linux-kernel - [PATCH 1/3] selftests/mm: virtual_address_range: Fix error when CommitLimit

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Message-Id: <20250107-virtual_address_range-tests-v1-1-3834a2fb47fe@linutronix.de>
Date: Tue, 07 Jan 2025 16:14:45 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Shuah Khan <shuah@...nel.org>, Dev Jain <dev.jain@....com>, 
 Thomas Gleixner <tglx@...utronix.de>
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
 stable@...r.kernel.org
Subject: [PATCH 1/3] selftests/mm: virtual_address_range: Fix error when
 CommitLimit < 1GiB

If not enough physical memory is available the kernel may fail mmap();
see __vm_enough_memory() and vm_commit_limit().
In that case the logic in validate_complete_va_space() does not make
sense and will even incorrectly fail.
Instead skip the test if no mmap() succeeded.

Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Cc: stable@...r.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>

---
The logic in __vm_enough_memory() seems weird.
It describes itself as "Check that a process has enough memory to
allocate a new virtual mapping", however it never checks the current
memory usage of the process.
So it only disallows large mappings. But many small mappings taking the
same amount of memory are allowed; and then even automatically merged
into one big mapping.
---
 tools/testing/selftests/mm/virtual_address_range.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
index 2a2b69e91950a37999f606847c9c8328d79890c2..d7bf8094d8bcd4bc96e2db4dc3fcb41968def859 100644
--- a/tools/testing/selftests/mm/virtual_address_range.c
+++ b/tools/testing/selftests/mm/virtual_address_range.c
@@ -178,6 +178,12 @@ int main(int argc, char *argv[])
 		validate_addr(ptr[i], 0);
 	}
 	lchunks = i;
+
+	if (!lchunks) {
+		ksft_test_result_skip("Not enough memory for a single chunk\n");
+		ksft_finished();
+	}
+
 	hptr = (char **) calloc(NR_CHUNKS_HIGH, sizeof(char *));
 	if (hptr == NULL) {
 		ksft_test_result_skip("Memory constraint not fulfilled\n");

-- 
2.47.1