Re: [PATCH] selftests/mm: pkeys: wait for the child in become_child()

[Andrew Morton]

On Fri,  6 Nov 2026 17:46:39 +0100 Carlos López <clopez@xxxxxxx> wrote:

> become_child() forks during test_pkey_alloc_exhaust() and has the parent
> exit, so that the remaining tests run in the child. However, the test
> runner only waits for the original process, so it sees the test finish
> early with a success status while the remaining tests keep running in
> the background. Failures after the first fork are thus not reported in
> the exit status, and the remaining tests overlap with the next selftest.
> 
> Fix this by waiting for the child in the parent and exiting with its
> status. A previous fix avoided waiting, arguing that the parents would
> keep holding their resources [1]. Particularly, the parent keeps the
> hugetlb reservation of its test memory, so the child runs out of hugetlb
> pages after a few iterations. Avoid this by freeing the test memory
> before waiting.

Thanks.

>  tools/testing/selftests/mm/protection_keys.c | 16 +++++++++++++---

get_maintainer coverage of selftests is poor, alas.  So it's a good
idea to poke around in the git-blame output to figure out who best to
cc.  I added four new lucky duckies to this thread.

> --- a/tools/testing/selftests/mm/protection_keys.c
> +++ b/tools/testing/selftests/mm/protection_keys.c
> @@ -1009,9 +1009,10 @@ static void test_pkey_syscalls_bad_args(int *ptr, u16 pkey)
>  	pkey_assert(err);
>  }
>  
> -static void become_child(void)
> +static void become_child(int *ptr)
>  {
>  	pid_t forkret;
> +	int status;
>  
>  	forkret = fork();
>  	pkey_assert(forkret >= 0);
> @@ -1021,7 +1022,16 @@ static void become_child(void)
>  		/* in the child */
>  		return;
>  	}
> -	_exit(0);
> +
> +	/*
> +	 * Wait for the child to finish the tests and pass on its result.
> +	 * Free the test memory first, as it may reserve pages from the
> +	 * small hugetlb pool that the child needs.
> +	 */
> +	free_pkey_malloc(ptr);
> +	if (waitpid(forkret, &status, 0) != forkret || !WIFEXITED(status))
> +		_exit(KSFT_FAIL);
> +	_exit(WEXITSTATUS(status));
>  }
>  
>  /* Assumes that all pkeys other than 'pkey' are unallocated */
> @@ -1060,7 +1070,7 @@ static void test_pkey_alloc_exhaust(int *ptr, u16 pkey)
>  		 * preserved across fork().
>  		 */
>  		if (i == NR_PKEYS*2)
> -			become_child();
> +			become_child(ptr);
>  	}
>  
>  	dprintf3("%s()::%d\n", __func__, __LINE__);
> 

Looks good, checks out, I'll queue it up.