ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 72 insertions, 0 deletions

diff --git a/sound/firewire/lib.c b/sound/firewire/lib.c
new file mode 100644
index 000000000..654e1a605
--- /dev/null
+++ b/sound/firewire/lib.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * miscellaneous helper functions
+ *
+ * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
+ */
+
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/firewire.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include "lib.h"
+
+#define ERROR_RETRY_DELAY_MS	20
+
+/**
+ * snd_fw_transaction - send a request and wait for its completion
+ * @unit: the driver's unit on the target device
+ * @tcode: the transaction code
+ * @offset: the address in the target's address space
+ * @buffer: input/output data
+ * @length: length of @buffer
+ * @flags: use %FW_FIXED_GENERATION and add the generation value to attempt the
+ *         request only in that generation; use %FW_QUIET to suppress error
+ *         messages
+ *
+ * Submits an asynchronous request to the target device, and waits for the
+ * response.  The node ID and the current generation are derived from @unit.
+ * On a bus reset or an error, the transaction is retried a few times.
+ * Returns zero on success, or a negative error code.
+ */
+int snd_fw_transaction(struct fw_unit *unit, int tcode,
+		       u64 offset, void *buffer, size_t length,
+		       unsigned int flags)
+{
+	struct fw_device *device = fw_parent_device(unit);
+	int generation, rcode, tries = 0;
+
+	generation = flags & FW_GENERATION_MASK;
+	for (;;) {
+		if (!(flags & FW_FIXED_GENERATION)) {
+			generation = device->generation;
+			smp_rmb(); /* node_id vs. generation */
+		}
+		rcode = fw_run_transaction(device->card, tcode,
+					   device->node_id, generation,
+					   device->max_speed, offset,
+					   buffer, length);
+
+		if (rcode == RCODE_COMPLETE)
+			return 0;
+
+		if (rcode == RCODE_GENERATION && (flags & FW_FIXED_GENERATION))
+			return -EAGAIN;
+
+		if (rcode_is_permanent_error(rcode) || ++tries >= 3) {
+			if (!(flags & FW_QUIET))
+				dev_err(&unit->device,
+					"transaction failed: %s\n",
+					fw_rcode_string(rcode));
+			return -EIO;
+		}
+
+		msleep(ERROR_RETRY_DELAY_MS);
+	}
+}
+EXPORT_SYMBOL(snd_fw_transaction);
+
+MODULE_DESCRIPTION("FireWire audio helper functions");
+MODULE_AUTHOR("Clemens Ladisch <clemens@ladisch.de>");
+MODULE_LICENSE("GPL");