Fork a process that maps a device DAX instance with a PUD, in a VMA whose page tables fork copies because it has a guard region. The child must account the copied PUD in its RssFile.
Without a reference, an rmap and a counter for the copied PUD, the child's RssFile misses the PUD, and its exit leaves the child's file counter negative: "Bad rss-counter state". It runs only on a device named in argv[1] or $FORK_DAX_PUD_DEVICE: on a kernel without the fix it leaves the device folio's mapcount below zero. Assisted-by: LLM Signed-off-by: Konstantin Khorenko <[email protected]> --- MAINTAINERS | 1 + tools/testing/selftests/mm/Makefile | 1 + tools/testing/selftests/mm/fork_dax_pud.c | 136 ++++++++++++++++++++++++++++++ tools/testing/selftests/mm/run_vmtests.sh | 1 + 4 files changed, 139 insertions(+) diff --git a/MAINTAINERS b/MAINTAINERS index 7b5cab72d851b..48653704007f3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17481,6 +17481,7 @@ F: include/trace/events/huge_memory.h F: mm/huge_memory.c F: mm/khugepaged.c F: mm/mm_slot.h +F: tools/testing/selftests/mm/fork_dax_pud.c F: tools/testing/selftests/mm/khugepaged.c F: tools/testing/selftests/mm/split_huge_page_test.c F: tools/testing/selftests/mm/transhuge-stress.c diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index 2d5366196e309..86914aaf8e6ad 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -104,6 +104,7 @@ TEST_GEN_FILES += guard-regions TEST_GEN_FILES += merge TEST_GEN_FILES += rmap TEST_GEN_FILES += folio_split_race_test +TEST_GEN_FILES += fork_dax_pud ifneq ($(ARCH),arm64) TEST_GEN_FILES += soft-dirty diff --git a/tools/testing/selftests/mm/fork_dax_pud.c b/tools/testing/selftests/mm/fork_dax_pud.c new file mode 100644 index 0000000000000..1fcf46341ace2 --- /dev/null +++ b/tools/testing/selftests/mm/fork_dax_pud.c @@ -0,0 +1,136 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * fork() of a process that maps a device DAX instance with a PUD, in a VMA + * whose page tables fork copies because it has a guard region. The child + * must account the copied PUD in its RssFile. + * + * Runs only on a device named in argv[1] or $FORK_DAX_PUD_DEVICE that + * nothing else maps, with 1 GiB alignment and at least 2 GiB. To make one + * on pmem emulated in RAM, with CONFIG_X86_PMEM_LEGACY and + * CONFIG_DEV_DAX_PMEM: + * + * boot with memmap=3G!4G + * ndctl create-namespace -f -e namespace0.0 -m devdax -a 1G + * FORK_DAX_PUD_DEVICE=/dev/dax0.0 ./fork_dax_pud + */ +#define _GNU_SOURCE +#include <asm-generic/mman.h> /* Force the import of the tools version. */ +#include <errno.h> +#include <fcntl.h> +#include <limits.h> +#include <setjmp.h> +#include <signal.h> +#include <stdbool.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#include <sys/mman.h> +#include <sys/wait.h> + +#include "kselftest.h" +#include "vm_util.h" + +#define SZ_1G (1UL << 30) +#define DAX_SYSFS "/sys/bus/dax/devices" + +static sigjmp_buf sigbus_jmp; + +static void sigbus_handler(int sig) +{ + siglongjmp(sigbus_jmp, 1); +} + +static unsigned long sysfs_ul(const char *dev, const char *attr) +{ + char path[PATH_MAX], buf[64]; + unsigned long val = 0; + FILE *f; + + snprintf(path, sizeof(path), DAX_SYSFS "/%s/%s", dev, attr); + f = fopen(path, "r"); + if (!f) + return 0; + if (fgets(buf, sizeof(buf), f)) + val = strtoul(buf, NULL, 0); + fclose(f); + return val; +} + +static bool dax_dev_ok(const char *path) +{ + const char *name = strrchr(path, '/'); + + name = name ? name + 1 : path; + return sysfs_ul(name, "align") == SZ_1G && + sysfs_ul(name, "size") >= 2 * SZ_1G; +} + +static long rss_file_kb(void) +{ + char line[256]; + long kb = -1; + FILE *f = fopen("/proc/self/status", "r"); + + if (!f) + return -1; + while (fgets(line, sizeof(line), f)) + if (sscanf(line, "RssFile: %ld", &kb) == 1) + break; + fclose(f); + return kb; +} + +int main(int argc, char **argv) +{ + const char *path = argc > 1 ? argv[1] : getenv("FORK_DAX_PUD_DEVICE"); + char *area, *mem; + int fd, status; + pid_t pid; + + ksft_print_header(); + if (!path) + ksft_exit_skip("no devdax device given\n"); + if (!dax_dev_ok(path)) + ksft_exit_skip("%s: needs 1 GiB alignment and 2 GiB\n", path); + + fd = open(path, O_RDONLY); + if (fd < 0) + ksft_exit_skip("%s: %s\n", path, strerror(errno)); + area = mmap(NULL, 3 * SZ_1G, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (area == MAP_FAILED) + ksft_exit_fail_perror("mmap"); + mem = (char *)(((unsigned long)area + SZ_1G - 1) & ~(SZ_1G - 1)); + mem = mmap(mem, 2 * SZ_1G, PROT_READ, MAP_SHARED | MAP_FIXED, fd, 0); + if (mem == MAP_FAILED) + ksft_exit_skip("mmap %s: %s\n", path, strerror(errno)); + + /* A PUD in the first GiB, a guard page at the end of the second. */ + signal(SIGBUS, sigbus_handler); + if (sigsetjmp(sigbus_jmp, 1)) + ksft_exit_skip("%s cannot be mapped with a PUD\n", path); + FORCE_READ(mem[0]); + signal(SIGBUS, SIG_DFL); + if (madvise(mem + 2 * SZ_1G - getpagesize(), getpagesize(), + MADV_GUARD_INSTALL)) + ksft_exit_skip("MADV_GUARD_INSTALL: %s\n", strerror(errno)); + + ksft_set_plan(1); + fflush(stdout); + pid = fork(); + if (pid < 0) + ksft_exit_fail_perror("fork"); + if (!pid) + _exit(rss_file_kb() < (long)(SZ_1G >> 10) ? 10 : 0); + if (waitpid(pid, &status, 0) != pid) + ksft_exit_fail_perror("waitpid"); + + if (!WIFEXITED(status) || WEXITSTATUS(status)) + ksft_test_result_fail("child does not account the copied PUD\n"); + else + ksft_test_result_pass("devdax PUD copied by fork\n"); + + munmap(area, 3 * SZ_1G); + close(fd); + ksft_finished(); +} diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh index d09f9f6a384ee..7294e1334d1da 100755 --- a/tools/testing/selftests/mm/run_vmtests.sh +++ b/tools/testing/selftests/mm/run_vmtests.sh @@ -445,6 +445,7 @@ fi CATEGORY="thp" run_test ./transhuge-stress -d 20 CATEGORY="thp" run_test ./folio_split_race_test +CATEGORY="thp" run_test ./fork_dax_pud CATEGORY="migration" run_test ./migration -- 2.43.0
