From: Nicolas Boichat <drinkcat@chromium.org>
To: David Laight <David.Laight@aculab.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Sakari Ailus <sakari.ailus@linux.intel.com>,
"devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
lkml <linux-kernel@vger.kernel.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v4 3/3] media: atomisp: Only use trace_printk if allowed
Date: Fri, 21 Aug 2020 20:37:15 +0800 [thread overview]
Message-ID: <CANMq1KCc-KObgJTe0vWXGHcsffMD=41VMe=GjtsKG0iobJES0Q@mail.gmail.com> (raw)
In-Reply-To: <6c5249afad274ce49e643d9b05706e3a@AcuMS.aculab.com>
On Fri, Aug 21, 2020 at 8:18 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Nicolas Boichat
> > Sent: 21 August 2020 13:07
> ...
> > > You might also want a #define that can set temporarily
> > > to enable traces in a specific file/module even though
> > > CONFIG_TRACE=n.
> >
> > I don't understand how traces are supposed to work with CONFIG_TRACE=n?
>
> Probably because I meant something different :-)
>
> You want the kernel built so that there are no (expanded)
> calls to trace_printf() but with support for modules that
> contain them.
>
> Then I can load a module into a distro kernel that
> contains trace_printf() calls for debug testing.
Gotcha. I think it already works this way ,-)
So if you have CONFIG_TRACE=y, but no trace_printk in your
vmlinux/kernel, no memory is used, and no warning splat
(https://elixir.bootlin.com/linux/v5.8/source/kernel/trace/trace.c#L3160)
is displayed. But then when you load a module with trace_printk, the
buffers are allocated and the warning splat is printed.
The magic is here:
https://elixir.bootlin.com/linux/v5.8/source/kernel/trace/trace_printk.c#L53
My option wouldn't really change that. I mean, if you have
CONFIG_TRACING_ALLOW_PRINTK=n when you compile your module, it'd fail
at build time, but if you set it to =y, your module could happily
build and load (with the big warning splat), no matter how you built
your kernel (I mean, you still need CONFIG_TRACE=y, but
CONFIG_TRACING_ALLOW_PRINTK doesn't matter).
> Which is why I was suggesting a config option that
> only rand-config builds would ever set that would
> cause the calls to generate compile-time errors.
I think I already answered that one above. We'd want that config
option enabled on Chrome OS and we're not a rand-config build (I mean,
we're a very carefully selected random config ,-P).
Thanks,
>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-08-21 12:37 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-20 9:14 [PATCH v4 1/3, RESEND] media: camss: vfe: Use trace_printk for debugging only Nicolas Boichat
2020-08-20 9:14 ` [PATCH v4 3/3] media: atomisp: Only use trace_printk if allowed Nicolas Boichat
2020-08-20 14:23 ` Steven Rostedt
2020-08-21 0:13 ` Nicolas Boichat
2020-08-21 0:36 ` Steven Rostedt
2020-08-21 1:39 ` Nicolas Boichat
2020-08-21 1:57 ` Steven Rostedt
2020-08-21 2:36 ` Joe Perches
2020-08-21 2:42 ` Nicolas Boichat
2020-08-21 2:49 ` Joe Perches
2020-08-21 3:04 ` Steven Rostedt
2020-08-21 3:08 ` Steven Rostedt
2020-08-21 2:44 ` Steven Rostedt
2020-08-21 2:39 ` Nicolas Boichat
2020-08-21 3:01 ` Steven Rostedt
2020-08-21 12:19 ` Nicolas Boichat
2020-08-21 8:48 ` David Laight
2020-08-21 10:27 ` Nicolas Boichat
2020-08-21 11:32 ` David Laight
2020-08-21 12:07 ` Nicolas Boichat
2020-08-21 12:18 ` David Laight
2020-08-21 12:37 ` Nicolas Boichat [this message]
2020-08-20 14:21 ` [PATCH v4 1/3, RESEND] media: camss: vfe: Use trace_printk for debugging only Steven Rostedt
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