Message-ID: <87tt41nydl.ffs@tglx>
Date: Fri, 27 Jun 2025 14:48:54 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: André Almeida <andrealmeid@...lia.com>, Ingo Molnar
 <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>, Shuah Khan <shuah@...nel.org>, Arnd
 Bergmann <arnd@...db.de>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>, Waiman Long <longman@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-api@...r.kernel.org, kernel-dev@...lia.com, André
 Almeida
 <andrealmeid@...lia.com>
Subject: Re: [PATCH v5 7/7] selftests: futex: Expand robust list test for
 the new interface

On Thu, Jun 26 2025 at 14:11, André Almeida wrote:

> Expand the current robust list test for the new set_robust_list2
> syscall. Create an option to make it possible to run the same tests
> using the new syscall, and also add two new relevant test: test long
> lists (bigger than ROBUST_LIST_LIMIT) and for unaligned addresses.
>
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
>  .../selftests/futex/functional/robust_list.c       | 160 ++++++++++++++++++++-
>  1 file changed, 156 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/futex/functional/robust_list.c b/tools/testing/selftests/futex/functional/robust_list.c
> index 42690b2440fd29a9b12c46f67f9645ccc93d1147..004ad79ff6171c411fd47e699e3c38889544218e 100644
> --- a/tools/testing/selftests/futex/functional/robust_list.c
> +++ b/tools/testing/selftests/futex/functional/robust_list.c
> @@ -35,16 +35,45 @@
>  #include <stddef.h>
>  #include <sys/mman.h>
>  #include <sys/wait.h>
> +#include <stdint.h>
>  
>  #define STACK_SIZE (1024 * 1024)
>  
>  #define FUTEX_TIMEOUT 3
>  
> +#define SYS_set_robust_list2 468
> +
> +enum robust_list2_type {
> +        ROBUST_LIST_32BIT,
> +        ROBUST_LIST_64BIT,
> +};

Why can't this use an updated header?

> +
>  static pthread_barrier_t barrier, barrier2;
>  
> +bool robust2 = false;

global because ....

>  int set_robust_list(struct robust_list_head *head, size_t len)
>  {
> -	return syscall(SYS_set_robust_list, head, len);
> +	int ret, flags;
> +
> +	if (!robust2) {
> +		return syscall(SYS_set_robust_list, head, len);
> +	}

Pointless brackets.

> +	if (sizeof(head) == 8)
> +		flags = ROBUST_LIST_64BIT;
> +	else
> +		flags = ROBUST_LIST_32BIT;
> +
> +	/*
> +	 * We act as we have just one list here. We try to use the first slot,
> +	 * but if it hasn't been alocated yet we allocate it.
> +	 */
> +	ret = syscall(SYS_set_robust_list2, head, 0, flags);
> +	if (ret == -1 && errno == ENOENT)
> +		ret = syscall(SYS_set_robust_list2, head, -1, flags);

What the heck is this?

> +	return ret;
>  }
>  
>  int get_robust_list(int pid, struct robust_list_head **head, size_t *len_ptr)
> @@ -246,6 +275,11 @@ static void test_set_robust_list_invalid_size(void)
>  	size_t head_size = sizeof(struct robust_list_head);
>  	int ret;
>  
> +	if (robust2) {
> +		ksft_test_result_skip("This test is only for old robust interface\n");

Why is it invoked in the first place?

> +		return;
> +	}
> +
>  	ret = set_robust_list(&head, head_size);
>  	ASSERT_EQ(ret, 0);
>  
> @@ -321,6 +355,11 @@ static void test_get_robust_list_child(void)
>  	struct robust_list_head head, *get_head;
>  	size_t len_ptr;
>  
> +	if (robust2) {
> +		ksft_test_result_skip("Not implemented in the new robust interface\n");

For the very wrong reasons.

> +		return;
> +	}
> +
>  	ret = pthread_barrier_init(&barrier, NULL, 2);
>  	ret = pthread_barrier_init(&barrier2, NULL, 2);
>  	ASSERT_EQ(ret, 0);
> @@ -332,7 +371,7 @@ static void test_get_robust_list_child(void)
>  
>  	ret = get_robust_list(tid, &get_head, &len_ptr);
>  	ASSERT_EQ(ret, 0);
> -	ASSERT_EQ(&head, get_head);
> +	ASSERT_EQ(get_head, &head);

ROTFL

>  
>  	pthread_barrier_wait(&barrier2);
>  
> @@ -507,11 +546,119 @@ static void test_circular_list(void)
>  	ksft_test_result_pass("%s\n", __func__);
>  }
>  
> +#define ROBUST_LIST_LIMIT	2048
> +#define CHILD_LIST_LIMIT (ROBUST_LIST_LIMIT + 10)
> +
> +static int child_robust_list_limit(void *arg)
> +{
> +	struct lock_struct *locks;
> +	struct robust_list *list;
> +	struct robust_list_head head;
> +	int ret, i;
> +
> +	locks = (struct lock_struct *) arg;
> +
> +	ret = set_list(&head);
> +	if (ret)
> +		ksft_test_result_fail("set_list error\n");

Yet again the same broken crap.

> +	/*
> +	 * Create a very long list of locks
> +	 */
> +	head.list.next = &locks[0].list;
> +
> +	list = head.list.next;
> +	for (i = 0; i < CHILD_LIST_LIMIT - 1; i++) {
> +		list->next = &locks[i+1].list;
> +		list = list->next;
> +	}
> +	list->next = &head.list;
> +
> +	/*
> +	 * Grab the lock in the last one, and die without releasing it
> +	 */
> +	mutex_lock(&locks[CHILD_LIST_LIMIT], &head, false);
> +	pthread_barrier_wait(&barrier);
> +
> +	sleep(1);
> +
> +	return 0;
> +}
> +
> +/*
> + * The old robust list used to have a limit of 2048 items from the kernel side.
> + * After this limit the kernel stops walking the list and ignore the other

ignores

> + * futexes, causing deadlocks.
> + *
> + * For the new interface, test if we can wait for a list of more than 2048
> + * elements.
> + */
> +static void test_robust_list_limit(void)
> +{
> +	struct lock_struct locks[CHILD_LIST_LIMIT + 1];
> +	_Atomic(unsigned int) *futex = &locks[CHILD_LIST_LIMIT].futex;
> +	struct robust_list_head head;
> +	int ret;
> +
> +	if (!robust2) {
> +		ksft_test_result_skip("This test is only for new robust interface\n");
> +		return;
> +	}
> +
> +	*futex = 0;
> +
> +	ret = set_list(&head);
> +	ASSERT_EQ(ret, 0);
> +
> +	ret = pthread_barrier_init(&barrier, NULL, 2);
> +	ASSERT_EQ(ret, 0);
> +
> +	create_child(child_robust_list_limit, locks);
> +
> +	/*
> +	 * After the child thread creates the very long list of locks, wait on
> +	 * the last one.
> +	 */
> +	pthread_barrier_wait(&barrier);
> +	ret = mutex_lock(&locks[CHILD_LIST_LIMIT], &head, false);
> +
> +	if (ret != 0)
> +		printf("futex wait returned %d\n", errno);
> +	ASSERT_EQ(ret, 0);

lalala.

> +
> +	ASSERT_TRUE(*futex | FUTEX_OWNER_DIED);

Copy and pasta does not make it more correct.

> +	wait(NULL);
> +	pthread_barrier_destroy(&barrier);
> +
> +	ksft_test_result_pass("%s\n", __func__);
> +}
> +
> +/*
> + * The kernel should refuse an unaligned head pointer
> + */
> +static void test_unaligned_address(void)
> +{
> +	struct robust_list_head head, *h;
> +	int ret;
> +
> +	if (!robust2) {
> +		ksft_test_result_skip("This test is only for new robust interface\n");
> +		return;
> +	}
> +
> +	h = (struct robust_list_head *) ((uintptr_t) &head + 1);
> +	ret = set_list(h);
> +	ASSERT_EQ(ret, -1);
> +	ASSERT_EQ(errno, EINVAL);
> +}
> +
>  void usage(char *prog)
>  {
>  	printf("Usage: %s\n", prog);
>  	printf("  -c	Use color\n");
>  	printf("  -h	Display this help message\n");
> +	printf("  -n	Use robust2 syscall\n");

Right. We need a command line option to guarantee that the test is not
executed by bots...

>  	printf("  -v L	Verbosity level: %d=QUIET %d=CRITICAL %d=INFO\n",
>  	       VQUIET, VCRITICAL, VINFO);
>  }
> @@ -520,7 +667,7 @@ int main(int argc, char *argv[])
>  {
>  	int c;
>  
> -	while ((c = getopt(argc, argv, "cht:v:")) != -1) {
> +	while ((c = getopt(argc, argv, "chnt:v:")) != -1) {
>  		switch (c) {
>  		case 'c':
>  			log_color(1);
> @@ -531,6 +678,9 @@ int main(int argc, char *argv[])
>  		case 'v':
>  			log_verbosity(atoi(optarg));
>  			break;
> +		case 'n':
> +			robust2 = true;
> +			break;
>  		default:
>  			usage(basename(argv[0]));
>  			exit(1);
> @@ -538,7 +688,7 @@ int main(int argc, char *argv[])
>  	}
>  
>  	ksft_print_header();
> -	ksft_set_plan(7);
> +	ksft_set_plan(8);
>

Just check whether the new syscall is implemented and then set the
number of tests accordingly.

>  	test_robustness();
>  
> @@ -548,6 +698,8 @@ int main(int argc, char *argv[])
>  	test_set_list_op_pending();
>  	test_robust_list_multiple_elements();
>  	test_circular_list();
> +	test_robust_list_limit();
> +	test_unaligned_address();

and then do:

	test_robustness();
        ....
	test_circular_list();

        if (has_robust) {
        	robust2 = true;
                
                test_robustness();
                ...
                test_circular_list();
		test_robust_list_limit();
		test_unaligned_address();
                
        }        

or something like that.

Time for a stiff drink....

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