Fix thread constructor test on newer kernels (#28613)

Works around and closes https://github.com/dotnet/coreclr/issues/17170
- Works around an issue on linux-arm64 where pthread_create appears to reserve less stack space than requested without failing, and limits the max reserved stack size to the ulimit-configued value, leading to seg fault when the requested size of stack space is attempted to be used
- Fixed to write every page in the stack region that is being checked, to guarantee hitting the guard page in case of failure. The JIT's stack probe for stackalloc should cover this, https://github.com/dotnet/coreclr/issues/16827 details why that was not happening, in any case this test is not intended to test stack probing behavior, so this change makes the test a bit stronger in what it actually intends to test.

Author: kouvel

src/System.Threading.Thread/tests/ThreadTests.cs

@@ -26,6 +26,11 @@ public static partial class ThreadTests
         [Fact]
         public static void ConstructorTest()
         {
+            const int SmallStackSize = 64 << 10; // 64 KB, currently accepted in all supported platforms, and is the PAL minimum
+            const int LargeStackSize = 2 << 20; // 2 MB, see https://github.com/dotnet/coreclr/issues/17170
+
+            int pageSizeBytes = Environment.SystemPageSize;
+
             Action<Thread> startThreadAndJoin =
                 t =>
                 {
@@ -38,22 +43,25 @@ public static void ConstructorTest()
                 {
                     // Try to stack-allocate an array to verify that close to the expected amount of stack space is actually
                     // available
-                    int bufferSizeBytes = Math.Max(16 << 10, stackSizeBytes - (64 << 10));
+                    int bufferSizeBytes = Math.Max(16 << 10, stackSizeBytes - SmallStackSize);
                     unsafe
                     {
                         byte* buffer = stackalloc byte[bufferSizeBytes];
-                        Volatile.Write(ref buffer[0], 0xff);
+                        for (int i = 0; i < bufferSizeBytes; i += pageSizeBytes)
+                        {
+                            Volatile.Write(ref buffer[i], 0xff);
+                        }
                         Volatile.Write(ref buffer[bufferSizeBytes - 1], 0xff);
                     }
                 };
             startThreadAndJoin(new Thread(() => verifyStackSize(0)));
             startThreadAndJoin(new Thread(() => verifyStackSize(0), 0));
-            startThreadAndJoin(new Thread(() => verifyStackSize(64 << 10), 64 << 10)); // 64 KB
-            startThreadAndJoin(new Thread(() => verifyStackSize(16 << 20), 16 << 20)); // 16 MB
+            startThreadAndJoin(new Thread(() => verifyStackSize(SmallStackSize), SmallStackSize));
+            startThreadAndJoin(new Thread(() => verifyStackSize(LargeStackSize), LargeStackSize));
             startThreadAndJoin(new Thread(state => verifyStackSize(0)));
             startThreadAndJoin(new Thread(state => verifyStackSize(0), 0));
-            startThreadAndJoin(new Thread(state => verifyStackSize(64 << 10), 64 << 10)); // 64 KB
-            startThreadAndJoin(new Thread(state => verifyStackSize(16 << 20), 16 << 20)); // 16 MB
+            startThreadAndJoin(new Thread(state => verifyStackSize(SmallStackSize), SmallStackSize));
+            startThreadAndJoin(new Thread(state => verifyStackSize(LargeStackSize), LargeStackSize));
 
             Assert.Throws<ArgumentNullException>(() => new Thread((ThreadStart)null));
             Assert.Throws<ArgumentNullException>(() => new Thread((ThreadStart)null, 0));