selftests/powerpc: Test the THP bug we fixed in the previous commit

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

3 files changed, 91 insertions, 1 deletions

diff --git a/tools/testing/selftests/powerpc/Makefile b/tools/testing/selftests/powerpc/Makefile
index 316194f26ff4..b3dbe9ef1a40 100644
--- a/tools/testing/selftests/powerpc/Makefile
+++ b/tools/testing/selftests/powerpc/Makefile
@@ -13,7 +13,7 @@ CFLAGS := -Wall -O2 -flto -Wall -Werror -DGIT_VERSION='"$(GIT_VERSION)"' -I$(CUR
 
 export CC CFLAGS
 
-TARGETS = pmu copyloops
+TARGETS = pmu copyloops mm
 
 endif
 
diff --git a/tools/testing/selftests/powerpc/mm/Makefile b/tools/testing/selftests/powerpc/mm/Makefile
new file mode 100644
index 000000000000..357ccbd6bad9
--- /dev/null
+++ b/tools/testing/selftests/powerpc/mm/Makefile
@@ -0,0 +1,18 @@
+noarg:
+        $(MAKE) -C ../
+
+PROGS := hugetlb_vs_thp_test
+
+all: $(PROGS)
+
+$(PROGS): ../harness.c
+
+run_tests: all
+        @-for PROG in $(PROGS); do \
+                ./$$PROG; \
+        done;
+
+clean:
+        rm -f $(PROGS)
+
+.PHONY: all run_tests clean
diff --git a/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c b/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c
new file mode 100644
index 000000000000..3d8e5b033e1d
--- /dev/null
+++ b/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c
@@ -0,0 +1,72 @@
+#include <stdio.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "utils.h"
+
+/* This must match the huge page & THP size */
+#define SIZE    (16 * 1024 * 1024)
+
+static int test_body(void)
+{
+        void *addr;
+        char *p;
+
+        addr = (void *)0xa0000000;
+
+        p = mmap(addr, SIZE, PROT_READ | PROT_WRITE,
+                 MAP_HUGETLB | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+        if (p != MAP_FAILED) {
+                /*
+                 * Typically the mmap will fail because no huge pages are
+                 * allocated on the system. But if there are huge pages
+                 * allocated the mmap will succeed. That's fine too, we just
+                 * munmap here before continuing.
+                 */
+                munmap(addr, SIZE);
+        }
+
+        p = mmap(addr, SIZE, PROT_READ | PROT_WRITE,
+                 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+        if (p == MAP_FAILED) {
+                printf("Mapping failed @ %p\n", addr);
+                perror("mmap");
+                return 1;
+        }
+
+        /*
+         * Either a user or kernel access is sufficient to trigger the bug.
+         * A kernel access is easier to spot & debug, as it will trigger the
+         * softlockup or RCU stall detectors, and when the system is kicked
+         * into xmon we get a backtrace in the kernel.
+         *
+         * A good option is:
+         *  getcwd(p, SIZE);
+         *
+         * For the purposes of this testcase it's preferable to spin in
+         * userspace, so the harness can kill us if we get stuck. That way we
+         * see a test failure rather than a dead system.
+         */
+        *p = 0xf;
+
+        munmap(addr, SIZE);
+
+        return 0;
+}
+
+static int test_main(void)
+{
+        int i;
+
+        /* 10,000 because it's a "bunch", and completes reasonably quickly */
+        for (i = 0; i < 10000; i++)
+                if (test_body())
+                        return 1;
+
+        return 0;
+}
+
+int main(void)
+{
+        return test_harness(test_main, "hugetlb_vs_thp");
+}