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Message-ID: <20501a7c-19f6-4154-aebc-49df04c9b043@redhat.com>
Date:   Mon, 17 Jul 2023 19:40:09 +0200
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To:     Ryan Roberts <ryan.roberts@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Mark Brown <broonie@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Florent Revest <revest@chromium.org>,
        Peter Xu <peterx@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org
References: <20230717103152.202078-1-ryan.roberts@arm.com>
 <20230717103152.202078-7-ryan.roberts@arm.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Subject: Re: [PATCH v2 6/8] selftests/mm: Make migration test robust to
 failure
In-Reply-To: <20230717103152.202078-7-ryan.roberts@arm.com>
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On 17.07.23 12:31, Ryan Roberts wrote:
> The `migration` test currently has a number of robustness problems that
> cause it to hang and leak resources.
> 
> Timeout: There are 3 tests, which each previously ran for 60 seconds.
> However, the timeout in mm/settings for a single test binary was set to
> 45 seconds. So when run using run_kselftest.sh, the top level timeout
> would trigger before the test binary was finished. Solve this by meeting
> in the middle; each of the 3 tests now runs for 20 seconds (for a total
> of 60), and the top level timeout is set to 90 seconds.
> 
> Leaking child processes: the `shared_anon` test fork()s some children
> but then an ASSERT() fires before the test kills those children. The
> assert causes immediate exit of the parent and leaking of the children.
> Furthermore, if run using the run_kselftest.sh wrapper, the wrapper
> would get stuck waiting for those children to exit, which never happens.
> Solve this by deferring any asserts until after the children are killed.
> The same pattern is used for the threaded tests for uniformity.
> 
> With these changes, the test binary now runs to completion on arm64,
> with 2 tests passing and the `shared_anon` test failing.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>   tools/testing/selftests/mm/migration.c | 14 ++++++++++----
>   tools/testing/selftests/mm/settings    |  2 +-
>   2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/migration.c b/tools/testing/selftests/mm/migration.c
> index 379581567f27..189d7d9070e8 100644
> --- a/tools/testing/selftests/mm/migration.c
> +++ b/tools/testing/selftests/mm/migration.c
> @@ -15,7 +15,7 @@
>   #include <time.h>
>   
>   #define TWOMEG (2<<20)
> -#define RUNTIME (60)
> +#define RUNTIME (20)
>   
>   #define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
>   
> @@ -118,6 +118,7 @@ TEST_F_TIMEOUT(migration, private_anon, 2*RUNTIME)
>   {
>   	uint64_t *ptr;
>   	int i;
> +	int ret;
>   
>   	if (self->nthreads < 2 || self->n1 < 0 || self->n2 < 0)
>   		SKIP(return, "Not enough threads or NUMA nodes available");
> @@ -131,9 +132,10 @@ TEST_F_TIMEOUT(migration, private_anon, 2*RUNTIME)
>   		if (pthread_create(&self->threads[i], NULL, access_mem, ptr))
>   			perror("Couldn't create thread");
>   
> -	ASSERT_EQ(migrate(ptr, self->n1, self->n2), 0);
> +	ret = migrate(ptr, self->n1, self->n2);
>   	for (i = 0; i < self->nthreads - 1; i++)
>   		ASSERT_EQ(pthread_cancel(self->threads[i]), 0);
> +	ASSERT_EQ(ret, 0);

Why is that required? This does not involve fork.

>   }
>   
>   /*
> @@ -144,6 +146,7 @@ TEST_F_TIMEOUT(migration, shared_anon, 2*RUNTIME)
>   	pid_t pid;
>   	uint64_t *ptr;
>   	int i;
> +	int ret;
>   
>   	if (self->nthreads < 2 || self->n1 < 0 || self->n2 < 0)
>   		SKIP(return, "Not enough threads or NUMA nodes available");
> @@ -161,9 +164,10 @@ TEST_F_TIMEOUT(migration, shared_anon, 2*RUNTIME)
>   			self->pids[i] = pid;
>   	}
>   
> -	ASSERT_EQ(migrate(ptr, self->n1, self->n2), 0);
> +	ret = migrate(ptr, self->n1, self->n2);
>   	for (i = 0; i < self->nthreads - 1; i++)
>   		ASSERT_EQ(kill(self->pids[i], SIGTERM), 0);
> +	ASSERT_EQ(ret, 0);


Might be cleaner to also:

diff --git a/tools/testing/selftests/mm/migration.c 
b/tools/testing/selftests/mm/migration.c
index 379581567f27..b3f12b9847ec 100644
--- a/tools/testing/selftests/mm/migration.c
+++ b/tools/testing/selftests/mm/migration.c
@@ -11,6 +11,7 @@
  #include <numaif.h>
  #include <sys/mman.h>
  #include <sys/types.h>
+#include <sys/prctl.h>
  #include <signal.h>
  #include <time.h>

@@ -155,10 +156,12 @@ TEST_F_TIMEOUT(migration, shared_anon, 2*RUNTIME)
         memset(ptr, 0xde, TWOMEG);
         for (i = 0; i < self->nthreads - 1; i++) {
                 pid = fork();
-               if (!pid)
+               if (!pid) {
+                       prctl(PR_SET_PDEATHSIG, SIGHUP);
                         access_mem(ptr);
-               else
+               } else {
                         self->pids[i] = pid;
+               }
         }

         ASSERT_EQ(migrate(ptr, self->n1, self->n2), 0);


Then, whenever the parent dies, all child processes get zapped.


-- 
Cheers,

David / dhildenb