Re: [PATCH] perf test: Handle fd gaps in test__dso_data_reopen

[Michael Petlan <mpetlan@redhat.com>]

On Wed, 30 Jun 2021, Michael Petlan wrote:
> On Fri, 25 Jun 2021, Eirik Fuller wrote:
> > https://github.com/beaker-project/restraint/issues/215 describes a file
> > descriptor leak which revealed the test failure described here.
> > 
> > The 'DSO data reopen' perf test assumes that RLIMIT_NOFILE limits the
> > number of open file descriptors, but it actually limits newly opened
> > file descriptors. When the file descriptor limit is reduced, file
> > descriptors already open remain open regardless of the new limit. This
> > test failure does not occur if open file descriptors are contiguous,
> > beginning at zero.
> > 
> > The following command triggers this perf test failure.
> > 
> > perf test 'DSO data reopen' 3>/dev/null 8>/dev/null
> > 
> > This patch determines the file descriptor limit by opening four files
> > and then closing them. The limit is set to the fourth file descriptor,
> > leaving only the first three available because any newly opened file
> > descriptor must be less than the limit.
> > 
> > Signed-off-by: Eirik Fuller <efuller@redhat.com>
> 
> Acked-by: Michael Petlan <mpetlan@redhat.com>

Hi Arnaldo,
kindly reminder, could this get merged?

Thank you.

> 
> > ---
> >  tools/perf/tests/dso-data.c | 14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/tests/dso-data.c b/tools/perf/tests/dso-data.c
> > index 627c1aaf1c9e..43e1b01e5afc 100644
> > --- a/tools/perf/tests/dso-data.c
> > +++ b/tools/perf/tests/dso-data.c
> > @@ -308,10 +308,20 @@ int test__dso_data_cache(struct test *test __maybe_unused, int subtest __maybe_u
> >  	return 0;
> >  }
> >  
> > +static long new_limit(int count)
> > +{
> > +	int fd = open("/dev/null", O_RDONLY);
> > +	long ret = fd;
> > +	if (count > 0)
> > +		ret = new_limit(--count);
> > +	close(fd);
> > +	return ret;
> > +}
> > +
> >  int test__dso_data_reopen(struct test *test __maybe_unused, int subtest __maybe_unused)
> >  {
> >  	struct machine machine;
> > -	long nr_end, nr = open_files_cnt();
> > +	long nr_end, nr = open_files_cnt(), lim = new_limit(3);
> >  	int fd, fd_extra;
> >  
> >  #define dso_0 (dsos[0])
> > @@ -334,7 +344,7 @@ int test__dso_data_reopen(struct test *test __maybe_unused, int subtest __maybe_
> >  
> >  	/* Make sure we are able to open 3 fds anyway */
> >  	TEST_ASSERT_VAL("failed to set file limit",
> > -			!set_fd_limit((nr + 3)));
> > +			!set_fd_limit((lim)));
> >  
> >  	TEST_ASSERT_VAL("failed to create dsos\n", !dsos__create(3, TEST_FILE_SIZE));
> >  
> > -- 
> > 2.27.0
> > 
> > 
> 
>