[LTP] [PATCH v3 2/7] tst_atomic: Add atomic store and load tests

[Cyril Hrubis]

Hi!
> diff --git a/lib/newlib_tests/test15.c b/lib/newlib_tests/test15.c
> new file mode 100644
> index 000000000..ba3cc963f
> --- /dev/null
> +++ b/lib/newlib_tests/test15.c
> @@ -0,0 +1,132 @@
> +/*
> + * Copyright (c) 2017 Richard Palethorpe <rpalethorpe@suse.com>
> + *
> + * This program is free software: you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation, either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +/*
> + * A basic regression test for tst_atomic_{load,store}. Also provides a
> + * limited check that atomic stores and loads order non-atomic memory
> + * accesses. That is, we are checking that they implement memory fences or
> + * barriers.
> + *
> + * Many architectures/machines will still pass the test even if you remove the
> + * atomic functions. X86 in particular has strong memory ordering by default
> + * so that should always pass (if you use volatile). However Aarch64
> + * (Raspberry Pi 3 Model B) has been observed to fail without the atomic
> + * functions.
> + *
> + * A failure can occur if an update to seq_n is not made globally visible by
> + * the time the next thread needs to use it.
> + */
> +
> +#include <stdint.h>
> +#include <pthread.h>
> +#include "tst_test.h"
> +#include "tst_atomic.h"
> +
> +#define THREADS 64
> +#define FILLER (1 << 20)
> +
> +/* Uncomment these to see what happens without atomics. To prevent the compiler
> + * from removing/reording atomic and seq_n, mark them as volatile.
> + */
> +/* #define tst_atomic_load(v) (*(v)) */
> +/* #define tst_atomic_store(i, v) *(v) = (i) */
> +
> +struct block {
> +	int seq_n;
> +	intptr_t id;
> +	intptr_t filler[FILLER];
> +};
> +
> +static int atomic;
> +static int *seq_n;
> +static struct block *m;
> +
> +static void *worker_load_store(void *_id)
> +{
> +	intptr_t id = (intptr_t)_id, i;

You can do:
	int id = (intptr_t)_id, i;

Then you can drop the casts int the rest of the function.

Also identifiers starting with underscore or two are reserved for system
libraries (libc/kernel headers).

> +	for (i = (intptr_t)tst_atomic_load(&atomic);
> +	     i != id;
> +	     i = (intptr_t)tst_atomic_load(&atomic))
> +		;

Okay this spins in place until atomic == id, hence only one thread gets
to run the code below and they should get there in increasing order by
id.

> +	(m + (*seq_n))->id = id;
> +	*seq_n += 1;

But I do not get why seq_n points in the middle of the mmaped area. A
short comment on the expected efect of this as well as of the cache
ruiner would help a bit.

> +	tst_atomic_store((int)i + 1, &atomic);
> +
> +	return NULL;
> +}
> +
> +static void *cache_ruiner(void *vp LTP_ATTRIBUTE_UNUSED)
> +{
> +	intptr_t i = 0, j;
> +	struct block *cur = m;
> +
> +	tst_res(TINFO, "cache ruiner started");
> +	while (tst_atomic_load(&atomic) > 0) {
> +		for (j = 0; j < FILLER; j++)
> +			cur->filler[j] = j;
> +
> +		if (i < THREADS - 1) {
> +			cur = m + (++i);
> +		} else {
> +			i = 0;
> +			cur = m;
> +		}

		i = (i + 1) % (THREADS - 1);
		cur = m + i;

> +	}
> +
> +	return NULL;
> +}
> +
> +static void do_test(void)
> +{
> +	intptr_t i, id;
> +	pthread_t threads[THREADS + 1];
> +
> +	atomic = 0;
> +	m = (struct block *)SAFE_MMAP(NULL, sizeof(*m) * THREADS,
              ^
	      Useless cast.
> +				      PROT_READ | PROT_WRITE,
> +				      MAP_PRIVATE | MAP_ANONYMOUS,
> +				      -1, 0);
> +	seq_n = &((m + THREADS / 2)->seq_n);
> +
> +	pthread_create(threads+THREADS, NULL, cache_ruiner, NULL);
> +	for (i = THREADS - 1; i >= 0; i--)
> +		pthread_create(threads+i, NULL, worker_load_store, (void *)i);
> +
> +	for (i = 0; i < THREADS; i++) {
> +		tst_res(TINFO, "Joining thread %li", i);
> +		pthread_join(threads[i], NULL);
> +	}
> +	tst_atomic_store(-1, &atomic);
> +	pthread_join(*(threads+THREADS), NULL);
                      ^
		      Huh, why not just threads[THREADS] ?
> +
> +	tst_res(TINFO, "Expected\tFound");
> +	for (i = 0; i < THREADS; i++) {
> +		id = (m + i)->id;
> +		if (id != i)
> +			tst_res(TFAIL, "%d\t\t%d", (int)i, (int)id);
> +		else
> +			tst_res(TPASS, "%d\t\t%d", (int)i, (int)id);
> +	}
> +
> +	SAFE_MUNMAP(m, sizeof(*m) * THREADS);
> +}
> +
> +static struct tst_test test = {
> +	.test_all = do_test,
> +};
> -- 
> 2.14.1
> 
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp

-- 
Cyril Hrubis
chrubis@suse.cz