selftests/mm: add a new test for madv and hugetlb

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

Link: https://lkml.kernel.org/r/20231005163922.87568-3-leitao@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Tested-by: Rik van Riel <riel@surriel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 2a89989..78dfec8 100644 (file)
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -69,6 +69,7 @@ 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 (file)
index 0000000..73b81c6
--- /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 45941ad..bf4c4cd 100755 (executable)
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -223,6 +223,10 @@ 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"