[LTP] [PATCH v2] mtest06/mmap1: rewrite to newlib

Cyril Hrubis
2018-11-29T13:44:12Z

Hi!
> Instead each mmap/munmap increases a map/unmap counter. Upon hitting
> SIGSEGV or when comparing read value, these counter values are used
> to determine state of mapped area as observed by first thread.
> This isn't 100% accurrate as first thread might be faster than the
> check, but it allows second thread to race against map/unmap for
> its entire duration.

Looks good to me, using atomic counters and comparing values before and
after we access the memory is very clever as well. You can add my
Reviewed-by.

Very minor comments below.

> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2018 Jan Stancek. All rights reserved.
> + */
> +/*
> + * Test: Spawn 2 threads. First thread maps, writes and unmaps
> + * an area. Second thread tries to read from it. Second thread
> + * races against first thread. There is no synchronization
> + * between threads, but each mmap/munmap increases a counter
> + * that is checked to determine when has read occurred. If a read
> + * hit SIGSEGV in between mmap/munmap it is a failure. If a read
> + * between mmap/munmap worked, then its value must match expected
> + * value.
> + */
> +#include <errno.h>
> +#include <float.h>
> +#include <pthread.h>
> +#include <sched.h>
> +#include <setjmp.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include "tst_test.h"
> +#include "tst_safe_pthread.h"
> +
> +#define DISTANT_MMAP_SIZE (64*1024*1024)
> +#define TEST_FILENAME "ashfile"
> +
> +/* seconds remaining before reaching timeout */
> +#define STOP_THRESHOLD 10
> +
> +#define PROGRESS_SEC 3
> +
> +static int file_size = 1024;
> +static int num_iter = 5000;
> +static float exec_time = 0.05; /* default is 3 min */
> +
> +static void *distant_area;
> +static char *str_exec_time;
> +static jmp_buf jmpbuf;
> +static volatile unsigned char *map_address;
> +static unsigned long page_sz;
> +
> +static unsigned long mapped_sigsegv_count;
> +static unsigned long map_count;
> +static unsigned long threads_spawned;
> +static unsigned long data_matched;
> +static unsigned long repeated_reads;
> +
> +/* sequence id for each map/unmap performed */
> +static int mapcnt, unmapcnt;
> +/* stored sequence id before making read attempt */
> +static int br_map, br_unmap;
> +
> +static struct tst_option options[] = {
> + {"x:", &str_exec_time, "Exec time (hours)"},
> + {NULL, NULL, NULL}
> +};
> +
> +/* compare "before read" counters with "after read" counters */
> +static inline int was_area_mapped(int br_m, int br_u, int ar_m, int ar_u)
> +{
> + return (br_m == ar_m && br_u == ar_u && br_m > br_u);
> +}

Since the br_map and br_unmap are global I would consider passing only
the values after to this function.

> +static void sig_handler(int signal, siginfo_t *info,
> + LTP_ATTRIBUTE_UNUSED void *ut)
> +{
> + int ar_m, ar_u;
> +
> + switch (signal) {
> + case SIGSEGV:
> + /* if we hit SIGSEGV between map/unmap, something is wrong */
> + ar_u = tst_atomic_load(&unmapcnt);
> + ar_m = tst_atomic_load(&mapcnt);
> + if (was_area_mapped(br_map, br_unmap, ar_m, ar_u)) {
> + tst_res(TFAIL, "got sigsegv while mapped");
> + _exit(TFAIL);
> + }
> +
> + mapped_sigsegv_count++;
> + longjmp(jmpbuf, 1);
> + break;
> + default:
> + tst_res(TFAIL, "Unexpected signal - %d, addr: %p, exiting\n",
> + signal, info->si_addr);
> + _exit(TBROK);
> + }
> +}
> +
> +void *map_write_unmap(void *ptr)
> +{
> + long *args = ptr;
> + void *tmp;
> + int i, j;
> +
> + for (i = 0; i < num_iter; i++) {
> + map_address = SAFE_MMAP(distant_area,
> + (size_t) file_size, PROT_WRITE | PROT_READ,
> + MAP_SHARED, (int)args[0], 0);
> + tst_atomic_inc(&mapcnt);
> +
> + for (j = 0; j < file_size; j++)
> + map_address[j] = 'b';
> +
> + tmp = (void *)map_address;
> + tst_atomic_inc(&unmapcnt);
> + SAFE_MUNMAP(tmp, file_size);
> +
> + map_count++;
> + }
> +
> + return NULL;
> +}
> +
> +void *read_mem(LTP_ATTRIBUTE_UNUSED void *ptr)
> +{
> + int i, j, ar_map, ar_unmap;
> + unsigned char c;
> +
> + for (i = 0; i < num_iter; i++) {
> + if (setjmp(jmpbuf) == 1)
> + continue;
> +
> + for (j = 0; j < file_size; j++) {
> +read_again:
> + br_map = tst_atomic_load(&mapcnt);
> + br_unmap = tst_atomic_load(&unmapcnt);
> +
> + c = map_address[j];
> +
> + ar_unmap = tst_atomic_load(&unmapcnt);
> + ar_map = tst_atomic_load(&mapcnt);
> +
> + /*
> + * Read above is racing against munmap and mmap
> + * in other thread. While the address might be valid
> + * the mapping could be in various stages of being
> + * 'ready'. We only check the value, if we can be sure
> + * read hapenned in between single mmap and munmap as
> + * observed by first thread.
> + */
> + if (was_area_mapped(br_map, br_unmap, ar_map,
> + ar_unmap)) {
> + switch (c) {
> + case 'a':
> + repeated_reads++;
> + goto read_again;
> + case 'b':
> + data_matched++;
> + break;
> + default:
> + tst_res(TFAIL, "value[%d] is %c", j, c);
> + break;
> + }
> + }
> + }
> + }
> +
> + return NULL;
> +}
> +
> +int mkfile(int size)
> +{
> + int fd, i;
> +
> + fd = SAFE_OPEN(TEST_FILENAME, O_RDWR | O_CREAT, 0600);
> + SAFE_UNLINK(TEST_FILENAME);
> +
> + for (i = 0; i < size; i++)
> + SAFE_WRITE(1, fd, "a", 1);
> + SAFE_WRITE(1, fd, "\0", 1);
> +
> + if (fsync(fd) == -1)
> + tst_brk(TBROK | TERRNO, "fsync()");
> +
> + return fd;
> +}
> +
> +static void setup(void)
> +{
> + struct sigaction sigptr;
> +
> + page_sz = getpagesize();
> +
> + /*
> + * Used as hint for mmap thread, so it doesn't interfere
> + * with other potential (temporary) mappings from libc
> + */
> + distant_area = SAFE_MMAP(0, DISTANT_MMAP_SIZE, PROT_WRITE | PROT_READ,
> + MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> + SAFE_MUNMAP(distant_area, (size_t)DISTANT_MMAP_SIZE);
> + distant_area += DISTANT_MMAP_SIZE / 2;
> +
> + if (tst_parse_float(str_exec_time, &exec_time, 0, FLT_MAX)) {
> + tst_brk(TBROK, "Invalid number for exec_time '%s'",
> + str_exec_time);
> + }
> +
> + sigptr.sa_sigaction = sig_handler;
> + sigemptyset(&sigptr.sa_mask);
> + sigptr.sa_flags = SA_SIGINFO | SA_NODEFER;
> + SAFE_SIGACTION(SIGSEGV, &sigptr, NULL);
> +
> + tst_set_timeout((int)(exec_time * 3600));
> +}
> +
> +static void run(void)
> +{
> + pthread_t thid[2];
> + long chld_args[1];
> + int remaining = tst_timeout_remaining();
> + int elapsed = 0;
> +
> + while (tst_timeout_remaining() > STOP_THRESHOLD) {
> + int fd = mkfile(file_size);
> +
> + tst_atomic_store(0, &mapcnt);
> + tst_atomic_store(0, &unmapcnt);
> +
> + chld_args[0] = fd;

I would have just casted the fd here to long or intptr_t (to make sure
compiler padds it with zeroes) then to (void*) and passed the value
directly, i.e. (void*)(inptr_t)fd and then back in the thread we do
fd = (intptr_t)ptr.

> + SAFE_PTHREAD_CREATE(&thid[0], NULL, map_write_unmap, chld_args);
> + SAFE_PTHREAD_CREATE(&thid[1], NULL, read_mem, chld_args);
> + threads_spawned += 2;
> +
> + SAFE_PTHREAD_JOIN(thid[0], NULL);
> + SAFE_PTHREAD_JOIN(thid[1], NULL);
> +
> + close(fd);
> +
> + if (remaining - tst_timeout_remaining() > PROGRESS_SEC) {
> + remaining = tst_timeout_remaining();
> + elapsed += PROGRESS_SEC;
> + tst_res(TINFO, "[%d] mapped: %lu, sigsegv hit: %lu, "
> + "threads spawned: %lu", elapsed, map_count,
> + mapped_sigsegv_count, threads_spawned);
> + tst_res(TINFO, "[%d] repeated_reads: %ld, "
> + "data_matched: %lu", elapsed, repeated_reads,
> + data_matched);
> + }
> + }
> + tst_res(TPASS, "System survived.");
> +}
> +
> +static struct tst_test test = {
> + .test_all = run,
> + .setup = setup,
> + .options = options,
> + .needs_tmpdir = 1,
> +};
> --
> 1.8.3.1
>
>
> --
> Mailing list info: https://lists.linux.it/listinfo/ltp

--
Cyril Hrubis
chrubis@suse.cz