WCerj4p7Pr6d5B+LtLt/LMXSx7hwjzjU?= =?us-ascii?Q?9Uj2Vn1ZMwKfXaFuXcigL8TWDCqDnchr667oPfanLTN+0WMjL1tAcukgTf7Z?= =?us-ascii?Q?68mwidlbvOxPBBUF2VSyZMlxHGWfubWTAwp8fHdkjTV9yoP7MCKaZAv7k0+Q?= =?us-ascii?Q?n1yB2q4IeD74azoJXc4bRR2+JalYBK2PG/1wqdE45flAcfIEIAFU+rtZOELd?= =?us-ascii?Q?cFjr8F6GYIlGoGqT30A/JX2YyNmsOeU182ECPj3x6xHyYoWQuJrS6JcyzINp?= =?us-ascii?Q?x3wV/O4xOx5JBh/fBzX6jzByw3bQkjxD8j154lVzx0jIiuuOG4KVo8oBLlQx?= =?us-ascii?Q?fr8IY98e/lySysM12vhCtV0tjDtPreDpF5ORJC/nWo9FzMT0Z2cmvBoVxUDn?= =?us-ascii?Q?qplndEvGDnDTm51AXTnY/yxhxwTNYfSfvzYfvNy2duvIiEPCHU7Ycw+RDqu0?= =?us-ascii?Q?aqihgDtZbnVtnpC8ohLlclMV4p5MATf5CU4TwUO7ANlgNAuHaE9qToQDQ/4G?= =?us-ascii?Q?PuTicaR+Cl5quscnAC5eoNonB9Zv9oe+ucoYDJj22RTlsWi0QzO3ybhefkhd?= =?us-ascii?Q?Rxjs6Pgj+Arbo/A3lm133Xz0biwwOJYoien/22u9YJN6FSWPuTqrPz4xTHI0?= =?us-ascii?Q?RiV8qW6ZDw=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6eff8e2a-1d31-4839-a982-08de868c1f71 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Mar 2026 14:22:31.6492 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 5igPMcN7IvDbJ/zaRLnu3pE4xrrSJ3JrEwVP77JDA+2zYifX5nT4FcXoxureyzK9 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6376 The added folio_split_race_test is a modified C port of the race condition test from [1]. The test creates shmem huge pages, where the main thread punches holes in the shmem to cause folio_split() in the kernel and a set of 16 threads reads the shmem to cause filemap_get_entry() in the kernel. filemap_get_entry() reads the folio and xarray split by folio_split() locklessly. The original test[2] is written in rust and uses memfd (shmem backed). This C port uses shmem directly and use a single process. Note: the initial rust to C conversion is done by Cursor. Link: https://lore.kernel.org/all/CAKNNEtw5_kZomhkugedKMPOG-sxs5Q5OLumWJdiWXv+C9Yct0w@mail.gmail.com/ [1] Link: https://github.com/dfinity/thp-madv-remove-test [2] Signed-off-by: Bas van Dijk Signed-off-by: Adam Bratschi-Kaye Signed-off-by: Zi Yan --- >From V3: 1. fixed for loop stepping issue 2. used PRIu64 instead of %zu for uint64_t. >From V2: 1. simplied the program by removing fork. >From V1: 1. added prctl(PR_SET_PDEATHSIG, SIGTERM) to avoid child looping forever. 2. removed page_idx % PUNCH_INTERVAL >= 0, since it is a nop. Added a comment. 3. added a child process status check to prevent parent looping forever and record that as a failure. 4. used ksft_exit_skip() instead of ksft_finished() when the program is not running as root. 5. restored THP settings properly when the program exits abnormally. tools/testing/selftests/mm/Makefile | 1 + .../selftests/mm/folio_split_race_test.c | 293 ++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 2 + 3 files changed, 296 insertions(+) create mode 100644 tools/testing/selftests/mm/folio_split_race_test.c diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index 7a5de4e9bf520..cd24596cdd27e 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -105,6 +105,7 @@ TEST_GEN_FILES += droppable TEST_GEN_FILES += guard-regions TEST_GEN_FILES += merge TEST_GEN_FILES += rmap +TEST_GEN_FILES += folio_split_race_test ifneq ($(ARCH),arm64) TEST_GEN_FILES += soft-dirty diff --git a/tools/testing/selftests/mm/folio_split_race_test.c b/tools/testing/selftests/mm/folio_split_race_test.c new file mode 100644 index 0000000000000..c264cc625a7cb --- /dev/null +++ b/tools/testing/selftests/mm/folio_split_race_test.c @@ -0,0 +1,293 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * The test creates shmem PMD huge pages, fills all pages with known patterns, + * then continuously verifies non-punched pages with 16 threads. Meanwhile, the + * main thread punches holes via MADV_REMOVE on the shmem. + * + * It tests the race condition between folio_split() and filemap_get_entry(), + * where the hole punches on shmem lead to folio_split() and reading the shmem + * lead to filemap_get_entry(). + */ + +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include "vm_util.h" +#include "kselftest.h" +#include "thp_settings.h" + +uint64_t page_size; +uint64_t pmd_pagesize; +#define NR_PMD_PAGE 5 +#define FILE_SIZE (pmd_pagesize * NR_PMD_PAGE) +#define TOTAL_PAGES (FILE_SIZE / page_size) + +/* Every N-th to N+M-th pages are punched; not aligned with huge page boundaries. */ +#define PUNCH_INTERVAL 50 /* N */ +#define PUNCH_SIZE_FACTOR 3 /* M */ + +#define NUM_READER_THREADS 16 +#define FILL_BYTE 0xAF +#define NUM_ITERATIONS 100 + +/* Shared control block: control reading threads and record stats */ +struct shared_ctl { + atomic_uint_fast32_t stop; + atomic_size_t reader_failures; + atomic_size_t reader_verified; +}; + +static void fill_page(unsigned char *base, size_t page_idx) +{ + unsigned char *page_ptr = base + page_idx * page_size; + uint64_t idx = (uint64_t)page_idx; + + memset(page_ptr, FILL_BYTE, page_size); + memcpy(page_ptr, &idx, sizeof(idx)); +} + +/* Returns true if valid, false if corrupted. */ +static bool check_page(unsigned char *base, size_t page_idx) +{ + unsigned char *page_ptr = base + page_idx * page_size; + uint64_t expected_idx = (uint64_t)page_idx; + uint64_t got_idx; + + memcpy(&got_idx, page_ptr, 8); + + if (got_idx != expected_idx) { + size_t off; + int all_zero = 1; + + for (off = 0; off < page_size; off++) { + if (page_ptr[off] != 0) { + all_zero = 0; + break; + } + } + if (all_zero) { + ksft_print_msg( + "CORRUPTED: page %zu (huge page %zu) is ALL ZEROS\n", + page_idx, + (page_idx * page_size) / pmd_pagesize); + } else { + ksft_print_msg( + "CORRUPTED: page %zu (huge page %zu): expected idx %zu, got %lu\n", + page_idx, (page_idx * page_size) / pmd_pagesize, + page_idx, (unsigned long)got_idx); + } + return false; + } + return true; +} + +struct reader_arg { + unsigned char *base; + struct shared_ctl *ctl; + int tid; + atomic_size_t *failures; + atomic_size_t *verified; +}; + +static void *reader_thread(void *arg) +{ + struct reader_arg *ra = (struct reader_arg *)arg; + unsigned char *base = ra->base; + struct shared_ctl *ctl = ra->ctl; + int tid = ra->tid; + atomic_size_t *failures = ra->failures; + atomic_size_t *verified = ra->verified; + size_t page_idx; + + while (atomic_load_explicit(&ctl->stop, memory_order_acquire) == 0) { + for (page_idx = (size_t)tid; page_idx < TOTAL_PAGES; + page_idx += NUM_READER_THREADS) { + /* + * page_idx % PUNCH_INTERVAL is in [0, PUNCH_INTERVAL), + * skip [0, PUNCH_SIZE_FACTOR) + */ + if (page_idx % PUNCH_INTERVAL < PUNCH_SIZE_FACTOR) + continue; + if (check_page(base, page_idx)) + atomic_fetch_add_explicit(verified, 1, + memory_order_relaxed); + else + atomic_fetch_add_explicit(failures, 1, + memory_order_relaxed); + } + if (atomic_load_explicit(failures, memory_order_relaxed) > 0) + break; + } + + return NULL; +} + +static void create_readers(pthread_t *threads, struct reader_arg *args, + unsigned char *base, struct shared_ctl *ctl) +{ + int i; + + for (i = 0; i < NUM_READER_THREADS; i++) { + args[i].base = base; + args[i].ctl = ctl; + args[i].tid = i; + args[i].failures = &ctl->reader_failures; + args[i].verified = &ctl->reader_verified; + if (pthread_create(&threads[i], NULL, reader_thread, + &args[i]) != 0) + ksft_exit_fail_msg("pthread_create failed\n"); + } +} + +/* Run a single iteration. Returns total number of corrupted pages. */ +static size_t run_iteration(void) +{ + size_t reader_failures, reader_verified; + struct reader_arg args[NUM_READER_THREADS]; + pthread_t threads[NUM_READER_THREADS]; + unsigned char *mmap_base; + struct shared_ctl ctl; + size_t i; + + memset(&ctl, 0, sizeof(struct shared_ctl)); + + mmap_base = mmap(NULL, FILE_SIZE, PROT_READ | PROT_WRITE, + MAP_SHARED | MAP_ANONYMOUS, -1, 0); + + if (mmap_base == MAP_FAILED) + ksft_exit_fail_msg("mmap failed: %d\n", errno); + + if (madvise(mmap_base, FILE_SIZE, MADV_HUGEPAGE) != 0) + ksft_exit_fail_msg("madvise(MADV_HUGEPAGE) failed: %d\n", + errno); + + for (i = 0; i < TOTAL_PAGES; i++) + fill_page(mmap_base, i); + + if (!check_huge_shmem(mmap_base, NR_PMD_PAGE, pmd_pagesize)) + ksft_exit_fail_msg("No shmem THP is allocated\n"); + + create_readers(threads, args, mmap_base, &ctl); + + for (i = 0; i < TOTAL_PAGES; i++) { + if (i % PUNCH_INTERVAL != 0) + continue; + if (madvise(mmap_base + i * page_size, + PUNCH_SIZE_FACTOR * page_size, MADV_REMOVE) != 0) { + ksft_exit_fail_msg( + "madvise(MADV_REMOVE) failed on page %zu: %d\n", + i, errno); + } + + i += PUNCH_SIZE_FACTOR - 1; + } + + atomic_store_explicit(&ctl.stop, 1, memory_order_release); + + for (i = 0; i < NUM_READER_THREADS; i++) + pthread_join(threads[i], NULL); + + reader_failures = atomic_load_explicit(&ctl.reader_failures, + memory_order_acquire); + reader_verified = atomic_load_explicit(&ctl.reader_verified, + memory_order_acquire); + if (reader_failures) + ksft_print_msg("Child: %zu pages verified, %zu failures\n", + reader_verified, reader_failures); + + munmap(mmap_base, FILE_SIZE); + + return reader_failures; +} + +static void thp_cleanup_handler(int signum) +{ + thp_restore_settings(); + /* + * Restore default handler and re-raise the signal to exit. + * This is to ensure the test process exits with the correct + * status code corresponding to the signal. + */ + signal(signum, SIG_DFL); + raise(signum); +} + +static void thp_settings_cleanup(void) +{ + thp_restore_settings(); +} + +int main(void) +{ + struct thp_settings current_settings; + bool failed = false; + size_t failures; + size_t iter; + + ksft_print_header(); + + if (!thp_is_enabled()) + ksft_exit_skip("Transparent Hugepages not available\n"); + + if (geteuid() != 0) + ksft_exit_skip("Please run the test as root\n"); + + thp_save_settings(); + /* make sure thp settings are restored */ + if (atexit(thp_settings_cleanup) != 0) + ksft_exit_fail_msg("atexit failed\n"); + + signal(SIGINT, thp_cleanup_handler); + signal(SIGTERM, thp_cleanup_handler); + + thp_read_settings(¤t_settings); + current_settings.shmem_enabled = SHMEM_ADVISE; + thp_write_settings(¤t_settings); + + ksft_set_plan(1); + + page_size = getpagesize(); + pmd_pagesize = read_pmd_pagesize(); + + ksft_print_msg("folio split race test\n"); + ksft_print_msg("===================================================\n"); + ksft_print_msg("Shmem size: %" PRIu64 " MiB\n", FILE_SIZE / 1024 / 1024); + ksft_print_msg("Total pages: %" PRIu64 "\n", TOTAL_PAGES); + ksft_print_msg("Child readers: %d\n", NUM_READER_THREADS); + ksft_print_msg("Punching every %dth to %dth page\n", PUNCH_INTERVAL, + PUNCH_INTERVAL + PUNCH_SIZE_FACTOR); + ksft_print_msg("Iterations: %d\n", NUM_ITERATIONS); + + for (iter = 1; iter <= NUM_ITERATIONS; iter++) { + failures = run_iteration(); + if (failures > 0) { + failed = true; + ksft_print_msg( + "FAILED on iteration %zu: %zu pages corrupted by MADV_REMOVE!\n", + iter, failures); + break; + } + } + + if (failed) { + ksft_test_result_fail("Test failed\n"); + ksft_exit_fail(); + } else { + ksft_test_result_pass("All %d iterations passed\n", + NUM_ITERATIONS); + ksft_exit_pass(); + } + + return 0; +} diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh index 606558cc3b098..530980fdf3227 100755 --- a/tools/testing/selftests/mm/run_vmtests.sh +++ b/tools/testing/selftests/mm/run_vmtests.sh @@ -553,6 +553,8 @@ if [ -n "${MOUNTED_XFS}" ]; then rm -f ${XFS_IMG} fi +CATEGORY="thp" run_test ./folio_split_race_test + CATEGORY="migration" run_test ./migration CATEGORY="mkdirty" run_test ./mkdirty -- 2.51.0