[LTP] [PATCH v1] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[LTP] [PATCH v1] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[Stephen Bertram via ltp]

The post-close wait used a fixed 1000000 us cap on exponential backoff
(~524 ms total). Scale that cap with tst_multiply_timeout() so debug
kernels and LTP_TIMEOUT_MUL apply, fixing failures under parallel
Kirk workers without changing default behavior on non-debug systems.

Before (only with case 100):

pipe13.c:50: TINFO: Creating 100 child processes
pipe13.c:81: TINFO: pid 435007 still sleeps
...
pipe13.c:81: TINFO: pid 435300 still sleeps
pipe13.c:89: TFAIL: Closed pipe didn't wake up everyone
The list varied but sometimes up to 20 would remained asleep.

After using tst_multiply_timeout(), test passes.

The failure before would happen, when using 4 paralell workers
on a debug kernel, about 1 to 2 times when iterated 5 times.
With the addition of the function, under the same conditions,
it has not failed in 100 iterations.

Signed-off-by: Stephen Bertram <sbertram@redhat.com>
---
 testcases/kernel/syscalls/pipe/pipe13.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/testcases/kernel/syscalls/pipe/pipe13.c b/testcases/kernel/syscalls/pipe/pipe13.c
index 5d76e1f00..cf1ccbcbc 100644
--- a/testcases/kernel/syscalls/pipe/pipe13.c
+++ b/testcases/kernel/syscalls/pipe/pipe13.c
@@ -44,6 +44,7 @@ static void verify_pipe(unsigned int n)
 	int ret;
 	unsigned int i, cnt = 0, sleep_us = 1, fail = 0;
 	unsigned int child_num = tcases[n];
+	unsigned int sleep_us_cap = tst_multiply_timeout(1000) * 1000U;
 	int pid[child_num];
 
 	SAFE_PIPE(fds);
@@ -60,7 +61,7 @@ static void verify_pipe(unsigned int n)
 	SAFE_CLOSE(fds[0]);
 	SAFE_CLOSE(fds[1]);
 
-	while (cnt < child_num && sleep_us < 1000000) {
+	while (cnt < child_num && sleep_us < sleep_us_cap) {
 		ret = waitpid(-1, NULL, WNOHANG);
 		if (ret < 0)
 			tst_brk(TBROK | TERRNO, "waitpid()");
-- 
2.54.0


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Re: [LTP] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[linuxtestproject.agent]

Hi Stephen,

On Fri, 10 Jul 2026 10:31:19 -0400, Stephen Bertram wrote:
> pipe13: Scale child reap window with LTP_TIMEOUT_MUL

> The post-close wait used a fixed 1000000 us cap on exponential backoff
> (~524 ms total).

The total accumulated sleep time is 1+2+4+...+524288 = 1048575 us,
which is approximately 1048 ms (~1 second), not 524 ms.

524288 us (~524 ms) is the maximum value of a single usleep() call
within the loop -- not the total.

> on a debug kernel, about 1 to 2 times when iterated 5 times.
> With the addition of the function, under the same conditions,
> it has not failed in 100 iterations.

"paralell" -> "parallel".

Verdict - Needs revision

Pre-existing: pipe13.c carries an old-style "Test Description:" comment
block instead of the /*\ ... */ RST doc-comment format now required by
LTP conventions. Not introduced by this patch, but worth fixing in a
follow-up.

---
Note:

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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 v1] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[Andrea Cervesato via ltp]

Hi Stephen,

> The post-close wait used a fixed 1000000 us cap on exponential backoff
> (~524 ms total). Scale that cap with tst_multiply_timeout() so debug
> kernels and LTP_TIMEOUT_MUL apply, fixing failures under parallel
> Kirk workers without changing default behavior on non-debug systems.
> 
> Before (only with case 100):
> 
> pipe13.c:50: TINFO: Creating 100 child processes
> pipe13.c:81: TINFO: pid 435007 still sleeps
> ...
> pipe13.c:81: TINFO: pid 435300 still sleeps
> pipe13.c:89: TFAIL: Closed pipe didn't wake up everyone
> The list varied but sometimes up to 20 would remained asleep.
> 
> After using tst_multiply_timeout(), test passes.
> 
> The failure before would happen, when using 4 paralell workers
> on a debug kernel, about 1 to 2 times when iterated 5 times.
> With the addition of the function, under the same conditions,
> it has not failed in 100 iterations.
> 
> Signed-off-by: Stephen Bertram <sbertram@redhat.com>
> ---
>  testcases/kernel/syscalls/pipe/pipe13.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/testcases/kernel/syscalls/pipe/pipe13.c b/testcases/kernel/syscalls/pipe/pipe13.c
> index 5d76e1f00..cf1ccbcbc 100644
> --- a/testcases/kernel/syscalls/pipe/pipe13.c
> +++ b/testcases/kernel/syscalls/pipe/pipe13.c
> @@ -44,6 +44,7 @@ static void verify_pipe(unsigned int n)
>  	int ret;
>  	unsigned int i, cnt = 0, sleep_us = 1, fail = 0;
>  	unsigned int child_num = tcases[n];
> +	unsigned int sleep_us_cap = tst_multiply_timeout(1000) * 1000U;

Even better: we can create a function to reap children and verify
if they are completed while counting them.
Then we can use TST_RETRY_FN_EXP_BACKOFF() on it.

The problem is that we are waiting a fixed amount of time (~1s) that
is not enough when system is overloaded.

Most likely, when you are calling kirk parallel execution, other tests
are overloading the system and this test fails accordingly.

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

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Re: [LTP] [PATCH v1] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[Stephen Bertram via ltp]

Hi Andrea,

When isolated, I can reproduce the issue, always with the 100 scenario, on
a debug kernel. The debug kernel I use has locking and kmemleak active
which slows performance greatly.

As for the scaling, LTP_TIMEOUT_MUL will allow users to scale larger as
needed, so I don't think the initial time, 1s, is an issue with the
implementation. It keeps it as before, without using the multiple, but now
allows us to incorporate the multiple for longer wait times if needed. If
you think we should start higher I could, but when I run this test without
even using the variable multiplier, it works fine because
tst_multiply_timeout also adds a 4x multiple for debug kernels.

Thank you for the suggestion and I will make changes to work
with TST_RETRY_FN_EXP_BACKOFF().

thanks,

stephen
He/His/Him


On Mon, Jul 13, 2026 at 5:11 AM Andrea Cervesato <andrea.cervesato@suse.com>
wrote:

> Hi Stephen,
>
> > The post-close wait used a fixed 1000000 us cap on exponential backoff
> > (~524 ms total). Scale that cap with tst_multiply_timeout() so debug
> > kernels and LTP_TIMEOUT_MUL apply, fixing failures under parallel
> > Kirk workers without changing default behavior on non-debug systems.
> >
> > Before (only with case 100):
> >
> > pipe13.c:50: TINFO: Creating 100 child processes
> > pipe13.c:81: TINFO: pid 435007 still sleeps
> > ...
> > pipe13.c:81: TINFO: pid 435300 still sleeps
> > pipe13.c:89: TFAIL: Closed pipe didn't wake up everyone
> > The list varied but sometimes up to 20 would remained asleep.
> >
> > After using tst_multiply_timeout(), test passes.
> >
> > The failure before would happen, when using 4 paralell workers
> > on a debug kernel, about 1 to 2 times when iterated 5 times.
> > With the addition of the function, under the same conditions,
> > it has not failed in 100 iterations.
> >
> > Signed-off-by: Stephen Bertram <sbertram@redhat.com>
> > ---
> >  testcases/kernel/syscalls/pipe/pipe13.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/testcases/kernel/syscalls/pipe/pipe13.c
> b/testcases/kernel/syscalls/pipe/pipe13.c
> > index 5d76e1f00..cf1ccbcbc 100644
> > --- a/testcases/kernel/syscalls/pipe/pipe13.c
> > +++ b/testcases/kernel/syscalls/pipe/pipe13.c
> > @@ -44,6 +44,7 @@ static void verify_pipe(unsigned int n)
> >       int ret;
> >       unsigned int i, cnt = 0, sleep_us = 1, fail = 0;
> >       unsigned int child_num = tcases[n];
> > +     unsigned int sleep_us_cap = tst_multiply_timeout(1000) * 1000U;
>
> Even better: we can create a function to reap children and verify
> if they are completed while counting them.
> Then we can use TST_RETRY_FN_EXP_BACKOFF() on it.
>
> The problem is that we are waiting a fixed amount of time (~1s) that
> is not enough when system is overloaded.
>
> Most likely, when you are calling kirk parallel execution, other tests
> are overloading the system and this test fails accordingly.
>
> Regards,
> --
> Andrea Cervesato
> SUSE QE Automation Engineer Linux
> andrea.cervesato@suse.com
>
>

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[LTP] [PATCH v2] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[Stephen Bertram via ltp]

The post-close wait used a fixed 1000000 us cap on exponential backoff.
Scale that cap with tst_multiply_timeout() so debug
kernels and LTP_TIMEOUT_MUL apply, fixing failures under parallel
Kirk workers without changing default behavior on non-debug systems.

Before (only with case 100):

pipe13.c:50: TINFO: Creating 100 child processes
pipe13.c:81: TINFO: pid 435007 still sleeps
...
pipe13.c:81: TINFO: pid 435300 still sleeps
pipe13.c:89: TFAIL: Closed pipe didn't wake up everyone
The list varied but sometimes up to 20 would remained asleep.

Test is passing after using TST_RETRY_FN_EXP_BACKOFF() so timeout
scaling follows the standard LTP path (tst_multiply_timeout, debug
kconfig, LTP_TIMEOUT_MUL).

The failure before would happen, when using 4 paralell workers
on a debug kernel, about 1 to 2 times when iterated 5 times.
Tested on aarch64 debug+PREEMPT_RT: kirk -w 4 pipe13 -i 100, 400 runs,
0 fail.

Signed-off-by: Stephen Bertram <sbertram@redhat.com>
---
 testcases/kernel/syscalls/pipe/pipe13.c | 44 +++++++++++++++----------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/testcases/kernel/syscalls/pipe/pipe13.c b/testcases/kernel/syscalls/pipe/pipe13.c
index 5d76e1f00..7f7685a2c 100644
--- a/testcases/kernel/syscalls/pipe/pipe13.c
+++ b/testcases/kernel/syscalls/pipe/pipe13.c
@@ -26,6 +26,28 @@ static unsigned int tcases[] = {
 };
 
 static int fds[2];
+static unsigned int reap_child_num;
+static unsigned int reap_count;
+static int *reap_pids;
+
+static int reap_children_once(void)
+{
+	unsigned int i;
+	int ret;
+
+	while ((ret = waitpid(-1, NULL, WNOHANG)) > 0) {
+		reap_count++;
+		for (i = 0; i < reap_child_num; i++) {
+			if (reap_pids[i] == ret)
+				reap_pids[i] = 0;
+		}
+	}
+	if (ret < 0 && errno != ECHILD)
+		tst_brk(TBROK | TERRNO, "waitpid()");
+	return reap_count;
+}
+
+#define ALL_CHILDREN_REAPED(cnt) ((unsigned int)(cnt) >= reap_child_num)
 
 static void do_child(unsigned int i)
 {
@@ -41,8 +63,7 @@ static void do_child(unsigned int i)
 
 static void verify_pipe(unsigned int n)
 {
-	int ret;
-	unsigned int i, cnt = 0, sleep_us = 1, fail = 0;
+	unsigned int i, fail = 0;
 	unsigned int child_num = tcases[n];
 	int pid[child_num];
 
@@ -60,21 +81,10 @@ static void verify_pipe(unsigned int n)
 	SAFE_CLOSE(fds[0]);
 	SAFE_CLOSE(fds[1]);
 
-	while (cnt < child_num && sleep_us < 1000000) {
-		ret = waitpid(-1, NULL, WNOHANG);
-		if (ret < 0)
-			tst_brk(TBROK | TERRNO, "waitpid()");
-		if (ret > 0) {
-			cnt++;
-			for (i = 0; i < child_num; i++) {
-				if (pid[i] == ret)
-					pid[i] = 0;
-			}
-			continue;
-		}
-		usleep(sleep_us);
-		sleep_us *= 2;
-	}
+	reap_child_num = child_num;
+	reap_count = 0;
+	reap_pids = pid;
+	TST_RETRY_FN_EXP_BACKOFF(reap_children_once(), ALL_CHILDREN_REAPED, 1);
 
 	for (i = 0; i < child_num; i++) {
 		if (pid[i]) {
-- 
2.54.0


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Re: [LTP] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[linuxtestproject.agent]

Hi Stephen,

On Mon, 13 Jul 2026 12:07:20 -0400, Stephen Bertram wrote:
> pipe13: Scale child reap window with LTP_TIMEOUT_MUL

> The failure before would happen, when using 4 paralell workers

Typo: "paralell" should be "parallel".

Verdict - Needs revision

---
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,
LTP AI Reviewer

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

[LTP] [PATCH v3] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[Stephen Bertram via ltp]

The post-close wait used a fixed 1000000 us cap on exponential backoff.
Scale that cap with tst_multiply_timeout() so debug
kernels and LTP_TIMEOUT_MUL apply, fixing failures under parallel
Kirk workers without changing default behavior on non-debug systems.

Before (only with case 100):

pipe13.c:50: TINFO: Creating 100 child processes
pipe13.c:81: TINFO: pid 435007 still sleeps
...
pipe13.c:81: TINFO: pid 435300 still sleeps
pipe13.c:89: TFAIL: Closed pipe didn't wake up everyone
The list varied but sometimes up to 20 would remained asleep.

Test is passing after using TST_RETRY_FN_EXP_BACKOFF() so timeout
scaling follows the standard LTP path (tst_multiply_timeout, debug
kconfig, LTP_TIMEOUT_MUL).

The failure before would happen, when using 4 parallel workers
on a debug kernel, about 1 to 2 times when iterated 5 times.
Tested on aarch64 debug+PREEMPT_RT: kirk -w 4 pipe13 -i 100, 400 runs,
0 fail.

Signed-off-by: Stephen Bertram <sbertram@redhat.com>
---
 testcases/kernel/syscalls/pipe/pipe13.c | 44 +++++++++++++++----------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/testcases/kernel/syscalls/pipe/pipe13.c b/testcases/kernel/syscalls/pipe/pipe13.c
index 5d76e1f00..7f7685a2c 100644
--- a/testcases/kernel/syscalls/pipe/pipe13.c
+++ b/testcases/kernel/syscalls/pipe/pipe13.c
@@ -26,6 +26,28 @@ static unsigned int tcases[] = {
 };
 
 static int fds[2];
+static unsigned int reap_child_num;
+static unsigned int reap_count;
+static int *reap_pids;
+
+static int reap_children_once(void)
+{
+	unsigned int i;
+	int ret;
+
+	while ((ret = waitpid(-1, NULL, WNOHANG)) > 0) {
+		reap_count++;
+		for (i = 0; i < reap_child_num; i++) {
+			if (reap_pids[i] == ret)
+				reap_pids[i] = 0;
+		}
+	}
+	if (ret < 0 && errno != ECHILD)
+		tst_brk(TBROK | TERRNO, "waitpid()");
+	return reap_count;
+}
+
+#define ALL_CHILDREN_REAPED(cnt) ((unsigned int)(cnt) >= reap_child_num)
 
 static void do_child(unsigned int i)
 {
@@ -41,8 +63,7 @@ static void do_child(unsigned int i)
 
 static void verify_pipe(unsigned int n)
 {
-	int ret;
-	unsigned int i, cnt = 0, sleep_us = 1, fail = 0;
+	unsigned int i, fail = 0;
 	unsigned int child_num = tcases[n];
 	int pid[child_num];
 
@@ -60,21 +81,10 @@ static void verify_pipe(unsigned int n)
 	SAFE_CLOSE(fds[0]);
 	SAFE_CLOSE(fds[1]);
 
-	while (cnt < child_num && sleep_us < 1000000) {
-		ret = waitpid(-1, NULL, WNOHANG);
-		if (ret < 0)
-			tst_brk(TBROK | TERRNO, "waitpid()");
-		if (ret > 0) {
-			cnt++;
-			for (i = 0; i < child_num; i++) {
-				if (pid[i] == ret)
-					pid[i] = 0;
-			}
-			continue;
-		}
-		usleep(sleep_us);
-		sleep_us *= 2;
-	}
+	reap_child_num = child_num;
+	reap_count = 0;
+	reap_pids = pid;
+	TST_RETRY_FN_EXP_BACKOFF(reap_children_once(), ALL_CHILDREN_REAPED, 1);
 
 	for (i = 0; i < child_num; i++) {
 		if (pid[i]) {
-- 
2.54.0


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Re: [LTP] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[linuxtestproject.agent]

Hi Stephen,

On Mon, Jul 13 2026 13:01:28 -0400, Stephen Bertram wrote:
> pipe13: Scale child reap window with LTP_TIMEOUT_MUL

Verdict - Reviewed

---
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,
LTP AI Reviewer

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Re: [LTP] [PATCH v3] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[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 v3] pipe13: Scale child reap window with LTP_TIMEOUT_MUL

[Andrea Cervesato via ltp]

Merged, Thanks!

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

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