[PATCH v2 1/2] selftests/vm: fix inability to build any vm tests

[Axel Rasmussen]

When we stopped using KSFT_KHDR_INSTALL, a side effect is we also
changed the value of `top_srcdir`. This can be seen by looking at the
code removed by commit 49de12ba06ef
("selftests: drop KSFT_KHDR_INSTALL make target").

(Note though that this commit didn't break this, technically the one
before it did since that's the one that stopped KSFT_KHDR_INSTALL from
being used, even though the code was still there.)

Previously lib.mk reconfigured `top_srcdir` when KSFT_KHDR_INSTALL was
being used. Now, that's no longer the case.

As a result, the path to gup_test.h in vm/Makefile was wrong, and
since it's a dependency of all of the vm binaries none of them could
be built. Instead, we'd get an "error" like:

    make[1]: *** No rule to make target
        '/[...]/tools/testing/selftests/vm/compaction_test', needed by
	'all'.  Stop.

So, modify lib.mk so it once again sets top_srcdir to the root of the
kernel tree.

Fixes: f2745dc0ba3d ("selftests: stop using KSFT_KHDR_INSTALL")
Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
---
 tools/testing/selftests/lib.mk | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
index 947fc72413e9..d44c72b3abe3 100644
--- a/tools/testing/selftests/lib.mk
+++ b/tools/testing/selftests/lib.mk
@@ -40,6 +40,7 @@ ifeq (0,$(MAKELEVEL))
     endif
 endif
 selfdir = $(realpath $(dir $(filter %/lib.mk,$(MAKEFILE_LIST))))
+top_srcdir = $(selfdir)/../../..
 
 # The following are built by lib.mk common compile rules.
 # TEST_CUSTOM_PROGS should be used by tests that require
-- 
2.37.1.595.g718a3a8f04-goog