Hello Masami-san,
On 02.02.24 07:04, Masami Hiramatsu (Google) wrote:
> On Thu, 1 Feb 2024 13:21:37 +0100
> Ahmad Fatoum <a.fat...@pengutronix.de> wrote:
>> For drivers that don't call dev_err_probe, I find myself sometimes doing
>> printf
>> debugging inside the probe function.
[snip]
>> I would like to replace this with the function graph tracer:
>>
>> - record the probe function, configured over kernel command line
>> (The device indefinitely deferring probe is printed to the console,
>> so I know what I am looking for on the next boot)
>>
>> - Dump the function graph trace
>>
>> - See if the last call before (non-devm) cleanup is getting a clock, a
>> GPIO,
>> a regulator or w/e.
>
> What kind of information you prints by the printk()?
Just littering around some:
pr_notice("%s:%d\n", __func__, __LINE__);
to find where the probe function exits.
> If the target (suspicious driver probe function) is obvious, you can use
> kprobe
> event and tp_printk. Or, even if you don't know, if you are sure which
> function
> is the starting/ending point, you can use bootconfig to record the specific
> part
> of execution in the ring buffer, and dump it as Steve said.
>
> In Documentation/trace/boottime-trace.rst, there is an example.
> -----
> With the trigger action and kprobes, you can trace function-graph while
> a function is called. For example, this will trace all function calls in
> the pci_proc_init()::
>
> ftrace {
> tracing_on = 0
> tracer = function_graph
> event.kprobes {
> start_event {
> probes = "pci_proc_init"
> actions = "traceon"
> }
> end_event {
> probes = "pci_proc_init%return"
> actions = "traceoff"
> }
> }
> }
I get comparable tracing with the kernel command line, but lacked a way to dump
it at boot-time. Sorry should have been clearer.
Grepping the kernel source for `ftrace_func_command' lets me think that
what I am after might be:
end_event {
actions = "traceoff", "dump"
}
I need to try it out. Do you happen to know if the equivalent is possible
without bootconfig?
Thank you!
Ahmad
> -----
>
> Thank you,
>
>>
>> For this to be maximally useful, I need to configure this not only at
>> boot-time,
>> but also dump the ftrace buffer at boot time. Probe deferral can hinder the
>> kernel from
>> calling init and providing a shell, where I could read
>> /sys/kernel/tracing/trace.
>>
>> I found following two mechanisms that looked relevant, but seem not to
>> do exactly what I want:
>>
>> - tp_printk: seems to be related to trace points only and not usable
>> for the function graph output
>>
>> - dump_on_oops: I don't get an Oops if probe deferral times out, but maybe
>> one could patch the kernel to check a oops_on_probe_deferral or
>> dump_on_probe_deferral
>> kernel command line parameter in deferred_probe_timeout_work_func()?
>>
>>
>> Is there existing support that I am missing? Any input on whether this
>> would be a welcome feature to have?
>>
>> Thanks!
>>
>> Cheers,
>> Ahmad
>>
>> --
>> Pengutronix e.K. | |
>> Steuerwalder Str. 21 | http://www.pengutronix.de/ |
>> 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
>> Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
>>
>
>
--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
