linux-kernel - Re: [PATCH v2 4/6] selftests/mm: refactor uffd_poll

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Message-ID: <ZKSJNB3BbCiPxcdD@x1n>
Date:   Tue, 4 Jul 2023 17:03:48 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <brauner@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Huang Ying <ying.huang@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        James Houghton <jthoughton@...gle.com>,
        Jiaqi Yan <jiaqiyan@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Nadav Amit <namit@...are.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Shuah Khan <shuah@...nel.org>,
        ZhangPeng <zhangpeng362@...wei.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 4/6] selftests/mm: refactor uffd_poll_thread to allow
 custom fault handlers

On Thu, Jun 29, 2023 at 01:50:38PM -0700, Axel Rasmussen wrote:
> Previously, we had "one fault handler to rule them all", which used
> several branches to deal with all of the scenarios required by all of
> the various tests.
> 
> In upcoming patches, I plan to add a new test, which has its own
> slightly different fault handling logic. Instead of continuing to add
> cruft to the existing fault handler, let's allow tests to define custom
> ones, separate from other tests.
> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> ---
>  tools/testing/selftests/mm/uffd-common.c |  5 ++++-
>  tools/testing/selftests/mm/uffd-common.h |  3 +++
>  tools/testing/selftests/mm/uffd-stress.c | 12 +++++++-----
>  3 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c
> index ba20d7504022..02b89860e193 100644
> --- a/tools/testing/selftests/mm/uffd-common.c
> +++ b/tools/testing/selftests/mm/uffd-common.c
> @@ -499,6 +499,9 @@ void *uffd_poll_thread(void *arg)
>  	int ret;
>  	char tmp_chr;
>  
> +	if (!args->handle_fault)
> +		args->handle_fault = uffd_handle_page_fault;
> +
>  	pollfd[0].fd = uffd;
>  	pollfd[0].events = POLLIN;
>  	pollfd[1].fd = pipefd[cpu*2];
> @@ -527,7 +530,7 @@ void *uffd_poll_thread(void *arg)
>  			err("unexpected msg event %u\n", msg.event);
>  			break;
>  		case UFFD_EVENT_PAGEFAULT:
> -			uffd_handle_page_fault(&msg, args);
> +			args->handle_fault(&msg, args);
>  			break;
>  		case UFFD_EVENT_FORK:
>  			close(uffd);
> diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h
> index 197f5262fe0d..7c4fa964c3b0 100644
> --- a/tools/testing/selftests/mm/uffd-common.h
> +++ b/tools/testing/selftests/mm/uffd-common.h
> @@ -77,6 +77,9 @@ struct uffd_args {
>  	unsigned long missing_faults;
>  	unsigned long wp_faults;
>  	unsigned long minor_faults;
> +
> +	/* A custom fault handler; defaults to uffd_handle_page_fault. */
> +	void (*handle_fault)(struct uffd_msg *msg, struct uffd_args *args);
>  };
>  
>  struct uffd_test_ops {
> diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
> index 995ff13e74c7..50b1224d72c7 100644
> --- a/tools/testing/selftests/mm/uffd-stress.c
> +++ b/tools/testing/selftests/mm/uffd-stress.c
> @@ -189,10 +189,8 @@ static int stress(struct uffd_args *args)
>  				   locking_thread, (void *)cpu))
>  			return 1;
>  		if (bounces & BOUNCE_POLL) {
> -			if (pthread_create(&uffd_threads[cpu], &attr,
> -					   uffd_poll_thread,
> -					   (void *)&args[cpu]))
> -				return 1;
> +			if (pthread_create(&uffd_threads[cpu], &attr, uffd_poll_thread, &args[cpu]))
> +				err("uffd_poll_thread create");

irrelevant change?

>  		} else {
>  			if (pthread_create(&uffd_threads[cpu], &attr,
>  					   uffd_read_thread,
> @@ -247,9 +245,13 @@ static int userfaultfd_stress(void)
>  {
>  	void *area;
>  	unsigned long nr;
> -	struct uffd_args args[nr_cpus];
> +	struct uffd_args *args;
>  	uint64_t mem_size = nr_pages * page_size;
>  
> +	args = calloc(nr_cpus, sizeof(struct uffd_args));
> +	if (!args)
> +		err("allocating args array failed");
> +

It's leaked?

Isn't "args[] = { 0 }" already working?

Thanks,

>  	if (uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED, NULL))
>  		err("context init failed");
>  
> -- 
> 2.41.0.255.g8b1d071c50-goog
> 

-- 
Peter Xu