[PATCH] hugemmap/hugemmap35: migrate libhugetlbfs test truncate_reserve_wraparound.c

This test verifies that the kernel correctly maintains hugepage reservation
accounting when truncating a hugetlbfs file. It ensures that reserved
hugepages are properly tracked through the complete lifecycle

Signed-off-by: Pavithra <[email protected]>
---
 runtest/hugetlb                               |   1 +
 testcases/kernel/mem/.gitignore               |   1 +
 .../kernel/mem/hugetlb/hugemmap/hugemmap38.c  | 128 ++++++++++++++++++
 3 files changed, 130 insertions(+)
 create mode 100644 testcases/kernel/mem/hugetlb/hugemmap/hugemmap38.c

diff --git a/runtest/hugetlb b/runtest/hugetlb
index 8ee0e6f82..9dbee8555 100644
--- a/runtest/hugetlb
+++ b/runtest/hugetlb
@@ -37,6 +37,7 @@ hugemmap31 hugemmap31
 hugemmap32 hugemmap32
 hugemmap34 hugemmap34
 hugemmap35 hugemmap35
+hugemmap38 hugemmap38
 hugemmap05_1 hugemmap05 -m
 hugemmap05_2 hugemmap05 -s
 hugemmap05_3 hugemmap05 -s -m
diff --git a/testcases/kernel/mem/.gitignore b/testcases/kernel/mem/.gitignore
index 0e59035df..0e9547d99 100644
--- a/testcases/kernel/mem/.gitignore
+++ b/testcases/kernel/mem/.gitignore
@@ -37,6 +37,7 @@
 /hugetlb/hugemmap/hugemmap32
 /hugetlb/hugemmap/hugemmap34
 /hugetlb/hugemmap/hugemmap35
+/hugetlb/hugemmap/hugemmap38
 /hugetlb/hugeshmat/hugeshmat01
 /hugetlb/hugeshmat/hugeshmat02
 /hugetlb/hugeshmat/hugeshmat03
diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap38.c b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap38.c
new file mode 100644
index 000000000..4cefb5f78
--- /dev/null
+++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap38.c
@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+/*
+ * Copyright (C) 2005-2006 David Gibson & Adam Litke, IBM Corporation.
+ * Copyright (c) 2026 Pavithra <[email protected]>
+ */
+
+/*
+ * Origin: https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/truncate_reserve_wraparound.c
+ */
+
+/*\
+ * Test that hugepage reservation accounting is correctly maintained when
+ * truncating a hugetlbfs file. This verifies that reserved hugepages are
+ * properly tracked through the sequence of: mmap (reserves page), touch
+ * (instantiates page), truncate (releases page), and attempted access
+ * (triggers SIGBUS). A bug in i_size handling could cause the reservation
+ * count to become incorrect, leading to resource leaks or allocation failures.
+ *
+ * Requires root to mount hugetlbfs.
+ */
+
+#include <signal.h>
+#include <setjmp.h>
+#include "hugetlb.h"
+
+#define MNTPOINT "hugetlbfs/"
+
+static long hpage_size;
+static int fd = -1;
+
+static sigjmp_buf sig_escape;
+
+static void sigbus_handler(int signum LTP_ATTRIBUTE_UNUSED)
+{
+	siglongjmp(sig_escape, 17);
+}
+
+static void run_test(void)
+{
+	volatile int sigbus_count = 0;
+	unsigned long initial_rsvd, after_map_rsvd, after_touch_rsvd;
+	unsigned long after_trunc_rsvd, after_unmap_rsvd, after_sigbus_rsvd;
+	volatile unsigned int *q;
+	void *p;
+
+	initial_rsvd = SAFE_READ_MEMINFO(MEMINFO_HPAGE_RSVD);
+	tst_res(TINFO, "Reserve count before map: %lu", initial_rsvd);
+
+	p = SAFE_MMAP(NULL, hpage_size, PROT_READ|PROT_WRITE, MAP_SHARED,
+			fd, 0);
+	q = p;
+
+	after_map_rsvd = SAFE_READ_MEMINFO(MEMINFO_HPAGE_RSVD);
+
+	TST_EXP_EQ_LU(initial_rsvd + 1, after_map_rsvd);
+	if (!TST_PASS)
+		goto windup;
+
+	*q = 0;
+	after_touch_rsvd = SAFE_READ_MEMINFO(MEMINFO_HPAGE_RSVD);
+
+	TST_EXP_EQ_LU(initial_rsvd, after_touch_rsvd);
+	if (!TST_PASS)
+		goto windup;
+
+	SAFE_FTRUNCATE(fd, 0);
+	after_trunc_rsvd = SAFE_READ_MEMINFO(MEMINFO_HPAGE_RSVD);
+
+	TST_EXP_EQ_LU(initial_rsvd, after_trunc_rsvd);
+	if (!TST_PASS)
+		goto windup;
+
+	if (sigsetjmp(sig_escape, 1) == 0)
+		*q; /* Fault, triggering a SIGBUS */
+	else
+		sigbus_count++;
+
+	if (sigbus_count != 1) {
+		tst_res(TFAIL, "Didn't SIGBUS after truncate");
+		goto windup;
+	}
+
+	after_sigbus_rsvd = SAFE_READ_MEMINFO(MEMINFO_HPAGE_RSVD);
+
+	TST_EXP_EQ_LU(initial_rsvd, after_sigbus_rsvd);
+	if (!TST_PASS)
+		goto windup;
+
+windup:
+	SAFE_MUNMAP(p, hpage_size);
+	after_unmap_rsvd = SAFE_READ_MEMINFO(MEMINFO_HPAGE_RSVD);
+
+	TST_EXP_EQ_LU(initial_rsvd, after_unmap_rsvd);
+}
+
+static void setup(void)
+{
+
+	hpage_size = tst_get_hugepage_size();
+	fd = tst_creat_unlinked(MNTPOINT, 0, 0600);
+
+	struct sigaction sa = {
+		.sa_handler = sigbus_handler,
+		.sa_flags = 0,
+	};
+
+	SAFE_SIGACTION(SIGBUS, &sa, NULL);
+}
+
+static void cleanup(void)
+{
+	if (fd != -1)
+		SAFE_CLOSE(fd);
+}
+
+static struct tst_test test = {
+	.tags = (struct tst_tag[]) {
+		{"linux-git", "ebed4bfc8da8"},
+		{}
+	},
+	.needs_root = 1,
+	.mntpoint = MNTPOINT,
+	.needs_hugetlbfs = 1,
+	.hugepages = {4, TST_NEEDS},
+	.setup = setup,
+	.cleanup = cleanup,
+	.test_all = run_test,
+};
-- 
2.55.0


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