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Date: Mon, 22 Jan 2024 14:56:45 +0100
From: Joel Granados <j.granados@samsung.com>
To: Huang Yiwei <quic_hyiwei@quicinc.com>
CC: <rostedt@goodmis.org>, <mhiramat@kernel.org>, <mark.rutland@arm.com>,
	<mcgrof@kernel.org>, <keescook@chromium.org>,
	<mathieu.desnoyers@efficios.com>, <corbet@lwn.net>,
	<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>,
	Ross Zwisler <zwisler@google.com>, Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH v3] tracing: Support to dump instance traces by
 ftrace_dump_on_oops
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	<20240119080824.907101-1-quic_hyiwei@quicinc.com>

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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.
>=20
> This patch extend the ftrace_dump_on_oops parameter to dump a specific
> trace instance:
>=20
>   - ftrace_dump_on_oops=3D0: as before -- don't dump
>   - ftrace_dump_on_oops[=3D1]: as before -- dump the global trace buffer
>   on all CPUs
>   - ftrace_dump_on_oops=3D2 or =3Dorig_cpu: as before -- dump the global
>   trace buffer on CPU that triggered the oops
>   - ftrace_dump_on_oops=3D<instance_name>: new behavior -- dump the
>   tracing instance matching <instance_name>
>=20
> Also, the sysctl node can handle the input accordingly.
>=20
> 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/
>=20
>  .../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(-)
>=20
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentat=
ion/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.
> =20
> -	ftrace_dump_on_oops[=3Dorig_cpu]
> +	ftrace_dump_on_oops[=3Dorig_cpu | =3D<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.
> =20
>  	ftrace_filter=3D[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.
> =20
> -=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D
> -0 Disabled (default).
> -1 Dump buffers of all CPUs.
> -2 Dump the buffer of the CPU that triggered the oops.
> -=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D
> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> +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.
> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> =20
> =20
>  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;
> =20
> -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;
> =20
>  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,
>  };
> =20
>  #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[] =3D {
>  	{
>  		.procname	=3D "ftrace_dump_on_oops",
>  		.data		=3D &ftrace_dump_on_oops,
> -		.maxlen		=3D sizeof(int),
> +		.maxlen		=3D MAX_TRACER_SIZE,
>  		.mode		=3D 0644,
> -		.proc_handler	=3D proc_dointvec,
> +		.proc_handler	=3D proc_dostring,
>  	},
>  	{
>  		.procname	=3D "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] =3D "0";
> =20
>  /* 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);
> =20
> -#define MAX_TRACER_SIZE		100
>  static char bootup_tracer_buf[MAX_TRACER_SIZE] __initdata;
>  static char *default_bootup_tracer;
> =20
> @@ -201,19 +201,32 @@ static int __init set_cmdline_ftrace(char *str)
>  }
>  __setup("ftrace=3D", set_cmdline_ftrace);
> =20
> +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++ !=3D '=3D' || !*str || !strcmp("1", str)) {
> -		ftrace_dump_on_oops =3D DUMP_ALL;
> +	if (!*str) {
> +		strscpy(ftrace_dump_on_oops, "1", MAX_TRACER_SIZE);
>  		return 1;
>  	}
> =20
> -	if (!strcmp("orig_cpu", str) || !strcmp("2", str)) {
> -		ftrace_dump_on_oops =3D DUMP_ORIG;
> -                return 1;
> -        }
> +	if (*str++ =3D=3D '=3D') {
> +		strscpy(ftrace_dump_on_oops, str, MAX_TRACER_SIZE);
> +		return 1;
> +	}
> =20
> -        return 0;
> +	return 0;
>  }
>  __setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);
> =20
> @@ -10085,14 +10098,16 @@ static struct notifier_block trace_die_notifier=
 =3D {
>  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 =3D get_ftrace_dump_mode();
> +
> +	if (!dump_mode)
>  		return NOTIFY_DONE;
> =20
>  	/* The die notifier requires DIE_OOPS to trigger */
>  	if (self =3D=3D &trace_die_notifier && ev !=3D DIE_OOPS)
>  		return NOTIFY_DONE;
> =20
> -	ftrace_dump(ftrace_dump_on_oops);
> +	ftrace_dump(dump_mode);
> =20
>  	return NOTIFY_DONE;
>  }
> @@ -10133,12 +10148,12 @@ trace_printk_seq(struct trace_seq *s)
>  	trace_seq_init(s);
>  }
> =20
> -void trace_init_global_iter(struct trace_iterator *iter)
> +static void trace_init_iter(struct trace_iterator *iter, struct trace_ar=
ray *tr)
>  {
> -	iter->tr =3D &global_trace;
> +	iter->tr =3D tr;
>  	iter->trace =3D iter->tr->current_trace;
>  	iter->cpu_file =3D RING_BUFFER_ALL_CPUS;
> -	iter->array_buffer =3D &global_trace.array_buffer;
> +	iter->array_buffer =3D &tr->array_buffer;
> =20
>  	if (iter->trace && iter->trace->open)
>  		iter->trace->open(iter);
> @@ -10158,6 +10173,11 @@ void trace_init_global_iter(struct trace_iterato=
r *iter)
>  	iter->fmt_size =3D STATIC_FMT_BUF_SIZE;
>  }
> =20
> +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 =3D 0, cpu;
> =20
> +	if (oops_dump_mode =3D=3D DUMP_INSTANCE) {
> +		tr =3D 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) !=3D 1) {
>  		atomic_dec(&dump_running);
> @@ -10182,12 +10211,12 @@ void ftrace_dump(enum ftrace_dump_mode oops_dum=
p_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);
> =20
>  	local_irq_save(flags);
> =20
>  	/* Simulate the iterator */
> -	trace_init_global_iter(&iter);
> +	trace_init_iter(&iter, tr);
> =20
>  	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)
> =20
>  	switch (oops_dump_mode) {
>  	case DUMP_ALL:
> +	case DUMP_INSTANCE:
>  		iter.cpu_file =3D 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_g=
raph_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();
> --=20
> 2.25.1
>=20

--=20

Joel Granados

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