kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 311 insertions, 0 deletions

diff --git a/net/rds/threads.c b/net/rds/threads.c
new file mode 100644
index 000000000..639302bab
--- /dev/null
+++ b/net/rds/threads.c
@@ -0,0 +1,311 @@
+/*
+ * Copyright (c) 2006, 2018 Oracle and/or its affiliates. All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/random.h>
+#include <linux/export.h>
+
+#include "rds.h"
+
+/*
+ * All of connection management is simplified by serializing it through
+ * work queues that execute in a connection managing thread.
+ *
+ * TCP wants to send acks through sendpage() in response to data_ready(),
+ * but it needs a process context to do so.
+ *
+ * The receive paths need to allocate but can't drop packets (!) so we have
+ * a thread around to block allocating if the receive fast path sees an
+ * allocation failure.
+ */
+
+/* Grand Unified Theory of connection life cycle:
+ * At any point in time, the connection can be in one of these states:
+ * DOWN, CONNECTING, UP, DISCONNECTING, ERROR
+ *
+ * The following transitions are possible:
+ *  ANY		  -> ERROR
+ *  UP		  -> DISCONNECTING
+ *  ERROR	  -> DISCONNECTING
+ *  DISCONNECTING -> DOWN
+ *  DOWN	  -> CONNECTING
+ *  CONNECTING	  -> UP
+ *
+ * Transition to state DISCONNECTING/DOWN:
+ *  -	Inside the shutdown worker; synchronizes with xmit path
+ *	through RDS_IN_XMIT, and with connection management callbacks
+ *	via c_cm_lock.
+ *
+ *	For receive callbacks, we rely on the underlying transport
+ *	(TCP, IB/RDMA) to provide the necessary synchronisation.
+ */
+struct workqueue_struct *rds_wq;
+EXPORT_SYMBOL_GPL(rds_wq);
+
+void rds_connect_path_complete(struct rds_conn_path *cp, int curr)
+{
+	if (!rds_conn_path_transition(cp, curr, RDS_CONN_UP)) {
+		printk(KERN_WARNING "%s: Cannot transition to state UP, "
+				"current state is %d\n",
+				__func__,
+				atomic_read(&cp->cp_state));
+		rds_conn_path_drop(cp, false);
+		return;
+	}
+
+	rdsdebug("conn %p for %pI6c to %pI6c complete\n",
+		 cp->cp_conn, &cp->cp_conn->c_laddr, &cp->cp_conn->c_faddr);
+
+	cp->cp_reconnect_jiffies = 0;
+	set_bit(0, &cp->cp_conn->c_map_queued);
+	rcu_read_lock();
+	if (!rds_destroy_pending(cp->cp_conn)) {
+		queue_delayed_work(cp->cp_wq, &cp->cp_send_w, 0);
+		queue_delayed_work(cp->cp_wq, &cp->cp_recv_w, 0);
+	}
+	rcu_read_unlock();
+	cp->cp_conn->c_proposed_version = RDS_PROTOCOL_VERSION;
+}
+EXPORT_SYMBOL_GPL(rds_connect_path_complete);
+
+void rds_connect_complete(struct rds_connection *conn)
+{
+	rds_connect_path_complete(&conn->c_path[0], RDS_CONN_CONNECTING);
+}
+EXPORT_SYMBOL_GPL(rds_connect_complete);
+
+/*
+ * This random exponential backoff is relied on to eventually resolve racing
+ * connects.
+ *
+ * If connect attempts race then both parties drop both connections and come
+ * here to wait for a random amount of time before trying again.  Eventually
+ * the backoff range will be so much greater than the time it takes to
+ * establish a connection that one of the pair will establish the connection
+ * before the other's random delay fires.
+ *
+ * Connection attempts that arrive while a connection is already established
+ * are also considered to be racing connects.  This lets a connection from
+ * a rebooted machine replace an existing stale connection before the transport
+ * notices that the connection has failed.
+ *
+ * We should *always* start with a random backoff; otherwise a broken connection
+ * will always take several iterations to be re-established.
+ */
+void rds_queue_reconnect(struct rds_conn_path *cp)
+{
+	unsigned long rand;
+	struct rds_connection *conn = cp->cp_conn;
+
+	rdsdebug("conn %p for %pI6c to %pI6c reconnect jiffies %lu\n",
+		 conn, &conn->c_laddr, &conn->c_faddr,
+		 cp->cp_reconnect_jiffies);
+
+	/* let peer with smaller addr initiate reconnect, to avoid duels */
+	if (conn->c_trans->t_type == RDS_TRANS_TCP &&
+	    rds_addr_cmp(&conn->c_laddr, &conn->c_faddr) >= 0)
+		return;
+
+	set_bit(RDS_RECONNECT_PENDING, &cp->cp_flags);
+	if (cp->cp_reconnect_jiffies == 0) {
+		cp->cp_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
+		rcu_read_lock();
+		if (!rds_destroy_pending(cp->cp_conn))
+			queue_delayed_work(cp->cp_wq, &cp->cp_conn_w, 0);
+		rcu_read_unlock();
+		return;
+	}
+
+	get_random_bytes(&rand, sizeof(rand));
+	rdsdebug("%lu delay %lu ceil conn %p for %pI6c -> %pI6c\n",
+		 rand % cp->cp_reconnect_jiffies, cp->cp_reconnect_jiffies,
+		 conn, &conn->c_laddr, &conn->c_faddr);
+	rcu_read_lock();
+	if (!rds_destroy_pending(cp->cp_conn))
+		queue_delayed_work(cp->cp_wq, &cp->cp_conn_w,
+				   rand % cp->cp_reconnect_jiffies);
+	rcu_read_unlock();
+
+	cp->cp_reconnect_jiffies = min(cp->cp_reconnect_jiffies * 2,
+					rds_sysctl_reconnect_max_jiffies);
+}
+
+void rds_connect_worker(struct work_struct *work)
+{
+	struct rds_conn_path *cp = container_of(work,
+						struct rds_conn_path,
+						cp_conn_w.work);
+	struct rds_connection *conn = cp->cp_conn;
+	int ret;
+
+	if (cp->cp_index > 0 &&
+	    rds_addr_cmp(&cp->cp_conn->c_laddr, &cp->cp_conn->c_faddr) >= 0)
+		return;
+	clear_bit(RDS_RECONNECT_PENDING, &cp->cp_flags);
+	ret = rds_conn_path_transition(cp, RDS_CONN_DOWN, RDS_CONN_CONNECTING);
+	if (ret) {
+		ret = conn->c_trans->conn_path_connect(cp);
+		rdsdebug("conn %p for %pI6c to %pI6c dispatched, ret %d\n",
+			 conn, &conn->c_laddr, &conn->c_faddr, ret);
+
+		if (ret) {
+			if (rds_conn_path_transition(cp,
+						     RDS_CONN_CONNECTING,
+						     RDS_CONN_DOWN))
+				rds_queue_reconnect(cp);
+			else
+				rds_conn_path_error(cp, "connect failed\n");
+		}
+	}
+}
+
+void rds_send_worker(struct work_struct *work)
+{
+	struct rds_conn_path *cp = container_of(work,
+						struct rds_conn_path,
+						cp_send_w.work);
+	int ret;
+
+	if (rds_conn_path_state(cp) == RDS_CONN_UP) {
+		clear_bit(RDS_LL_SEND_FULL, &cp->cp_flags);
+		ret = rds_send_xmit(cp);
+		cond_resched();
+		rdsdebug("conn %p ret %d\n", cp->cp_conn, ret);
+		switch (ret) {
+		case -EAGAIN:
+			rds_stats_inc(s_send_immediate_retry);
+			queue_delayed_work(cp->cp_wq, &cp->cp_send_w, 0);
+			break;
+		case -ENOMEM:
+			rds_stats_inc(s_send_delayed_retry);
+			queue_delayed_work(cp->cp_wq, &cp->cp_send_w, 2);
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+void rds_recv_worker(struct work_struct *work)
+{
+	struct rds_conn_path *cp = container_of(work,
+						struct rds_conn_path,
+						cp_recv_w.work);
+	int ret;
+
+	if (rds_conn_path_state(cp) == RDS_CONN_UP) {
+		ret = cp->cp_conn->c_trans->recv_path(cp);
+		rdsdebug("conn %p ret %d\n", cp->cp_conn, ret);
+		switch (ret) {
+		case -EAGAIN:
+			rds_stats_inc(s_recv_immediate_retry);
+			queue_delayed_work(cp->cp_wq, &cp->cp_recv_w, 0);
+			break;
+		case -ENOMEM:
+			rds_stats_inc(s_recv_delayed_retry);
+			queue_delayed_work(cp->cp_wq, &cp->cp_recv_w, 2);
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+void rds_shutdown_worker(struct work_struct *work)
+{
+	struct rds_conn_path *cp = container_of(work,
+						struct rds_conn_path,
+						cp_down_w);
+
+	rds_conn_shutdown(cp);
+}
+
+void rds_threads_exit(void)
+{
+	destroy_workqueue(rds_wq);
+}
+
+int rds_threads_init(void)
+{
+	rds_wq = create_singlethread_workqueue("krdsd");
+	if (!rds_wq)
+		return -ENOMEM;
+
+	return 0;
+}
+
+/* Compare two IPv6 addresses.  Return 0 if the two addresses are equal.
+ * Return 1 if the first is greater.  Return -1 if the second is greater.
+ */
+int rds_addr_cmp(const struct in6_addr *addr1,
+		 const struct in6_addr *addr2)
+{
+#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
+	const __be64 *a1, *a2;
+	u64 x, y;
+
+	a1 = (__be64 *)addr1;
+	a2 = (__be64 *)addr2;
+
+	if (*a1 != *a2) {
+		if (be64_to_cpu(*a1) < be64_to_cpu(*a2))
+			return -1;
+		else
+			return 1;
+	} else {
+		x = be64_to_cpu(*++a1);
+		y = be64_to_cpu(*++a2);
+		if (x < y)
+			return -1;
+		else if (x > y)
+			return 1;
+		else
+			return 0;
+	}
+#else
+	u32 a, b;
+	int i;
+
+	for (i = 0; i < 4; i++) {
+		if (addr1->s6_addr32[i] != addr2->s6_addr32[i]) {
+			a = ntohl(addr1->s6_addr32[i]);
+			b = ntohl(addr2->s6_addr32[i]);
+			if (a < b)
+				return -1;
+			else if (a > b)
+				return 1;
+		}
+	}
+	return 0;
+#endif
+}
+EXPORT_SYMBOL_GPL(rds_addr_cmp);