[for-next][PATCH 1/8] tracing: Support to dump instance traces by ftrace_dump_on_oops

From: Steven Rostedt
Date: Thu Mar 14 2024 - 10:21:44 EST

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From: Huang Yiwei <quic_hyiwei@xxxxxxxxxxx>

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
or multiple trace instances:

- 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>
- ftrace_dump_on_oops[=2/orig_cpu],<instance1_name>[=2/orig_cpu],
<instrance2_name>[=2/orig_cpu]: new behavior -- dump the global trace
buffer and multiple instance buffer on all CPUs, or only dump on CPU
that triggered the oops if =2 or =orig_cpu is given

Also, the sysctl node can handle the input accordingly.

Link: https://lore.kernel.org/linux-trace-kernel/20240223083126.1817731-1-quic_hyiwei@xxxxxxxxxxx

Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
Cc: <mhiramat@xxxxxxxxxx>
Cc: <mark.rutland@xxxxxxx>
Cc: <mcgrof@xxxxxxxxxx>
Cc: <keescook@xxxxxxxxxxxx>
Cc: <j.granados@xxxxxxxxxxx>
Cc: <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: <corbet@xxxxxxx>
Signed-off-by: Huang Yiwei <quic_hyiwei@xxxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
.../admin-guide/kernel-parameters.txt | 26 ++-
Documentation/admin-guide/sysctl/kernel.rst | 30 +++-
include/linux/ftrace.h | 4 +-
include/linux/kernel.h | 1 +
kernel/sysctl.c | 4 +-
kernel/trace/trace.c | 156 +++++++++++++-----
kernel/trace/trace_selftest.c | 2 +-
7 files changed, 168 insertions(+), 55 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 31b3a25680d0..3d6ea8e80c2f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1561,12 +1561,28 @@
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[=2(orig_cpu) | =<instance>][,<instance> |
+ ,<instance>=2(orig_cpu)]
[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
- dump only the buffer of the CPU that triggered the
- oops.
+ If no parameter is passed, ftrace will dump global
+ buffers of all CPUs, if you pass 2 or orig_cpu, it
+ will dump only the buffer of the CPU that triggered
+ the oops, or the specific instance will be dumped if
+ its name is passed. Multiple instance dump is also
+ supported, and instances are separated by commas. Each
+ instance supports only dump on CPU that triggered the
+ oops by passing 2 or orig_cpu to it.
+
+ ftrace_dump_on_oops=foo=orig_cpu
+
+ The above will dump only the buffer of "foo" instance
+ on CPU that triggered the oops.
+
+ ftrace_dump_on_oops,foo,bar=orig_cpu
+
+ The above will dump global buffer on all CPUs, the
+ buffer of "foo" instance on all CPUs and the buffer
+ of "bar" instance on CPU that triggered the oops.

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..ea8e5f152edc 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -296,12 +296,30 @@ 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 on all CPUs.
+<instance>=2(orig_cpu) Dump the specific instance buffer on the CPU
+ that triggered the oops.
+======================= ===========================================
+
+Multiple instance dump is also supported, and instances are separated
+by commas. If global buffer also needs to be dumped, please specify
+the dump mode (1/2/orig_cpu) first for global buffer.
+
+So for example to dump "foo" and "bar" instance buffer on all CPUs,
+user can::
+
+ echo "foo,bar" > /proc/sys/kernel/ftrace_dump_on_oops
+
+To dump global buffer and "foo" instance buffer on all
+CPUs along with the "bar" instance buffer on CPU that triggered the
+oops, user can::
+
+ echo "1,foo,bar=2" > /proc/sys/kernel/ftrace_dump_on_oops

ftrace_enabled, stack_tracer_enabled
====================================
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index e8921871ef9a..54d53f345d14 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 int ftrace_dump_on_oops_enabled(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..b142a4f41d34 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_PARAM,
};

#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 1bcfbc21fb3e..ff0b0a999171 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -130,9 +130,12 @@ 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
+ * Multiple instance dump is also supported, and instances are seperated
+ * by commas.
*/
-
-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 +181,6 @@ 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 +203,33 @@ static int __init set_cmdline_ftrace(char *str)
}
__setup("ftrace=", set_cmdline_ftrace);

+int ftrace_dump_on_oops_enabled(void)
+{
+ if (!strcmp("0", ftrace_dump_on_oops))
+ return 0;
+ else
+ return 1;
+}
+
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, "1", MAX_TRACER_SIZE);
+ strscpy(ftrace_dump_on_oops + 1, str, MAX_TRACER_SIZE - 1);
+ 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);

@@ -9932,14 +9948,14 @@ 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)
+ if (!ftrace_dump_on_oops_enabled())
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_PARAM);

return NOTIFY_DONE;
}
@@ -9980,12 +9996,12 @@ 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);
@@ -10005,22 +10021,19 @@ void trace_init_global_iter(struct trace_iterator *iter)
iter->fmt_size = STATIC_FMT_BUF_SIZE;
}

-void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
+void trace_init_global_iter(struct trace_iterator *iter)
+{
+ trace_init_iter(iter, &global_trace);
+}
+
+static void ftrace_dump_one(struct trace_array *tr, enum ftrace_dump_mode dump_mode)
{
/* use static because iter can be a bit big for the stack */
static struct trace_iterator iter;
- static atomic_t dump_running;
- struct trace_array *tr = &global_trace;
unsigned int old_userobj;
unsigned long flags;
int cnt = 0, cpu;

- /* Only allow one dump user at a time. */
- if (atomic_inc_return(&dump_running) != 1) {
- atomic_dec(&dump_running);
- return;
- }
-
/*
* Always turn off tracing when we dump.
* We don't need to show trace output of what happens
@@ -10029,12 +10042,12 @@ 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);
@@ -10045,21 +10058,15 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
/* don't look at user memory in panic mode */
tr->trace_flags &= ~TRACE_ITER_SYM_USEROBJ;

- switch (oops_dump_mode) {
- case DUMP_ALL:
- iter.cpu_file = RING_BUFFER_ALL_CPUS;
- break;
- case DUMP_ORIG:
+ if (dump_mode == DUMP_ORIG)
iter.cpu_file = raw_smp_processor_id();
- break;
- case DUMP_NONE:
- goto out_enable;
- default:
- printk(KERN_TRACE "Bad dumping mode, switching to all CPUs dump\n");
+ else
iter.cpu_file = RING_BUFFER_ALL_CPUS;
- }

- printk(KERN_TRACE "Dumping ftrace buffer:\n");
+ if (tr == &global_trace)
+ printk(KERN_TRACE "Dumping ftrace buffer:\n");
+ else
+ printk(KERN_TRACE "Dumping ftrace instance %s buffer:\n", tr->name);

/* Did function tracer already get disabled? */
if (ftrace_is_dead()) {
@@ -10101,15 +10108,84 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
else
printk(KERN_TRACE "---------------------------------\n");

- out_enable:
tr->trace_flags |= old_userobj;

for_each_tracing_cpu(cpu) {
atomic_dec(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);
}
- atomic_dec(&dump_running);
local_irq_restore(flags);
}
+
+static void ftrace_dump_by_param(void)
+{
+ bool first_param = true;
+ char dump_param[MAX_TRACER_SIZE];
+ char *buf, *token, *inst_name;
+ struct trace_array *tr;
+
+ strscpy(dump_param, ftrace_dump_on_oops, MAX_TRACER_SIZE);
+ buf = dump_param;
+
+ while ((token = strsep(&buf, ",")) != NULL) {
+ if (first_param) {
+ first_param = false;
+ if (!strcmp("0", token))
+ continue;
+ else if (!strcmp("1", token)) {
+ ftrace_dump_one(&global_trace, DUMP_ALL);
+ continue;
+ }
+ else if (!strcmp("2", token) ||
+ !strcmp("orig_cpu", token)) {
+ ftrace_dump_one(&global_trace, DUMP_ORIG);
+ continue;
+ }
+ }
+
+ inst_name = strsep(&token, "=");
+ tr = trace_array_find(inst_name);
+ if (!tr) {
+ printk(KERN_TRACE "Instance %s not found\n", inst_name);
+ continue;
+ }
+
+ if (token && (!strcmp("2", token) ||
+ !strcmp("orig_cpu", token)))
+ ftrace_dump_one(tr, DUMP_ORIG);
+ else
+ ftrace_dump_one(tr, DUMP_ALL);
+ }
+}
+
+void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
+{
+ static atomic_t dump_running;
+
+ /* Only allow one dump user at a time. */
+ if (atomic_inc_return(&dump_running) != 1) {
+ atomic_dec(&dump_running);
+ return;
+ }
+
+ switch (oops_dump_mode) {
+ case DUMP_ALL:
+ ftrace_dump_one(&global_trace, DUMP_ALL);
+ break;
+ case DUMP_ORIG:
+ ftrace_dump_one(&global_trace, DUMP_ORIG);
+ break;
+ case DUMP_PARAM:
+ ftrace_dump_by_param();
+ break;
+ case DUMP_NONE:
+ break;
+ default:
+ printk(KERN_TRACE "Bad dumping mode, switching to all CPUs dump\n");
+ ftrace_dump_one(&global_trace, DUMP_ALL);
+ }
+
+ atomic_dec(&dump_running);
+}
EXPORT_SYMBOL_GPL(ftrace_dump);

#define WRITE_BUFSIZE 4096
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 529590499b1f..e9c5058a8efd 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 (ftrace_dump_on_oops_enabled()) {
ftrace_dump(DUMP_ALL);
/* ftrace_dump() disables tracing */
tracing_on();
--
2.43.0

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