Message-ID: <20240122135645.danb777cc5e7i77z@localhost>
Date: Mon, 22 Jan 2024 14:56:45 +0100
From: Joel Granados <j.granados@...sung.com>
To: Huang Yiwei <quic_hyiwei@...cinc.com>
CC: <rostedt@...dmis.org>, <mhiramat@...nel.org>, <mark.rutland@....com>,
	<mcgrof@...nel.org>, <keescook@...omium.org>,
	<mathieu.desnoyers@...icios.com>, <corbet@....net>,
	<linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
	<linux-fsdevel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<quic_bjorande@...cinc.com>, <quic_tsoni@...cinc.com>,
	<quic_satyap@...cinc.com>, <quic_aiquny@...cinc.com>, <kernel@...cinc.com>,
	Ross Zwisler <zwisler@...gle.com>, Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v3] tracing: Support to dump instance traces by
 ftrace_dump_on_oops

On Fri, Jan 19, 2024 at 04:08:24PM +0800, Huang Yiwei 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
> 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@...gle.com>
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> Signed-off-by: Huang Yiwei <quic_hyiwei@...cinc.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))
Would using a strncmp be better in this case? And this question goes for
all the strcmp in the patch. Something like strncmp("0",
ftrace_dump_on_oops, 1); when they are equal, it would avoid 2
assignments and two comparisons. Also might avoid runaway comparisons if
the first string constant changes in the future.

Or maybe strncmp("0", ftrace_dump_on_oops, 2); if you want to check if
they are both null terminated.

> +		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
> 

-- 

Joel Granados

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