linux-kernel - Re: [PATCH V2] dynamic_debug: Add an option to enable dynamic debug for modules only

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Message-ID: <20200518095026.GL7340@linux-b0ei>
Date:   Mon, 18 May 2020 11:50:26 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Orson Zhai <orsonzhai@...il.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Orson Zhai <orson.unisoc@...il.com>,
        Jason Baron <jbaron@...mai.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Orson Zhai <orson.zhai@...soc.com>
Subject: Re: [PATCH V2] dynamic_debug: Add an option to enable dynamic debug
 for modules only

On Sat 2020-05-16 11:55:04, Orson Zhai wrote:
> On Fri, May 15, 2020 at 5:55 PM Petr Mladek <pmladek@...e.com> wrote:
> >
> > On Thu 2020-04-23 00:02:48, Orson Zhai wrote:
> > > On Wed, Apr 22, 2020 at 10:25 PM Leon Romanovsky <leon@...nel.org> wrote:
> > > >
> > > > On Wed, Apr 22, 2020 at 09:06:08PM +0800, Orson Zhai wrote:
> > > > > On Tue, Apr 21, 2020 at 3:10 AM Leon Romanovsky <leon@...nel.org> wrote:
> > > > > My motivation came from the concept of GKI (Generic Kernel Image) in Android.
> > > > > Google will release a common kernel image (binary) to all of the Android system
> > > > > vendors in the world instead of letting them to build their owns as before.
> > > > > Every SoC vendor's device drivers will be provided in kernel modules only.
> > > > > By my patch, the driver owners could debug their modules in field (say
> > > > > production releases)
> > > > > without having to enable dynamic debug for the whole GKI.
> > > >
> > > > Will Google release that binary with CONFIG_DYNAMIC_DEBUG_CORE disabled?
> > > >
> > > In Google's plan, there will be only one GKI (no debug version) for
> > > one Android version per kernel version per year.
> >
> > Are there plans to use modules with debug messages enabled on production
> > systems?
> 
> Yes, but in a managed way. They are not being enabled directly to log buffer.
> Users / FAEs (Field Application Engineer) might control to open or
> close every single one on-the-fly.

I see.

> > IMHO, the debug messages are primary needed during development and
> > when fixing bugs. I am sure that developers will want to enable many
> > more features that will help with debugging and which will be disabled
> > on production systems.
> 
> I agree with you in general speaking.
> For real production build we usually keep a few critical debugging
> methods in case of some
> potential bugs which are extremely hard to be found in production test.
> Dynamic debug is one of these methods.
> I assume it is widely used for maintenance to PC or server because I
> can find it is enabled in some
> popular Linux distribution configs.

Fair enough.

Feel free to add:

Acked-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr