[LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Jan Polensky]

kill11 verifies the signal and core dump bit reported to the waiting
parent.

When /proc/sys/kernel/core_pattern starts with '|', core dumps are
handled by a userspace helper such as systemd-coredump. In such setups
the test may hang waiting for children that are blocked in the core dump
path instead of testing the wait status itself.

However, only signals with dumps_core=1 (SIGQUIT, SIGILL, SIGABRT, etc.)
actually trigger core dump handling. Signals with dumps_core=0 (SIGHUP,
SIGKILL, SIGTERM, SIGPIPE, etc.) exit immediately without touching the
core dump path.

Detect pipe-based core dumps in setup() and skip only the affected test
cases (those with dumps_core=1) in verify_kill(). This preserves test
coverage for non-core-dumping signals while preventing hangs.

Signed-off-by: Jan Polensky <japo@linux.ibm.com>
---
Link: https://lore.kernel.org/all/20260708133726.223095-1-japo@linux.ibm.com/

Changes since v1:
- Skip only core-dumping signals (dumps_core=1) instead of all test cases
- Keep core_pattern detection in setup(), move skip decision to verify_kill()
- Preserve coverage for non-core-dumping signals

 testcases/kernel/syscalls/kill/kill11.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/testcases/kernel/syscalls/kill/kill11.c b/testcases/kernel/syscalls/kill/kill11.c
index 3cf62feaed77..f9fa595a505b 100644
--- a/testcases/kernel/syscalls/kill/kill11.c
+++ b/testcases/kernel/syscalls/kill/kill11.c
@@ -25,6 +25,8 @@

 #include "tst_test.h"

+static bool pipe_based_coredump;
+
 static struct tcase {
 	int sig;
 	int dumps_core;
@@ -64,6 +66,12 @@ static void verify_kill(unsigned int n)
 	int nsig, status;
 	struct tcase *tc = &tcases[n];

+	if (tc->dumps_core && pipe_based_coredump) {
+		tst_res(TCONF, "%s: pipe-based core dump handler active",
+			tst_strsig(tc->sig));
+		return;
+	}
+
 	pid = SAFE_FORK();
 	if (!pid)
 		pause();
@@ -105,6 +113,7 @@ static void verify_kill(unsigned int n)
 static void setup(void)
 {
 	struct rlimit rlim;
+	char core_pattern[256];

 	SAFE_GETRLIMIT(RLIMIT_CORE, &rlim);

@@ -121,6 +130,14 @@ static void setup(void)
 		rlim.rlim_cur = MIN_RLIMIT_CORE;
 		SAFE_SETRLIMIT(RLIMIT_CORE, &rlim);
 	}
+
+	/*
+	 * If core_pattern pipes core dumps to a user-space helper, the child may
+	 * remain in the core dump path until the helper completes. Store the
+	 * result and skip only signals that actually request a core dump.
+	 */
+	SAFE_FILE_SCANF("/proc/sys/kernel/core_pattern", "%255s", core_pattern);
+	pipe_based_coredump = (core_pattern[0] == '|');
 }

 static struct tst_test test = {
--
2.55.0


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Re: [LTP] kill11: Skip pipe-based core dumps per signal

[linuxtestproject.agent]

Hi Jan,

On Thu, 09 Jul 2026 12:28:37 +0200, Jan Polensky wrote:
> kill11: Skip pipe-based core dumps per signal

Verdict - Reviewed

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Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Andrea Cervesato via ltp]

Reviewed-by: Andrea Cervesato <andrea.cervesato@suse.com>

--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Cyril Hrubis]

Hi!
Alternative we may change the core pattern for the duration of the test.
Does this patch fixes the issue for you?

diff --git a/testcases/kernel/syscalls/kill/kill11.c b/testcases/kernel/syscalls/kill/kill11.c
index 3cf62feae..191587368 100644
--- a/testcases/kernel/syscalls/kill/kill11.c
+++ b/testcases/kernel/syscalls/kill/kill11.c
@@ -126,7 +126,12 @@ static void setup(void)
 static struct tst_test test = {
        .needs_tmpdir = 1,
        .forks_child = 1,
+       .needs_root = 1,
        .setup = setup,
        .tcnt = ARRAY_SIZE(tcases),
        .test = verify_kill,
+       .save_restore = (const struct tst_path_val[]) {
+               {PATH_KERN_CORE_PATTERN, "core", TST_SR_TBROK},
+               {}
+       }
 };


-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Andrea Cervesato via ltp]

Hi Cyril,

> Hi!
> Alternative we may change the core pattern for the duration of the test.
> Does this patch fixes the issue for you?
> 
> diff --git a/testcases/kernel/syscalls/kill/kill11.c b/testcases/kernel/syscalls/kill/kill11.c
> index 3cf62feae..191587368 100644
> --- a/testcases/kernel/syscalls/kill/kill11.c
> +++ b/testcases/kernel/syscalls/kill/kill11.c
> @@ -126,7 +126,12 @@ static void setup(void)
>  static struct tst_test test = {
>         .needs_tmpdir = 1,
>         .forks_child = 1,
> +       .needs_root = 1,

I don't know if it's a good idea to switch to privileged user, since
we would remove the test from parallel execution.

Regards,
--
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Cyril Hrubis]

Hi!
> > Alternative we may change the core pattern for the duration of the test.
> > Does this patch fixes the issue for you?
> > 
> > diff --git a/testcases/kernel/syscalls/kill/kill11.c b/testcases/kernel/syscalls/kill/kill11.c
> > index 3cf62feae..191587368 100644
> > --- a/testcases/kernel/syscalls/kill/kill11.c
> > +++ b/testcases/kernel/syscalls/kill/kill11.c
> > @@ -126,7 +126,12 @@ static void setup(void)
> >  static struct tst_test test = {
> >         .needs_tmpdir = 1,
> >         .forks_child = 1,
> > +       .needs_root = 1,
> 
> I don't know if it's a good idea to switch to privileged user, since
> we would remove the test from parallel execution.

Well either we do that, or we skip the signals that dump core when we
are dumping into the pipe.

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Andrea Cervesato via ltp]

> Well either we do that, or we skip the signals that dump core when we
> are dumping into the pipe.

To me it looks good to skip the signals which are not allowing child
to be killed after coredump. It's a systemd feature we can't workaround
in this case.

--
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SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Cyril Hrubis]

Hi!
> > Well either we do that, or we skip the signals that dump core when we
> > are dumping into the pipe.
> 
> To me it looks good to skip the signals which are not allowing child
> to be killed after coredump. It's a systemd feature we can't workaround
> in this case.

Thinking of it once more, I wonder what exactly fails in the
systemd-coredump case. I guess that it may delay the test execution a
bit but the crashed process should eventualy quit and the test wait()
call should collect it. If that wasn't the case systemd-coredump would
break one of the fundamentals of UNIX process management.

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Andrea Cervesato via ltp]

> Hi!
> > > Well either we do that, or we skip the signals that dump core when we
> > > are dumping into the pipe.
> > 
> > To me it looks good to skip the signals which are not allowing child
> > to be killed after coredump. It's a systemd feature we can't workaround
> > in this case.
> 
> Thinking of it once more, I wonder what exactly fails in the
> systemd-coredump case. I guess that it may delay the test execution a
> bit but the crashed process should eventualy quit and the test wait()
> call should collect it. If that wasn't the case systemd-coredump would
> break one of the fundamentals of UNIX process management.

Let's forget about systemd for a second.

The problem is that by using `pause()` that is not draining the buffer we
never ends the piped user-space helper. The default behaviour for a piped
helper is that kernel collect the coredump until helper drains the pipe.

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SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Cyril Hrubis]

Hi!
> > Thinking of it once more, I wonder what exactly fails in the
> > systemd-coredump case. I guess that it may delay the test execution a
> > bit but the crashed process should eventualy quit and the test wait()
> > call should collect it. If that wasn't the case systemd-coredump would
> > break one of the fundamentals of UNIX process management.
> 
> Let's forget about systemd for a second.
> 
> The problem is that by using `pause()` that is not draining the buffer we
> never ends the piped user-space helper. The default behaviour for a piped
> helper is that kernel collect the coredump until helper drains the pipe.

Which would mean that the system this is failing on is mis-configured at
best. I've tested this on Leap 16.0 that uses systemd-coredump and
everything works fine there.

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chrubis@suse.cz

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Re: [LTP] [PATCH v2 1/1] kill11: Skip pipe-based core dumps per signal

[Jan Polensky]

On Fri, Jul 10, 2026 at 02:27:11PM +0200, Cyril Hrubis wrote:
> Hi!
> Alternative we may change the core pattern for the duration of the test.
> Does this patch fixes the issue for you?
>
> diff --git a/testcases/kernel/syscalls/kill/kill11.c b/testcases/kernel/syscalls/kill/kill11.c
> index 3cf62feae..191587368 100644
> --- a/testcases/kernel/syscalls/kill/kill11.c
> +++ b/testcases/kernel/syscalls/kill/kill11.c
> @@ -126,7 +126,12 @@ static void setup(void)
>  static struct tst_test test = {
>         .needs_tmpdir = 1,
>         .forks_child = 1,
> +       .needs_root = 1,
>         .setup = setup,
>         .tcnt = ARRAY_SIZE(tcases),
>         .test = verify_kill,
> +       .save_restore = (const struct tst_path_val[]) {
> +               {PATH_KERN_CORE_PATTERN, "core", TST_SR_TBROK},
> +               {}
> +       }
>  };
>
>
> --
> Cyril Hrubis
> chrubis@suse.cz
Hi Cyril,

yes, this patch fixes the issue completely for me.

I tested it on both x86_64 and s390 with different configurations and could no longer reproduce the failures.

Using a non-pipe core_pattern during the test is a good solution for my setup.

Regards,
Jan

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