linux-kernel - Re: printk: Add process name information to printk() output.

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Message-ID: <20200904103445.GA2693206@kroah.com>
Date:   Fri, 4 Sep 2020 12:34:45 +0200
From:   'Greg KH' <gregkh@...uxfoundation.org>
To:     ��â�� <changki.kim@...sung.com>
Cc:     pmladek@...e.com, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, john.ogness@...utronix.de,
        masahiroy@...nel.org, rd.dunlap@...il.com, krzk@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: printk: Add process name information to printk() output.

On Fri, Sep 04, 2020 at 06:31:13PM +0900, ��â�� wrote:
> > On Fri, Sep 04, 2020 at 05:24:38PM +0900, Changki Kim wrote:
> > > Printk() meesages are the most basic and useful debug method.
> > > However, additional information needs in multi-processor.
> > > If we add messages with processor id and process name, we can find a
> > > problem only with messages when the problem occurs with H/W IP or CPU.
> > > This is very useful in narrowing down the scope of the problems.
> > >
> > > Therefore, instead of trying to help buffering, let's try to help
> > > reconstructing messages by saving caller information as of calling
> > > log_store() and adding it as "[$processor_id: $process_name:
> > $thread_id]"
> > > upon printing to consoles.
> > >
> > > Some examples for console output:
> > >
> > >   [    0.059580] [0:      swapper/0:    1] CPU: All CPU(s) started at
> EL1i
> > >   [    2.153157] [5:           init:    1] migov: complete to probe
> migov
> > >   [    7.441317] [4:           init:    1] NET: Registered protocol
> family 39
> > >   [   22.793389] [5:  kworker/u16:1:  184] SMP: stopping secondary CPUs
> > >
> > > Signed-off-by: Changki Kim <changki.kim@...sung.com>
> > > ---
> > >  kernel/printk/printk.c            | 20 ++++++++++++++++++--
> > >  kernel/printk/printk_ringbuffer.h |  7 +++++++
> > >  lib/Kconfig.debug                 | 16 ++++++++++++++++
> > >  3 files changed, 41 insertions(+), 2 deletions(-)
> > 
> > Isn't the CPU number already present if you want it today?  Why add it
> > again?
> > 
> > thanks,
> > 
> > greg k-h
> 
> CPU number isn't present now. If I enabled PRINTK_CALLER,
> then it is present cpu id or thread id.

Great, that should give you what you need here, right?

> The config isn't always present cpu id.

What do you mean?

> We need cpu id each each message.

Why each message?  What does that provide you?

And if PRINTK_CALLER does not work properly, please fix it.  I don't see
how it would not work any different from your patch, you shouldn't
duplicate things.

thanks,

greg k-h