Re: [PATCH v4] tracing: Support to dump instance traces by ftrace_dump_on_oops
From: Joel Fernandes
Date: Wed Feb 07 2024 - 05:25:32 EST
On 2/6/2024 4:46 AM, 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
> 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@xxxxxxxxxx>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Huang Yiwei <quic_hyiwei@xxxxxxxxxxx>
> ---
> Link: https://lore.kernel.org/linux-trace-kernel/20240119080824.907101-1-quic_hyiwei@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..f4c05a43b561 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_opps[=2(orig_cpu) | =<instance>][,<instance> |
You introduced a typo to 'oops' here.
> + ,<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_opps=foo=orig_cpu
> +
> + The above will dump only the buffer of "foo" instance
> + on CPU that triggered the oops.
> +
> + ftrace_dump_on_opps,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);
DUMP_PARAM and ftrace_dump_by_param() is a bit of a misnomer, because it
optionally also dumps the original buffer, not just the instances. That's
probably OK though.
FWIW:
Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Btw, hopefully the "trace off on warning" and related boot parameters also apply
to instances, I haven't personally checked but I often couple those with the
dump-on-oops ones.
Thanks.