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, 148 insertions, 0 deletions

diff --git a/fs/fuse/req_timeout.c b/fs/fuse/req_timeout.c
new file mode 100644
index 000000000..6cc6fc491
--- /dev/null
+++ b/fs/fuse/req_timeout.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "dev.h"
+#include "sysctl.h"
+#include "fuse_dev_i.h"
+#include "dev_uring_i.h"
+
+/* Frequency (in seconds) of request timeout checks, if opted into */
+#define FUSE_TIMEOUT_TIMER_FREQ 15
+
+/* Frequency (in jiffies) of request timeout checks, if opted into */
+static const unsigned long fuse_timeout_timer_freq =
+	secs_to_jiffies(FUSE_TIMEOUT_TIMER_FREQ);
+
+/*
+ * Default timeout (in seconds) for the server to reply to a request
+ * before the connection is aborted, if no timeout was specified on mount.
+ *
+ * Exported via sysctl
+ */
+unsigned int fuse_default_req_timeout;
+
+/*
+ * Max timeout (in seconds) for the server to reply to a request before
+ * the connection is aborted.
+ *
+ * Exported via sysctl
+ */
+unsigned int fuse_max_req_timeout;
+
+bool fuse_request_expired(struct fuse_chan *fch, struct list_head *list)
+{
+	struct fuse_req *req;
+
+	req = list_first_entry_or_null(list, struct fuse_req, list);
+	if (!req)
+		return false;
+	return time_is_before_jiffies(req->create_time + fch->timeout.req_timeout);
+}
+
+static bool fuse_fpq_processing_expired(struct fuse_chan *fch, struct list_head *processing)
+{
+	int i;
+
+	for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
+		if (fuse_request_expired(fch, &processing[i]))
+			return true;
+
+	return false;
+}
+
+/*
+ * Check if any requests aren't being completed by the time the request timeout
+ * elapses. To do so, we:
+ * - check the fiq pending list
+ * - check the bg queue
+ * - check the fpq io and processing lists
+ *
+ * To make this fast, we only check against the head request on each list since
+ * these are generally queued in order of creation time (eg newer requests get
+ * queued to the tail). We might miss a few edge cases (eg requests transitioning
+ * between lists, re-sent requests at the head of the pending list having a
+ * later creation time than other requests on that list, etc.) but that is fine
+ * since if the request never gets fulfilled, it will eventually be caught.
+ */
+static void fuse_check_timeout(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct fuse_chan *fch = container_of(dwork, struct fuse_chan, timeout.work);
+	struct fuse_iqueue *fiq = &fch->iq;
+	struct fuse_dev *fud;
+	struct fuse_pqueue *fpq;
+	bool expired = false;
+
+	if (!atomic_read(&fch->num_waiting))
+		goto out;
+
+	spin_lock(&fiq->lock);
+	expired = fuse_request_expired(fch, &fiq->pending);
+	spin_unlock(&fiq->lock);
+	if (expired)
+		goto chan_abort;
+
+	spin_lock(&fch->bg_lock);
+	expired = fuse_request_expired(fch, &fch->bg_queue);
+	spin_unlock(&fch->bg_lock);
+	if (expired)
+		goto chan_abort;
+
+	spin_lock(&fch->lock);
+	if (!fch->connected) {
+		spin_unlock(&fch->lock);
+		return;
+	}
+	list_for_each_entry(fud, &fch->devices, entry) {
+		fpq = &fud->pq;
+		spin_lock(&fpq->lock);
+		if (fuse_request_expired(fch, &fpq->io) ||
+		    fuse_fpq_processing_expired(fch, fpq->processing)) {
+			spin_unlock(&fpq->lock);
+			spin_unlock(&fch->lock);
+			goto chan_abort;
+		}
+
+		spin_unlock(&fpq->lock);
+	}
+	spin_unlock(&fch->lock);
+
+	if (fuse_uring_request_expired(fch))
+		goto chan_abort;
+
+out:
+	queue_delayed_work(system_percpu_wq, &fch->timeout.work,
+			   fuse_timeout_timer_freq);
+	return;
+
+chan_abort:
+	fuse_chan_abort(fch, false);
+}
+
+static void set_request_timeout(struct fuse_chan *fch, unsigned int timeout)
+{
+	fch->timeout.req_timeout = secs_to_jiffies(timeout);
+	INIT_DELAYED_WORK(&fch->timeout.work, fuse_check_timeout);
+	queue_delayed_work(system_percpu_wq, &fch->timeout.work,
+			   fuse_timeout_timer_freq);
+}
+
+void fuse_init_server_timeout(struct fuse_chan *fch, unsigned int timeout)
+{
+	if (!timeout && !fuse_max_req_timeout && !fuse_default_req_timeout)
+		return;
+
+	if (!timeout)
+		timeout = fuse_default_req_timeout;
+
+	if (fuse_max_req_timeout) {
+		if (timeout)
+			timeout = min(fuse_max_req_timeout, timeout);
+		else
+			timeout = fuse_max_req_timeout;
+	}
+
+	timeout = max(FUSE_TIMEOUT_TIMER_FREQ, timeout);
+
+	set_request_timeout(fch, timeout);
+}
+