[PATCH mm-unstable] selftests/vm: fix "add thp collapse file and tmpfs testing" for tmpfs

["Zach O'Keefe" <zokeefe@google.com>]

In write_settings() and save_settings() we properly only read/write
/sys/block/<device>/queue/read_ahead_kb if the test file is not backed
by tmpfs.  However, in get_finfo(), we unconditionally attempt to
resolve the major/minor device pair and search for device interface,
which we fail to do when the device is the null device (major 0), as is
the case when stat(2)'ing a tmpfs-backed file.

Only resolve path to queue/read_ahead_kb when dealing with non-tmpfs
files.

Fixes: 64b9fb1fa904 ("selftests/vm: add thp collapse file and tmpfs testing")
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
---
 tools/testing/selftests/vm/khugepaged.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/vm/khugepaged.c b/tools/testing/selftests/vm/khugepaged.c
index 702f64b3aa08..ad46fdb57d78 100644
--- a/tools/testing/selftests/vm/khugepaged.c
+++ b/tools/testing/selftests/vm/khugepaged.c
@@ -453,6 +453,8 @@ static void get_finfo(const char *dir)
 		exit(EXIT_FAILURE);
 	}
 	finfo.type = fs.f_type == TMPFS_MAGIC ? VMA_SHMEM : VMA_FILE;
+	if (finfo.type == VMA_SHMEM)
+		return;
 
 	/* Find owning device's queue/read_ahead_kb control */
 	if (snprintf(path, sizeof(path), "/sys/dev/block/%d:%d/uevent",
-- 
2.37.2.789.g6183377224-goog