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List:       ltp-list
Subject:    [LTP] [PATCH 1/2] sched_setparam/9-1: fix hang on -rt kernel
From:       Jan Stancek <jstancek () redhat ! com>
Date:       2015-02-27 10:41:32
Message-ID: 2370af01ebeb2c4014c6d0c4252818a6138d8e19.1425033440.git.jstancek () redhat ! com
[Download RAW message or body]

As mentioned in [1], the testcase hangs on -rt kernel,
because alarm(2) will never fire. The testcase runs with
FIFO scheduling of higher priority than ksoftirqd.

This patch changes testcase in following way:
1. In good case, where child process preempts parent,
   child is able to detect this condition and terminate.
2. In bad case, where preemption fails, testcase doesn't
   rely on softirq (alarm), but hrtimer (time).
3. removes unnecessary sleep

[1] https://lkml.org/lkml/2006/1/10/481

Reported-by: Jiri Kastner <jkastner@redhat.com>
Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
 .../conformance/interfaces/sched_setparam/9-1.c    | 48 ++++++++++++++--------
 1 file changed, 32 insertions(+), 16 deletions(-)

diff --git a/testcases/open_posix_testsuite/conformance/interfaces/sched_setparam/9-1.c \
b/testcases/open_posix_testsuite/conformance/interfaces/sched_setparam/9-1.c index \
                ed90cee..354e03e 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/sched_setparam/9-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/sched_setparam/9-1.c
@@ -31,14 +31,15 @@
  *      not, the test fail.
  */
 #define _GNU_SOURCE
+#include <errno.h>
 #include <sched.h>
 #include <stdio.h>
 #include <signal.h>
+#include <stdlib.h>
 #include <sys/ipc.h>
 #include <sys/shm.h>
+#include <time.h>
 #include <unistd.h>
-#include <stdlib.h>
-#include <errno.h>
 #include "posixtest.h"
 #include "affinity.h"
 
@@ -55,6 +56,7 @@
 
 static int nb_cpu;
 static int *shmptr;
+static int mean_prio;
 
 static int get_ncpu(void)
 {
@@ -85,6 +87,7 @@ static int get_ncpu(void)
 static void child_process(void)
 {
 	struct sched_param param;
+	time_t t1, t2;
 
 	param.sched_priority = sched_get_priority_max(SCHED_FIFO);
 	if (sched_setparam(getpid(), &param) != 0) {
@@ -92,20 +95,33 @@ static void child_process(void)
 		return;
 	}
 
-	/* to avoid blocking */
-	alarm(2);
-	while (1) ;
+	t1 = time(NULL);
+	do {
+		t2 = time(NULL);
+	} while (difftime(t2, t1) <= 2);
 }
 
 static void test_process(void)
 {
-	/* to avoid blocking */
-	alarm(2);
-
-	while (1) {
-		(*shmptr)++;
+	struct sched_param param;
+	time_t t1, t2;
+
+	t1 = time(NULL);
+	do {
+		sched_getparam(getpid(), &param);
+		(*shmptr) = param.sched_priority;
+		/* if we can see that our priority has changed
+		 * that means we preempted parent, so we are done */
+		if ((*shmptr) == mean_prio)
+			break;
+
+		t2 = time(NULL);
+		/* immediately after parent forks us, we has same
+		 * priority and compete with parent for same CPU,
+		 * give parent chance to run and boost our priority */
 		sched_yield();
-	}
+	} while (difftime(t2, t1) <= 2);
+	exit(0);
 }
 
 static void kill_children(int *child_pid)
@@ -133,6 +149,8 @@ int main(void)
 		nb_cpu = 1;
 	}
 
+	mean_prio = (sched_get_priority_min(SCHED_FIFO) +
+		sched_get_priority_max(SCHED_FIFO)) / 2;
 	child_pid = malloc(nb_cpu * sizeof(int));
 
 	key = ftok("conformance/interfaces/sched_setparam/9-1.c", 1234);
@@ -194,11 +212,9 @@ int main(void)
 		return PTS_UNRESOLVED;
 	}
 
-	sleep(1);
-
-	param.sched_priority = (sched_get_priority_min(SCHED_FIFO) +
-				sched_get_priority_max(SCHED_FIFO)) / 2;
-
+	/* parent runs, which means test_process() gave up cpu,
+	 * boost its priority and check it preempted parent */
+	param.sched_priority = mean_prio;
 	oldcount = *shmptr;
 	if (sched_setparam(child_pid[i], &param) != 0) {
 		perror("An error occurs when calling sched_setparam()");
-- 
1.8.3.1


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