linux-kernel - Re: [PATCH] selftests/bpf: Fix kmem

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Message-ID: <CABdmKX3QiJupqcHvb9O7Du1h+dVnTAo1D2Upq-Y2dX+XJSk_ng@mail.gmail.com>
Date: Mon, 28 Apr 2025 20:00:25 -0700
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/bpf: Fix kmem_cache iterator draining

On Mon, Apr 28, 2025 at 1:06 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Hello,
>
> On Mon, Apr 28, 2025 at 06:02:54PM +0000, T.J. Mercier wrote:
> > The closing parentheses around the read syscall is misplaced, causing
> > single byte reads from the iterator instead of buf sized reads. While
> > the end result is the same, many more read calls than necessary are
> > performed.
> >
> > $ tools/testing/selftests/bpf/vmtest.sh  "./test_progs -t kmem_cache_iter"
> > 145/1   kmem_cache_iter/check_task_struct:OK
> > 145/2   kmem_cache_iter/check_slabinfo:OK
> > 145/3   kmem_cache_iter/open_coded_iter:OK
> > 145     kmem_cache_iter:OK
> > Summary: 1/3 PASSED, 0 SKIPPED, 0 FAILED
> >
> > Fixes: a496d0cdc84d ("selftests/bpf: Add a test for kmem_cache_iter")
> > Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
>
> Oops, thanks for fixing this.
>
> Acked-by: Namhyung Kim <namhyung@...nel.org>
>
> Thanks,
> Namhyung

No worries, thanks! It's been helpful reading through this code.

> > ---
> >  tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> > index 8e13a3416a21..1de14b111931 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c
> > @@ -104,7 +104,7 @@ void test_kmem_cache_iter(void)
> >               goto destroy;
> >
> >       memset(buf, 0, sizeof(buf));
> > -     while (read(iter_fd, buf, sizeof(buf) > 0)) {
> > +     while (read(iter_fd, buf, sizeof(buf)) > 0) {
> >               /* Read out all contents */
> >               printf("%s", buf);
> >       }
> >
> > base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e
> > --
> > 2.49.0.906.g1f30a19c02-goog
> >