On Wed, 27 May 2026 17:54:37 +0800
Tianchen Ding <[email protected]> wrote:
> On ARM64 kernels with 64K pages, the trace_marker_raw test fails because
> bash's printf builtin uses stdio buffering which splits output into
> multiple small write() calls to the tracefs file. Since each individual
> write is within TRACE_MARKER_MAX_SIZE (4096), they all succeed, causing
> the "too big" write test to incorrectly pass.
>
> Fix by piping make_str output through dd with iflag=fullblock to
> guarantee a single atomic write() syscall to trace_marker_raw.
>
> Fixes: 37f46601383a ("selftests/tracing: Add basic test for trace_marker_raw
> file")
> Signed-off-by: Tianchen Ding <[email protected]>
> ---
> .../selftests/ftrace/test.d/00basic/trace_marker_raw.tc | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git
> a/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
> b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
> index 8e905d4fe6dd..efd8263e6087 100644
> --- a/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
> +++ b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
> @@ -43,8 +43,10 @@ write_buffer() {
> id=$1
> size=$2
>
> - # write the string into the raw marker
> - make_str $id $size > trace_marker_raw
> + # Pipe through dd to ensure a single atomic write() syscall.
> + # Shell's printf builtin uses stdio buffering which may split the
> + # output into multiple writes.
Could you comment that this is for architectures with 64K pages too.
Thanks for fixing this,
-- Steve
> + make_str $id $size | dd of=trace_marker_raw bs=`expr $size + 4`
> iflag=fullblock
> }
>
>
