Thread (39 messages) 39 messages, 5 authors, 2024-01-17
STALE890d
Revisions (3)
  1. v1 [diff vs current]
  2. v2 current
  3. v3 [diff vs current]

[PATCH v2 11/17] tracing: Introduce kho serialization

From: Alexander Graf <graf@amazon.com>
Date: 2023-12-22 19:38:10
Also in: kexec, linux-arm-kernel, linux-devicetree, linux-doc, linux-mm, lkml
Subsystem: the rest, tracing · Maintainers: Linus Torvalds, Steven Rostedt, Masami Hiramatsu

We want to be able to transfer ftrace state from one kernel to the next.
To start off with, let's establish all the boiler plate to get a write
hook when KHO wants to serialize and fill out basic data.

Follow-up patches will fill in serialization of ring buffers and events.

Signed-off-by: Alexander Graf <graf@amazon.com>

---

v1 -> v2:

  - Remove ifdefs
---
 kernel/trace/trace.c | 47 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 199df497db07..6ec31879b4eb 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -32,6 +32,7 @@
 #include <linux/percpu.h>
 #include <linux/splice.h>
 #include <linux/kdebug.h>
+#include <linux/kexec.h>
 #include <linux/string.h>
 #include <linux/mount.h>
 #include <linux/rwsem.h>
@@ -866,6 +867,8 @@ static struct tracer		*trace_types __read_mostly;
  */
 DEFINE_MUTEX(trace_types_lock);
 
+static bool trace_in_kho;
+
 /*
  * serialize the access of the ring buffer
  *
@@ -10560,12 +10563,56 @@ void __init early_trace_init(void)
 	init_events();
 }
 
+static int trace_kho_notifier(struct notifier_block *self,
+			      unsigned long cmd,
+			      void *v)
+{
+	const char compatible[] = "ftrace-v1";
+	void *fdt = v;
+	int err = 0;
+
+	switch (cmd) {
+	case KEXEC_KHO_ABORT:
+		if (trace_in_kho)
+			mutex_unlock(&trace_types_lock);
+		trace_in_kho = false;
+		return NOTIFY_DONE;
+	case KEXEC_KHO_DUMP:
+		/* Handled below */
+		break;
+	default:
+		return NOTIFY_BAD;
+	}
+
+	if (unlikely(tracing_disabled))
+		return NOTIFY_DONE;
+
+	err |= fdt_begin_node(fdt, "ftrace");
+	err |= fdt_property(fdt, "compatible", compatible, sizeof(compatible));
+	err |= fdt_end_node(fdt);
+
+	if (!err) {
+		/* Hold all future allocations */
+		mutex_lock(&trace_types_lock);
+		trace_in_kho = true;
+	}
+
+	return err ? NOTIFY_BAD : NOTIFY_DONE;
+}
+
+static struct notifier_block trace_kho_nb = {
+	.notifier_call = trace_kho_notifier,
+};
+
 void __init trace_init(void)
 {
 	trace_event_init();
 
 	if (boot_instance_index)
 		enable_instances();
+
+	if (IS_ENABLED(CONFIG_FTRACE_KHO))
+		register_kho_notifier(&trace_kho_nb);
 }
 
 __init static void clear_boot_tracer(void)
-- 
2.40.1




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