linux-kernel - Re: [PATCH v1] selftests/mm: fix charge_reserved

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Message-ID: <CAHS8izNyDymXoH94usJTGNHG45HB50m7SSkL6H1C+9pxBEDE+g@mail.gmail.com>
Date: Wed, 21 Aug 2024 11:59:11 -0400
From: Mina Almasry <almasrymina@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	linux-kselftest@...r.kernel.org, Mario Casquero <mcasquer@...hat.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>, 
	Muchun Song <muchun.song@...ux.dev>
Subject: Re: [PATCH v1] selftests/mm: fix charge_reserved_hugetlb.sh test

On Wed, Aug 21, 2024 at 8:31 AM David Hildenbrand <david@...hat.com> wrote:
>
> Currently, running the charge_reserved_hugetlb.sh selftest we can
> sometimes observe something like:
>
>   $ ./charge_reserved_hugetlb.sh -cgroup-v2
>   ...
>   write_result is 0
>   After write:
>   hugetlb_usage=0
>   reserved_usage=10485760
>   killing write_to_hugetlbfs
>   Received 2.
>   Deleting the memory
>   Detach failure: Invalid argument
>   umount: /mnt/huge: target is busy.
>
> Both cases are issues in the test.
>
> While the unmount error seems to be racy, it will make the test fail:
>         $ ./run_vmtests.sh -t hugetlb
>         ...
>         # [FAIL]
>         not ok 10 charge_reserved_hugetlb.sh -cgroup-v2 # exit=32
>
> The issue is that we are not waiting for the write_to_hugetlbfs process
> to quit. So it might still have a hugetlbfs file open, about which
> umount is not happy. Fix that by making "killall" wait for the process
> to quit.
>
> The other error ("Detach failure: Invalid argument") does not seem to
> result in a test error, but is misleading. Turns out write_to_hugetlbfs.c
> unconditionally tries to cleanup using shmdt(), even when we only
> mmap()'ed a hugetlb file. Even worse, shmaddr is never even set for the
> SHM case. Fix that as well.
>
> With this change it seems to work as expected.
>
> Fixes: 29750f71a9b4 ("hugetlb_cgroup: add hugetlb_cgroup reservation tests")
> Reported-by: Mario Casquero <mcasquer@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Muchun Song <muchun.song@...ux.dev>
> Cc: Mina Almasry <almasrymina@...gle.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Initially I thought it could be nice to split fixes for the 2 issues
in separate patches in case one of them ends up needing a revert or
something, but probably not worth a respin. Fixes look good to me.

Reviewed-by: Mina Almasry <almasrymina@...gle.com>

> ---
>  .../selftests/mm/charge_reserved_hugetlb.sh   |  2 +-
>  .../testing/selftests/mm/write_to_hugetlbfs.c | 21 +++++++++++--------
>  2 files changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> index d680c00d2853a..67df7b47087f0 100755
> --- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> +++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> @@ -254,7 +254,7 @@ function cleanup_hugetlb_memory() {
>    local cgroup="$1"
>    if [[ "$(pgrep -f write_to_hugetlbfs)" != "" ]]; then
>      echo killing write_to_hugetlbfs
> -    killall -2 write_to_hugetlbfs
> +    killall -2 --wait write_to_hugetlbfs

This looks correct. I don't think I expected killall not to wait.

>      wait_for_hugetlb_memory_to_get_depleted $cgroup
>    fi
>    set -e
> diff --git a/tools/testing/selftests/mm/write_to_hugetlbfs.c b/tools/testing/selftests/mm/write_to_hugetlbfs.c
> index 6a2caba19ee1d..1289d311efd70 100644
> --- a/tools/testing/selftests/mm/write_to_hugetlbfs.c
> +++ b/tools/testing/selftests/mm/write_to_hugetlbfs.c
> @@ -28,7 +28,7 @@ enum method {
>
>  /* Global variables. */
>  static const char *self;
> -static char *shmaddr;
> +static int *shmaddr;
>  static int shmid;
>
>  /*
> @@ -47,15 +47,17 @@ void sig_handler(int signo)
>  {
>         printf("Received %d.\n", signo);
>         if (signo == SIGINT) {
> -               printf("Deleting the memory\n");
> -               if (shmdt((const void *)shmaddr) != 0) {
> -                       perror("Detach failure");
> +               if (shmaddr) {
> +                       printf("Deleting the memory\n");
> +                       if (shmdt((const void *)shmaddr) != 0) {
> +                               perror("Detach failure");
> +                               shmctl(shmid, IPC_RMID, NULL);
> +                               exit(4);
> +                       }
> +
>                         shmctl(shmid, IPC_RMID, NULL);
> -                       exit(4);
> +                       printf("Done deleting the memory\n");
>                 }
> -
> -               shmctl(shmid, IPC_RMID, NULL);
> -               printf("Done deleting the memory\n");

This seems like a simple refactor to only delete when shmaddr is set,
looks fine to me.

>         }
>         exit(2);
>  }
> @@ -211,7 +213,8 @@ int main(int argc, char **argv)
>                         shmctl(shmid, IPC_RMID, NULL);
>                         exit(2);
>                 }
> -               printf("shmaddr: %p\n", ptr);
> +               shmaddr = ptr;
> +               printf("shmaddr: %p\n", shmaddr);
>

Setting shmaddr seems correct and an oversight. I don't see shmaddr
set anywhere in the current code.

>                 break;
>         default:
> --
> 2.46.0
>


-- 
Thanks,
Mina