Re: [PATCH v1 net 3/3] selftest: net: Check wraparounds for sk->sk_rmem_alloc.

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: Mon, 24 Mar 2025 11:58:06 -0400

quoted

+TEST_F(so_rcvbuf, rmem_max)
+{
+	char buf[16] = {};
+	int ret, i;
+
+	create_socketpair(_metadata, self, variant);
+
+	ret = setsockopt(self->server, SOL_SOCKET, SO_RCVBUFFORCE,
+			 &(int){INT_MAX}, sizeof(int));
+	ASSERT_EQ(ret, 0);
+
+	ASSERT_EQ(get_prot_pages(_metadata, variant), 0);
+
+	for (i = 1; ; i++) {
+		ret = send(self->client, buf, sizeof(buf), 0);
+		ASSERT_EQ(ret, sizeof(buf));
+
+		if (i % 10000 == 0) {
+			int pages = get_prot_pages(_metadata, variant);
+
+			/* sk_rmem_alloc wrapped around too much ? */
+			ASSERT_LE(pages, *variant->max_pages);
+
+			if (pages == *variant->max_pages)
+				break;

Does correctness depend here on max_pages being a multiple of 10K?

10K may be too conservative, but at least we need to ensure
that the size of accumulated skbs exceeds 1 PAGE_SIZE to
fail on the ASSERT_LE(), otherwise we can't detect the multiple
wraparounds even without patch 1.

The later sleep for call_rcu() was dominant than this loop on
my machine.

Thanks!