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, 297 insertions, 0 deletions

diff --git a/fs/lockd/clntlock.c b/fs/lockd/clntlock.c
new file mode 100644
index 000000000..f797cc99f
--- /dev/null
+++ b/fs/lockd/clntlock.c
@@ -0,0 +1,297 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/fs/lockd/clntlock.c
+ *
+ * Lock handling for the client side NLM implementation
+ *
+ * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/time.h>
+#include <linux/nfs_fs.h>
+#include <linux/sunrpc/addr.h>
+#include <linux/sunrpc/svc.h>
+#include <linux/sunrpc/svc_xprt.h>
+#include <linux/kthread.h>
+
+#include "lockd.h"
+#include "trace.h"
+
+#define NLMDBG_FACILITY		NLMDBG_CLIENT
+
+/*
+ * Local function prototypes
+ */
+static int			reclaimer(void *ptr);
+
+/*
+ * The following functions handle blocking and granting from the
+ * client perspective.
+ */
+
+static LIST_HEAD(nlm_blocked);
+static DEFINE_SPINLOCK(nlm_blocked_lock);
+
+/**
+ * nlmclnt_init - Set up per-NFS mount point lockd data structures
+ * @nlm_init: pointer to arguments structure
+ *
+ * Returns pointer to an appropriate nlm_host struct,
+ * or an ERR_PTR value.
+ */
+struct nlm_host *nlmclnt_init(const struct nlmclnt_initdata *nlm_init)
+{
+	struct nlm_host *host;
+	u32 nlm_version = (nlm_init->nfs_version == 2) ? 1 : 4;
+	int status;
+
+	status = lockd_up(nlm_init->net, nlm_init->cred);
+	if (status < 0)
+		return ERR_PTR(status);
+
+	host = nlmclnt_lookup_host(nlm_init->address, nlm_init->addrlen,
+				   nlm_init->protocol, nlm_version,
+				   nlm_init->hostname, nlm_init->noresvport,
+				   nlm_init->net, nlm_init->cred);
+	if (host == NULL)
+		goto out_nohost;
+	if (host->h_rpcclnt == NULL && nlm_bind_host(host) == NULL)
+		goto out_nobind;
+
+	host->h_nlmclnt_ops = nlm_init->nlmclnt_ops;
+	return host;
+out_nobind:
+	nlmclnt_release_host(host);
+out_nohost:
+	lockd_down(nlm_init->net);
+	return ERR_PTR(-ENOLCK);
+}
+EXPORT_SYMBOL_GPL(nlmclnt_init);
+
+/**
+ * nlmclnt_done - Release resources allocated by nlmclnt_init()
+ * @host: nlm_host structure reserved by nlmclnt_init()
+ *
+ */
+void nlmclnt_done(struct nlm_host *host)
+{
+	struct net *net = host->net;
+
+	nlmclnt_release_host(host);
+	lockd_down(net);
+}
+EXPORT_SYMBOL_GPL(nlmclnt_done);
+
+void nlmclnt_prepare_block(struct nlm_wait *block, struct nlm_host *host, struct file_lock *fl)
+{
+	block->b_host = host;
+	block->b_lock = fl;
+	init_waitqueue_head(&block->b_wait);
+	block->b_status = nlm_lck_blocked;
+}
+
+struct rpc_clnt *nlmclnt_rpc_clnt(struct nlm_host *host)
+{
+	return host->h_rpcclnt;
+}
+EXPORT_SYMBOL_GPL(nlmclnt_rpc_clnt);
+
+/*
+ * Queue up a lock for blocking so that the GRANTED request can see it
+ */
+void nlmclnt_queue_block(struct nlm_wait *block)
+{
+	spin_lock(&nlm_blocked_lock);
+	list_add(&block->b_list, &nlm_blocked);
+	spin_unlock(&nlm_blocked_lock);
+}
+
+/*
+ * Dequeue the block and return its final status
+ */
+__be32 nlmclnt_dequeue_block(struct nlm_wait *block)
+{
+	__be32 status;
+
+	spin_lock(&nlm_blocked_lock);
+	list_del(&block->b_list);
+	status = block->b_status;
+	spin_unlock(&nlm_blocked_lock);
+	return status;
+}
+
+/*
+ * Block on a lock
+ */
+int nlmclnt_wait(struct nlm_wait *block, struct nlm_rqst *req, long timeout)
+{
+	long ret;
+
+	/* A borken server might ask us to block even if we didn't
+	 * request it. Just say no!
+	 */
+	if (block == NULL)
+		return -EAGAIN;
+
+	/* Go to sleep waiting for GRANT callback. Some servers seem
+	 * to lose callbacks, however, so we're going to poll from
+	 * time to time just to make sure.
+	 *
+	 * For now, the retry frequency is pretty high; normally 
+	 * a 1 minute timeout would do. See the comment before
+	 * nlmclnt_lock for an explanation.
+	 */
+	ret = wait_event_interruptible_timeout(block->b_wait,
+			block->b_status != nlm_lck_blocked,
+			timeout);
+	if (ret < 0)
+		return -ERESTARTSYS;
+	/* Reset the lock status after a server reboot so we resend */
+	if (block->b_status == nlm_lck_denied_grace_period)
+		block->b_status = nlm_lck_blocked;
+	return 0;
+}
+
+/*
+ * The server lockd has called us back to tell us the lock was granted
+ */
+__be32 nlmclnt_grant(const struct sockaddr *addr, const struct lockd_lock *lock)
+{
+	const struct file_lock *fl = &lock->fl;
+	const struct nfs_fh *fh = &lock->fh;
+	struct nlm_wait	*block;
+	__be32 res = nlm_lck_denied;
+
+	/*
+	 * Look up blocked request based on arguments. 
+	 * Warning: must not use cookie to match it!
+	 */
+	spin_lock(&nlm_blocked_lock);
+	list_for_each_entry(block, &nlm_blocked, b_list) {
+		struct file_lock *fl_blocked = block->b_lock;
+
+		if (fl_blocked->fl_start != fl->fl_start)
+			continue;
+		if (fl_blocked->fl_end != fl->fl_end)
+			continue;
+		/*
+		 * Careful! The NLM server will return the 32-bit "pid" that
+		 * we put on the wire: in this case the lockowner "pid".
+		 */
+		if (fl_blocked->fl_u.nfs_fl.owner->pid != lock->svid)
+			continue;
+		if (!rpc_cmp_addr(nlm_addr(block->b_host), addr))
+			continue;
+		if (nfs_compare_fh(NFS_FH(file_inode(fl_blocked->c.flc_file)), fh) != 0)
+			continue;
+		/* Alright, we found a lock. Set the return status
+		 * and wake up the caller
+		 */
+		block->b_status = nlm_granted;
+		wake_up(&block->b_wait);
+		res = nlm_granted;
+	}
+	spin_unlock(&nlm_blocked_lock);
+	trace_nlmclnt_grant(lock, addr, svc_addr_len(addr), res);
+	return res;
+}
+
+/*
+ * The following procedures deal with the recovery of locks after a
+ * server crash.
+ */
+
+/*
+ * Reclaim all locks on server host. We do this by spawning a separate
+ * reclaimer thread.
+ */
+void
+nlmclnt_recovery(struct nlm_host *host)
+{
+	struct task_struct *task;
+
+	if (!host->h_reclaiming++) {
+		nlm_get_host(host);
+		task = kthread_run(reclaimer, host, "%s-reclaim", host->h_name);
+		if (IS_ERR(task))
+			printk(KERN_ERR "lockd: unable to spawn reclaimer "
+				"thread. Locks for %s won't be reclaimed! "
+				"(%ld)\n", host->h_name, PTR_ERR(task));
+	}
+}
+
+static int
+reclaimer(void *ptr)
+{
+	struct nlm_host	  *host = (struct nlm_host *) ptr;
+	struct nlm_wait	  *block;
+	struct nlm_rqst   *req;
+	struct file_lock *fl, *next;
+	u32 nsmstate;
+	struct net *net = host->net;
+
+	req = kmalloc_obj(*req);
+	if (!req)
+		return 0;
+
+	allow_signal(SIGKILL);
+
+	down_write(&host->h_rwsem);
+	lockd_up(net, NULL);	/* note: this cannot fail as lockd is already running */
+
+	dprintk("lockd: reclaiming locks for host %s\n", host->h_name);
+
+restart:
+	nsmstate = host->h_nsmstate;
+
+	/* Force a portmap getport - the peer's lockd will
+	 * most likely end up on a different port.
+	 */
+	host->h_nextrebind = jiffies;
+	nlm_rebind_host(host);
+
+	/* First, reclaim all locks that have been granted. */
+	list_splice_init(&host->h_granted, &host->h_reclaim);
+	list_for_each_entry_safe(fl, next, &host->h_reclaim, fl_u.nfs_fl.list) {
+		list_del_init(&fl->fl_u.nfs_fl.list);
+
+		/*
+		 * sending this thread a SIGKILL will result in any unreclaimed
+		 * locks being removed from the h_granted list. This means that
+		 * the kernel will not attempt to reclaim them again if a new
+		 * reclaimer thread is spawned for this host.
+		 */
+		if (signalled())
+			continue;
+		if (nlmclnt_reclaim(host, fl, req) != 0)
+			continue;
+		list_add_tail(&fl->fl_u.nfs_fl.list, &host->h_granted);
+		if (host->h_nsmstate != nsmstate) {
+			/* Argh! The server rebooted again! */
+			goto restart;
+		}
+	}
+
+	host->h_reclaiming = 0;
+	up_write(&host->h_rwsem);
+	dprintk("NLM: done reclaiming locks for host %s\n", host->h_name);
+
+	/* Now, wake up all processes that sleep on a blocked lock */
+	spin_lock(&nlm_blocked_lock);
+	list_for_each_entry(block, &nlm_blocked, b_list) {
+		if (block->b_host == host) {
+			block->b_status = nlm_lck_denied_grace_period;
+			wake_up(&block->b_wait);
+		}
+	}
+	spin_unlock(&nlm_blocked_lock);
+
+	/* Release host handle after use */
+	nlmclnt_release_host(host);
+	lockd_down(net);
+	kfree(req);
+	return 0;
+}