Re: [PATCH 6/6] selftests/liveupdate: add fallocate test for memfd

[Mike Rapoport <rppt@kernel.org>]

On Mon, Mar 09, 2026 at 11:54:39AM +0000, Pratyush Yadav wrote:
> From: "Pratyush Yadav (Google)" <pratyush@kernel.org>
> 
> When memory is added to a memfd via fallocate(), it does not get zeroed
> immediately. This is tracked by the absence of the uptodate folio flag.
> Initially, memfd preservation simply saved the folio flags at preserve
> time. This led to a bug, where all writes to un-initialized fallocated
> memory after preserve were lost after live update. This is fixed by
> patch [0] (not in mainline as of writing this).
> 
> Add a test that fallocates some memory in a memfd, preserves it, writes
> to it. Then in stage 2 it verifies the written content is still present.
> 
> [0] https://lore.kernel.org/linux-mm/20260223173931.2221759-2-pratyush@kernel.org/

Looks like it's already in mm-stable, so it's sha should be stable already.
 
> Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
> ---
>  .../testing/selftests/liveupdate/luo_memfd.c  | 64 +++++++++++++++++++
>  1 file changed, 64 insertions(+)
> 
> diff --git a/tools/testing/selftests/liveupdate/luo_memfd.c b/tools/testing/selftests/liveupdate/luo_memfd.c
> index 75f88101e7b5..dde3c78db50e 100644
> --- a/tools/testing/selftests/liveupdate/luo_memfd.c
> +++ b/tools/testing/selftests/liveupdate/luo_memfd.c
> @@ -43,6 +43,11 @@
>  #define PRESERVED_MEMFD_TOKEN 1
>  #define PRESERVED_BUFFER_SIZE SZ_1M
>  
> +#define FALLOCATE_SESSION_NAME "fallocate_session"
> +#define FALLOCATE_MEMFD_TOKEN 1
> +#define FALLOCATE_BUFFER_SIZE SZ_1M
> +#define RANDOM_DATA_FILE_FALLOCATE "luo_random_data_fallocate.bin"

FILESYSTEM_COPY_ or something like that?

> +
>  #define LIVEUPDATE_DEV "/dev/liveupdate"
>  static int luo_fd = -1, stage;
>  
> @@ -193,6 +198,65 @@ TEST(preserved_ops)
>  	ASSERT_EQ(lseek(fd, 0, SEEK_END), PRESERVED_BUFFER_SIZE);
>  }
>  
> +/*
> + * Test that an fallocated memfd is preserved across live update and can be
> + * written to after being preserved.
> + */
> +TEST(fallocate_memfd)
> +{
> +	int fd, session;
> +	char *buffer;
> +	struct liveupdate_session_preserve_fd preserve_arg = { .size = sizeof(preserve_arg) };
> +	struct liveupdate_session_retrieve_fd retrieve_arg = { .size = sizeof(retrieve_arg) };
> +
> +	buffer = malloc(FALLOCATE_BUFFER_SIZE);
> +	ASSERT_NE(buffer, NULL);
> +
> +	switch (stage) {
> +	case 1:

Functions again :)

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

-- 
Sincerely yours,
Mike.