linux-kernel - Re: [PATCH v5] tracing: Support to dump instance traces by ftrace_dump_on

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Message-ID: <20240226204757.1a968a10@gandalf.local.home>
Date: Mon, 26 Feb 2024 20:47:57 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Huang Yiwei <quic_hyiwei@...cinc.com>
Cc: <mhiramat@...nel.org>, <mark.rutland@....com>, <mcgrof@...nel.org>,
 <keescook@...omium.org>, <j.granados@...sung.com>,
 <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 v5] tracing: Support to dump instance traces by
 ftrace_dump_on_oops

On Thu, 8 Feb 2024 21:18:14 +0800
Huang Yiwei <quic_hyiwei@...cinc.com> 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

So we need to add that the syntax is:

 ftrace_dump_on_oops[=[<0|1|2|orig_cpu>,][<instance_name>[=<1|2|orig_cpu>][,...]]

> 
> 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>
> ---
>  .../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..3d6ea8e80c2f 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_oops[=2(orig_cpu) | =<instance>][,<instance> |
> +			  ,<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_oops=foo=orig_cpu
> +
> +			The above will dump only the buffer of "foo" instance
> +			on CPU that triggered the oops.
> +
> +			ftrace_dump_on_oops,foo,bar=orig_cpu

I believe the above is incorrect. It should be:

			ftrace_dump_on_oops=foo,bar=orig_cpu

And you can add here as well:

  ftrace_dump_on_oops[=[<0|1|2|orig_cpu>,][<instance_name>[=<1|2|orig_cpu>][,...]]


Thanks,

--Steve

> +
> +			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]