[PATCH 4.14 010/167] kselftest: fix OOM in memory compaction test

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Arnd Bergmann <arnd@xxxxxxxx>

commit 4c1baad223906943b595a887305f2e8124821dad upstream.

Running the compaction_test sometimes results in out-of-memory
failures. When I debugged this, it turned out that the code to
reset the number of hugepages to the initial value is simply
broken since we write into an open sysctl file descriptor
multiple times without seeking back to the start.

Adding the lseek here fixes the problem.

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Link: https://bugs.linaro.org/show_bug.cgi?id=3145
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 tools/testing/selftests/vm/compaction_test.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/tools/testing/selftests/vm/compaction_test.c
+++ b/tools/testing/selftests/vm/compaction_test.c
@@ -137,6 +137,8 @@ int check_compaction(unsigned long mem_f
 	printf("No of huge pages allocated = %d\n",
 	       (atoi(nr_hugepages)));
 
+	lseek(fd, 0, SEEK_SET);
+
 	if (write(fd, initial_nr_hugepages, strlen(initial_nr_hugepages))
 	    != strlen(initial_nr_hugepages)) {
 		perror("Failed to write value to /proc/sys/vm/nr_hugepages\n");