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From:   Breno Leitao <leitao@debian.org>
To:     mike.kravetz@oracle.com, muchun.song@linux.dev,
        akpm@linux-foundation.org, Shuah Khan <shuah@kernel.org>
Cc:     linux-mm@kvack.org, riel@surriel.com,
        linux-kernel@vger.kernel.org (open list),
        linux-kselftest@vger.kernel.org (open list:KERNEL SELFTEST FRAMEWORK)
Subject: [PATCH v2 2/2] selftests/mm: Add a new test for madv and hugetlb
Date:   Thu,  5 Oct 2023 09:39:22 -0700
Message-Id: <20231005163922.87568-3-leitao@debian.org>
In-Reply-To: <20231005163922.87568-1-leitao@debian.org>
References: <20231005163922.87568-1-leitao@debian.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Create a selftest that exercises the race between page faults and
madvise(MADV_DONTNEED) in the same huge page. Do it by running two
threads that touches the huge page and madvise(MADV_DONTNEED) at the same
time.

In case of a SIGBUS coming at pagefault, the test should fail, since we
hit the bug.

The test doesn't have a signal handler, and if it fails, it fails like
the following

  ----------------------------------
  running ./hugetlb_fault_after_madv
  ----------------------------------
  ./run_vmtests.sh: line 186: 595563 Bus error    (core dumped) "$@"
  [FAIL]

This selftest goes together with the fix of the bug[1] itself.

[1] https://lore.kernel.org/all/20231001005659.2185316-1-riel@surriel.com/#r

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 tools/testing/selftests/mm/Makefile           |  1 +
 .../selftests/mm/hugetlb_fault_after_madv.c   | 73 +++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh     |  4 +
 3 files changed, 78 insertions(+)
 create mode 100644 tools/testing/selftests/mm/hugetlb_fault_after_madv.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 6a9fc5693145..e71ec9910c62 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -68,6 +68,7 @@ TEST_GEN_FILES += split_huge_page_test
 TEST_GEN_FILES += ksm_tests
 TEST_GEN_FILES += ksm_functional_tests
 TEST_GEN_FILES += mdwe_test
+TEST_GEN_FILES += hugetlb_fault_after_madv
 
 ifneq ($(ARCH),arm64)
 TEST_GEN_PROGS += soft-dirty
diff --git a/tools/testing/selftests/mm/hugetlb_fault_after_madv.c b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
new file mode 100644
index 000000000000..73b81c632366
--- /dev/null
+++ b/tools/testing/selftests/mm/hugetlb_fault_after_madv.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "vm_util.h"
+#include "../kselftest.h"
+
+#define MMAP_SIZE (1 << 21)
+#define INLOOP_ITER 100
+
+char *huge_ptr;
+
+/* Touch the memory while it is being madvised() */
+void *touch(void *unused)
+{
+	char *ptr = (char *)huge_ptr;
+
+	for (int i = 0; i < INLOOP_ITER; i++)
+		ptr[0] = '.';
+
+	return NULL;
+}
+
+void *madv(void *unused)
+{
+	usleep(rand() % 10);
+
+	for (int i = 0; i < INLOOP_ITER; i++)
+		madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
+
+	return NULL;
+}
+
+int main(void)
+{
+	unsigned long free_hugepages;
+	pthread_t thread1, thread2;
+	/*
+	 * On kernel 6.4, we are able to reproduce the problem with ~1000
+	 * interactions
+	 */
+	int max = 10000;
+
+	srand(getpid());
+
+	free_hugepages = get_free_hugepages();
+	if (free_hugepages != 1) {
+		ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
+			       free_hugepages);
+	}
+
+	while (max--) {
+		huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
+				MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
+				-1, 0);
+
+		if ((unsigned long)huge_ptr == -1)
+			ksft_exit_skip("Failed to allocated huge page\n");
+
+		pthread_create(&thread1, NULL, madv, NULL);
+		pthread_create(&thread2, NULL, touch, NULL);
+
+		pthread_join(thread1, NULL);
+		pthread_join(thread2, NULL);
+		munmap(huge_ptr, MMAP_SIZE);
+	}
+
+	return KSFT_PASS;
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 3e2bc818d566..9f53f7318a38 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -221,6 +221,10 @@ CATEGORY="hugetlb" run_test ./hugepage-mremap
 CATEGORY="hugetlb" run_test ./hugepage-vmemmap
 CATEGORY="hugetlb" run_test ./hugetlb-madvise
 
+# For this test, we need one and just one huge page
+echo 1 > /proc/sys/vm/nr_hugepages
+CATEGORY="hugetlb" run_test ./hugetlb_fault_after_madv
+
 if test_selected "hugetlb"; then
 	echo "NOTE: These hugetlb tests provide minimal coverage.  Use"
 	echo "      https://github.com/libhugetlbfs/libhugetlbfs.git for"
-- 
2.34.1