[LTP] [PATCH] mmap_24-1: Change vm.max_map_count if needed

[Martin Doucha]

If vm.max_map_count system parameter is too high, mmap24-1 may get
killed by OOM. Set the parameter to a reasonable low value so that
mmap() quickly fails as expected.

Signed-off-by: Martin Doucha <mdoucha@suse.cz>
---
 .../conformance/interfaces/mmap/24-1.c        | 35 ++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/testcases/open_posix_testsuite/conformance/interfaces/mmap/24-1.c b/testcases/open_posix_testsuite/conformance/interfaces/mmap/24-1.c
index 6cc8349e1..91677d289 100644
--- a/testcases/open_posix_testsuite/conformance/interfaces/mmap/24-1.c
+++ b/testcases/open_posix_testsuite/conformance/interfaces/mmap/24-1.c
@@ -31,12 +31,40 @@
 #include <stdint.h>
 #include "posixtest.h"
 
+#define MAX_MAP_COUNT_PATH "/proc/sys/vm/max_map_count"
+#define MAP_COUNT_LIMIT 65530
+
+void proc_write_val(const char *path, size_t val)
+{
+	FILE *procfile;
+
+	procfile = fopen(path, "r+");
+
+	if (!procfile)
+		return;
+
+	fprintf(procfile, "%zu", val);
+	fclose(procfile);
+}
+
 int main(void)
 {
 	char tmpfname[256];
 	void *pa;
-	size_t len;
+	size_t len, max_map_count = 0;
 	int fd;
+	FILE *procfile;
+
+	/* Change vm.max_map_count to avoid OOM */
+	procfile = fopen(MAX_MAP_COUNT_PATH, "r+");
+
+	if (procfile) {
+		fscanf(procfile, "%zu", &max_map_count);
+		fclose(procfile);
+	}
+
+	if (max_map_count > MAP_COUNT_LIMIT)
+		proc_write_val(MAX_MAP_COUNT_PATH, MAP_COUNT_LIMIT);
 
 	/* Size of the shared memory object */
 	size_t shm_size = 1024;
@@ -78,5 +106,10 @@ int main(void)
 
 	close(fd);
 	printf("Test FAILED: Did not get ENOMEM as expected\n");
+
+	/* Restore original vm.max_map_count */
+	if (max_map_count > MAP_COUNT_LIMIT)
+		proc_write_val(MAX_MAP_COUNT_PATH, max_map_count);
+
 	return PTS_FAIL;
 }
-- 
2.49.0