linux-kernel - [PATCH] selftests/nolibc: test

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Date:   Fri,  2 Jun 2023 10:41:57 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     falcon@...ylab.org, thomas@...ch.de, w@....eu
Cc:     linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: [PATCH] selftests/nolibc: test_fork: fix up duplicated print

Hi, Willy

What about this one for 2023xxxx-nolibc-rv32+stkp6?

@Thomas, welcome your Reviewed-by If it is ok for you ;-)

Best regards,
Zhangjin

> running nolibc-test with glibc on x86_64 got such print issue:
> 
>     29 execve_root = -1 EACCES                                       [OK]
>     30 fork30 fork = 0                                                      [OK]
>     31 getdents64_root = 712                                         [OK]
> 
> The fork test case has three printf calls:
> 
>     (1) llen += printf("%d %s", test, #name);
>     (2) llen += printf(" = %d %s ", expr, errorname(errno));
>     (3) llen += pad_spc(llen, 64, "[FAIL]\n"); --> vfprintf()
> 
> In the following scene, the above issue happens:
> 
>     (a) The parent calls (1)
>     (b) The parent calls fork()
>     (c) The child runs and shares the print buffer of (1)
>     (d) The child exits, flushs the print buffer and closes its own stdout/stderr
>         * "30 fork" is printed at the first time.
>     (e) The parent calls (2) and (3), with "\n" in (3), it flushs the whole buffer
>         * "30 fork = 0 ..." is printed
> 
> Therefore, there are two "30 fork" in the stdout.
> 
> Between (a) and (b), if flush the stdout (and the sterr), the child in
> stage (c) will not be able to 'see' the print buffer.
> 
> Signed-off-by: Zhangjin Wu <falcon@...ylab.org>
> ---
>  tools/testing/selftests/nolibc/nolibc-test.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> index 7de46305f419..88323a60aa4a 100644
> --- a/tools/testing/selftests/nolibc/nolibc-test.c
> +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> @@ -486,7 +486,13 @@ static int test_getpagesize(void)
>  static int test_fork(void)
>  {
>  	int status;
> -	pid_t pid = fork();
> +	pid_t pid;
> +
> +	/* flush the printf buffer to avoid child flush it */
> +	fflush(stdout);
> +	fflush(stderr);
> +
> +	pid = fork();
>  
>  	switch (pid) {
>  	case -1:
> -- 
> 2.25.1
> 
>