Re: [LTP] [PATCH] unshare03: using soft limit of NOFILE

[Petr Vorel <pvorel@suse.cz>]

Hi lufei, Al,

> Hi Petr,

> Yes, kselftest tools/testing/selftests/core/unshare_test.c failed as
> well, dup2 failed:

> ```
> unshare_test.c:60:unshare_EMFILE:Expected dup2(2, nr_open + 64) (-1) >= 0 (0)
> ```

Thanks for info.  Maybe also sending a patch to kselftest?

Kind regards,
Petr

PS: lufei, please keep Cc to keep other informed.

> Thanks for reply.
> Best regards.

> On Thu, Mar 27, 2025 at 11:33:36AM +0100, Petr Vorel wrote:
> > Hi lufei, Al,

> > @Al, you're the author of the original test unshare_test.c [1] in kselftest.
> > This is a patch to LTP test unshare03.c, which is based on your test.

> > > I think it's safer to set NOFILE increasing from soft limit than from
> > > hard limit.

> > > Hard limit may lead to dup2 ENOMEM error which bring the result to
> > > TBROK on little memory machine. (e.g. 2GB memory in my situation, hard
> > > limit in /proc/sys/fs/nr_open come out to be 1073741816)

> > IMHO lowering number to ~ half (in my case) by using rlimit.rlim_max instead of
> > /proc/sys/fs/nr_open should not affect the functionality of the test, right?
> > Or am I missing something obvious?

> > @lufei I guess kselftest tools/testing/selftests/core/unshare_test.c would fail
> > for you as well, right?

> > Kind regards,
> > Petr

> > [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=611fbeb44a777e5ab54ab3127ec85f72147911d8

> > > Signed-off-by: lufei <lufei@uniontech.com>
> > > ---
> > >  testcases/kernel/syscalls/unshare/unshare03.c | 14 ++++++--------
> > >  1 file changed, 6 insertions(+), 8 deletions(-)

> > > diff --git a/testcases/kernel/syscalls/unshare/unshare03.c b/testcases/kernel/syscalls/unshare/unshare03.c
> > > index 7c5e71c4e..bb568264c 100644
> > > --- a/testcases/kernel/syscalls/unshare/unshare03.c
> > > +++ b/testcases/kernel/syscalls/unshare/unshare03.c
> > > @@ -24,7 +24,7 @@

> > >  static void run(void)
> > >  {
> > > -	int nr_open;
> > > +	int rlim_max;
> > >  	int nr_limit;
> > >  	struct rlimit rlimit;
> > >  	struct tst_clone_args args = {
> > > @@ -32,14 +32,12 @@ static void run(void)
> > >  		.exit_signal = SIGCHLD,
> > >  	};

> > > -	SAFE_FILE_SCANF(FS_NR_OPEN, "%d", &nr_open);
> > > -	tst_res(TDEBUG, "Maximum number of file descriptors: %d", nr_open);
> > > +	SAFE_GETRLIMIT(RLIMIT_NOFILE, &rlimit);
> > > +	rlim_max = rlimit.rlim_max;

> > > -	nr_limit = nr_open + NR_OPEN_LIMIT;
> > > +	nr_limit = rlim_max + NR_OPEN_LIMIT;
> > >  	SAFE_FILE_PRINTF(FS_NR_OPEN, "%d", nr_limit);

> > > -	SAFE_GETRLIMIT(RLIMIT_NOFILE, &rlimit);
> > > -
> > >  	rlimit.rlim_cur = nr_limit;
> > >  	rlimit.rlim_max = nr_limit;

> > > @@ -47,10 +45,10 @@ static void run(void)
> > >  	tst_res(TDEBUG, "Set new maximum number of file descriptors to : %d",
> > >  		nr_limit);

> > > -	SAFE_DUP2(2, nr_open + NR_OPEN_DUP);
> > > +	SAFE_DUP2(2, rlim_max + NR_OPEN_DUP);

> > >  	if (!SAFE_CLONE(&args)) {
> > > -		SAFE_FILE_PRINTF(FS_NR_OPEN, "%d", nr_open);
> > > +		SAFE_FILE_PRINTF(FS_NR_OPEN, "%d", rlim_max);
> > >  		TST_EXP_FAIL(unshare(CLONE_FILES), EMFILE);
> > >  		exit(0);
> > >  	}


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