[v5] tracing: Support to dump instance traces by ftrace_dump_on_oops

  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.

Cc: Ross Zwisler <zwisler@google.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Huang Yiwei <quic_hyiwei@quicinc.com>
---
 .../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(-)
  

On 2/23/2024 9:47 AM, Steven Rostedt wrote:
> On Thu, 8 Feb 2024 21:18:14 +0800
> Huang Yiwei <quic_hyiwei@quicinc.com> wrote:
> 
>> 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.
>>
>> Cc: Ross Zwisler <zwisler@google.com>
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>> Signed-off-by: Huang Yiwei <quic_hyiwei@quicinc.com>
> 
> This patch failed with the following warning:
> 
>    kernel/trace/trace.c:10029:6: warning: no previous prototype for ‘ftrace_dump_one’ [-Wmissing-prototypes]
> 
> -- Steve

My bad, will add the missing 'static' keyword in next patch.

Regards,
Huang Yiwei
  

On Thu, 8 Feb 2024 21:18:14 +0800
Huang Yiwei <quic_hyiwei@quicinc.com> wrote:

> 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],

Would you mean "ftrace_dump_on_oops,<instance1_name>" ?
As far as I can see, it doesn't work. Command line parser requires "="
for parameter value. Also, is there any reason to limit the parameter
to 2 or orig_cpu?

What about this syntax?

ftrace_dump_on_oops=<0|1|2|orig_cpu>[,<instance_name>[=<1|2|orig_cpu>][,...]

or

ftrace_dump_on_oops=instance_name[=<1|2|orig_cpu>][,...]

or

ftrace_dump_on_oops

e.g.
"ftrace_dump_on_oops=0,foo=orig_cpu" is equal to "ftrace_dump_on_oops=foo=orig_cpu"

Thank you,


>   <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.
> 
> Cc: Ross Zwisler <zwisler@google.com>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> Signed-off-by: Huang Yiwei <quic_hyiwei@quicinc.com>
> ---
>  .../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 2a7c6fd934e9..5622614d3035 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);
>  
> @@ -10243,14 +10259,14 @@ 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;
>  }
> @@ -10291,12 +10307,12 @@ 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);
> @@ -10316,22 +10332,19 @@ 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);
> +}
> +
> +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
> @@ -10340,12 +10353,12 @@ 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);
> @@ -10356,21 +10369,15 @@ 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()) {
> @@ -10412,15 +10419,84 @@ 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();
> -- 
> 2.25.1
>
  

On 2/27/2024 9:47 AM, Steven Rostedt wrote:
> On Thu, 8 Feb 2024 21:18:14 +0800
> Huang Yiwei <quic_hyiwei@quicinc.com> wrote:
> 
>> 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
> 
> So we need to add that the syntax is:
> 
>   ftrace_dump_on_oops[=[<0|1|2|orig_cpu>,][<instance_name>[=<1|2|orig_cpu>][,...]]
> 
Yeah, this is much more clear, will update the commit message and kernel 
docs in new patchset.
>>
>> 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>
>> ---
>>   .../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
> 
> I believe the above is incorrect. It should be:
> 
> 			ftrace_dump_on_oops=foo,bar=orig_cpu
> 
> And you can add here as well:
> 
>    ftrace_dump_on_oops[=[<0|1|2|orig_cpu>,][<instance_name>[=<1|2|orig_cpu>][,...]]
> 
> 
> Thanks,
> 
> --Steve
> 
The explanation is below, I think it's correct?
  - "ftrace_dump_on_oops," means global buffer on all CPUs
  - "foo," means foo instance on all CPUs
  - "bar=orig_cpu" means bar instance on CPU that triggered the oops.

I'm trying to make the example to cover more possibilities.

Regards,
Huang Yiwei
>> +
>> +			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]