Re: [PATCH v3] tracing: Support to dump instance traces by ftrace_dump_on_oops

From: Joel Granados
Date: Mon Jan 22 2024 - 08:57:05 EST

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@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/20221209125310.450aee97@xxxxxxxxxxxxxxxxxx/
>
> .../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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