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From: Huang Yiwei <quic_hyiwei@quicinc.com>
To: <rostedt@goodmis.org>, <mhiramat@kernel.org>, <mark.rutland@arm.com>,
        <mcgrof@kernel.org>, <keescook@chromium.org>, <j.granados@samsung.com>,
        <mathieu.desnoyers@efficios.com>, <corbet@lwn.net>
CC: <linux-kernel@vger.kernel.org>, <linux-trace-kernel@vger.kernel.org>,
        <linux-fsdevel@vger.kernel.org>, <linux-doc@vger.kernel.org>,
        <quic_bjorande@quicinc.com>, <quic_tsoni@quicinc.com>,
        <quic_satyap@quicinc.com>, <quic_aiquny@quicinc.com>,
        <kernel@quicinc.com>, Huang Yiwei <quic_hyiwei@quicinc.com>,
        Ross Zwisler <zwisler@google.com>,
        Joel Fernandes <joel@joelfernandes.org>
Subject: [PATCH v3] tracing: Support to dump instance traces by ftrace_dump_on_oops
Date: Fri, 19 Jan 2024 16:08:24 +0800
Message-ID: <20240119080824.907101-1-quic_hyiwei@quicinc.com>
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Currently ftrace only dumps the global trace buffer on an OOPs. For
debugging a production usecase, instance trace will be helpful to
check specific problems since global trace buffer may be used for
other purposes.

This patch extend the ftrace_dump_on_oops parameter to dump a specific
trace instance:

  - ftrace_dump_on_oops=0: as before -- don't dump
  - ftrace_dump_on_oops[=1]: as before -- dump the global trace buffer
  on all CPUs
  - ftrace_dump_on_oops=2 or =orig_cpu: as before -- dump the global
  trace buffer on CPU that triggered the oops
  - ftrace_dump_on_oops=<instance_name>: new behavior -- dump the
  tracing instance matching <instance_name>

Also, the sysctl node can handle the input accordingly.

Cc: Ross Zwisler <zwisler@google.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Huang Yiwei <quic_hyiwei@quicinc.com>
---
Link: https://lore.kernel.org/linux-trace-kernel/20221209125310.450aee97@gandalf.local.home/

 .../admin-guide/kernel-parameters.txt         |  9 +--
 Documentation/admin-guide/sysctl/kernel.rst   | 11 ++--
 include/linux/ftrace.h                        |  4 +-
 include/linux/kernel.h                        |  1 +
 kernel/sysctl.c                               |  4 +-
 kernel/trace/trace.c                          | 64 ++++++++++++++-----
 kernel/trace/trace_selftest.c                 |  2 +-
 7 files changed, 65 insertions(+), 30 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a36cf8cc582c..b3aa533253f1 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1559,12 +1559,13 @@
 			The above will cause the "foo" tracing instance to trigger
 			a snapshot at the end of boot up.
 
-	ftrace_dump_on_oops[=orig_cpu]
+	ftrace_dump_on_oops[=orig_cpu | =<instance>]
 			[FTRACE] will dump the trace buffers on oops.
-			If no parameter is passed, ftrace will dump
-			buffers of all CPUs, but if you pass orig_cpu, it will
+			If no parameter is passed, ftrace will dump global
+			buffers of all CPUs, if you pass orig_cpu, it will
 			dump only the buffer of the CPU that triggered the
-			oops.
+			oops, or specific instance will be dumped if instance
+			name is passed.
 
 	ftrace_filter=[function-list]
 			[FTRACE] Limit the functions traced by the function
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 6584a1f9bfe3..ecf036b63c48 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -296,11 +296,12 @@ kernel panic). This will output the contents of the ftrace buffers to
 the console.  This is very useful for capturing traces that lead to
 crashes and outputting them to a serial console.
 
-= ===================================================
-0 Disabled (default).
-1 Dump buffers of all CPUs.
-2 Dump the buffer of the CPU that triggered the oops.
-= ===================================================
+=========== ===================================================
+0           Disabled (default).
+1           Dump buffers of all CPUs.
+2(orig_cpu) Dump the buffer of the CPU that triggered the oops.
+<instance>  Dump the specific instance buffer.
+=========== ===================================================
 
 
 ftrace_enabled, stack_tracer_enabled
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index e8921871ef9a..f20de4621ec1 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -1151,7 +1151,9 @@ static inline void unpause_graph_tracing(void) { }
 #ifdef CONFIG_TRACING
 enum ftrace_dump_mode;
 
-extern enum ftrace_dump_mode ftrace_dump_on_oops;
+#define MAX_TRACER_SIZE		100
+extern char ftrace_dump_on_oops[];
+extern enum ftrace_dump_mode get_ftrace_dump_mode(void);
 extern int tracepoint_printk;
 
 extern void disable_trace_on_warning(void);
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d9ad21058eed..de4a76036372 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -255,6 +255,7 @@ enum ftrace_dump_mode {
 	DUMP_NONE,
 	DUMP_ALL,
 	DUMP_ORIG,
+	DUMP_INSTANCE,
 };
 
 #ifdef CONFIG_TRACING
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 157f7ce2942d..81cc974913bb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1710,9 +1710,9 @@ static struct ctl_table kern_table[] = {
 	{
 		.procname	= "ftrace_dump_on_oops",
 		.data		= &ftrace_dump_on_oops,
-		.maxlen		= sizeof(int),
+		.maxlen		= MAX_TRACER_SIZE,
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dostring,
 	},
 	{
 		.procname	= "traceoff_on_warning",
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a0defe156b57..9a76a278e5c3 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -130,9 +130,10 @@ cpumask_var_t __read_mostly	tracing_buffer_mask;
  * /proc/sys/kernel/ftrace_dump_on_oops
  * Set 1 if you want to dump buffers of all CPUs
  * Set 2 if you want to dump the buffer of the CPU that triggered oops
+ * Set instance name if you want to dump the specific trace instance
  */
-
-enum ftrace_dump_mode ftrace_dump_on_oops;
+/* Set to string format zero to disable by default */
+char ftrace_dump_on_oops[MAX_TRACER_SIZE] = "0";
 
 /* When set, tracing will stop when a WARN*() is hit */
 int __disable_trace_on_warning;
@@ -178,7 +179,6 @@ static void ftrace_trace_userstack(struct trace_array *tr,
 				   struct trace_buffer *buffer,
 				   unsigned int trace_ctx);
 
-#define MAX_TRACER_SIZE		100
 static char bootup_tracer_buf[MAX_TRACER_SIZE] __initdata;
 static char *default_bootup_tracer;
 
@@ -201,19 +201,32 @@ static int __init set_cmdline_ftrace(char *str)
 }
 __setup("ftrace=", set_cmdline_ftrace);
 
+enum ftrace_dump_mode get_ftrace_dump_mode(void)
+{
+	if (!strcmp("0", ftrace_dump_on_oops))
+		return DUMP_NONE;
+	else if (!strcmp("1", ftrace_dump_on_oops))
+		return DUMP_ALL;
+	else if (!strcmp("orig_cpu", ftrace_dump_on_oops) ||
+			!strcmp("2", ftrace_dump_on_oops))
+		return DUMP_ORIG;
+	else
+		return DUMP_INSTANCE;
+}
+
 static int __init set_ftrace_dump_on_oops(char *str)
 {
-	if (*str++ != '=' || !*str || !strcmp("1", str)) {
-		ftrace_dump_on_oops = DUMP_ALL;
+	if (!*str) {
+		strscpy(ftrace_dump_on_oops, "1", MAX_TRACER_SIZE);
 		return 1;
 	}
 
-	if (!strcmp("orig_cpu", str) || !strcmp("2", str)) {
-		ftrace_dump_on_oops = DUMP_ORIG;
-                return 1;
-        }
+	if (*str++ == '=') {
+		strscpy(ftrace_dump_on_oops, str, MAX_TRACER_SIZE);
+		return 1;
+	}
 
-        return 0;
+	return 0;
 }
 __setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);
 
@@ -10085,14 +10098,16 @@ static struct notifier_block trace_die_notifier = {
 static int trace_die_panic_handler(struct notifier_block *self,
 				unsigned long ev, void *unused)
 {
-	if (!ftrace_dump_on_oops)
+	enum ftrace_dump_mode dump_mode = get_ftrace_dump_mode();
+
+	if (!dump_mode)
 		return NOTIFY_DONE;
 
 	/* The die notifier requires DIE_OOPS to trigger */
 	if (self == &trace_die_notifier && ev != DIE_OOPS)
 		return NOTIFY_DONE;
 
-	ftrace_dump(ftrace_dump_on_oops);
+	ftrace_dump(dump_mode);
 
 	return NOTIFY_DONE;
 }
@@ -10133,12 +10148,12 @@ trace_printk_seq(struct trace_seq *s)
 	trace_seq_init(s);
 }
 
-void trace_init_global_iter(struct trace_iterator *iter)
+static void trace_init_iter(struct trace_iterator *iter, struct trace_array *tr)
 {
-	iter->tr = &global_trace;
+	iter->tr = tr;
 	iter->trace = iter->tr->current_trace;
 	iter->cpu_file = RING_BUFFER_ALL_CPUS;
-	iter->array_buffer = &global_trace.array_buffer;
+	iter->array_buffer = &tr->array_buffer;
 
 	if (iter->trace && iter->trace->open)
 		iter->trace->open(iter);
@@ -10158,6 +10173,11 @@ void trace_init_global_iter(struct trace_iterator *iter)
 	iter->fmt_size = STATIC_FMT_BUF_SIZE;
 }
 
+void trace_init_global_iter(struct trace_iterator *iter)
+{
+	trace_init_iter(iter, &global_trace);
+}
+
 void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
 {
 	/* use static because iter can be a bit big for the stack */
@@ -10168,6 +10188,15 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
 	unsigned long flags;
 	int cnt = 0, cpu;
 
+	if (oops_dump_mode == DUMP_INSTANCE) {
+		tr = trace_array_find(ftrace_dump_on_oops);
+		if (!tr) {
+			printk(KERN_TRACE "Instance %s not found\n",
+				ftrace_dump_on_oops);
+			return;
+		}
+	}
+
 	/* Only allow one dump user at a time. */
 	if (atomic_inc_return(&dump_running) != 1) {
 		atomic_dec(&dump_running);
@@ -10182,12 +10211,12 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
 	 * If the user does a sysrq-z, then they can re-enable
 	 * tracing with echo 1 > tracing_on.
 	 */
-	tracing_off();
+	tracer_tracing_off(tr);
 
 	local_irq_save(flags);
 
 	/* Simulate the iterator */
-	trace_init_global_iter(&iter);
+	trace_init_iter(&iter, tr);
 
 	for_each_tracing_cpu(cpu) {
 		atomic_inc(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);
@@ -10200,6 +10229,7 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
 
 	switch (oops_dump_mode) {
 	case DUMP_ALL:
+	case DUMP_INSTANCE:
 		iter.cpu_file = RING_BUFFER_ALL_CPUS;
 		break;
 	case DUMP_ORIG:
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 529590499b1f..a9750a680324 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -768,7 +768,7 @@ static int trace_graph_entry_watchdog(struct ftrace_graph_ent *trace)
 	if (unlikely(++graph_hang_thresh > GRAPH_MAX_FUNC_TEST)) {
 		ftrace_graph_stop();
 		printk(KERN_WARNING "BUG: Function graph tracer hang!\n");
-		if (ftrace_dump_on_oops) {
+		if (get_ftrace_dump_mode()) {
 			ftrace_dump(DUMP_ALL);
 			/* ftrace_dump() disables tracing */
 			tracing_on();
-- 
2.25.1