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

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Date:   Fri, 2 Jun 2023 12:20:34 +0200
From:   Thomas Weißschuh <thomas@...ch.de>
To:     Zhangjin Wu <falcon@...ylab.org>
Cc:     w@....eu, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] selftests/nolibc: test_fork: fix up duplicated print

On 2023-06-02 10:41:57+0800, Zhangjin Wu wrote:
> Hi, Willy
> 
> What about this one for 2023xxxx-nolibc-rv32+stkp6?
> 
> @Thomas, welcome your Reviewed-by If it is ok for you ;-)

Indeed, good catch!

Reviewed-by: Thomas Weißschuh <linux@...ssschuh.net>

> 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
> > 
> >