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Message-ID: <447F74DC.5030302@gmail.com>
Date: Fri, 02 Jun 2006 07:14:36 +0800
From: "Antonino A. Daplas" <adaplas@gmail.com>
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To: Jon Smirl <jonsmirl@gmail.com>
CC: "D. Hazelton" <dhazelton@enter.net>, David Lang <dlang@digitalinsight.com>,
       Ondrej Zajicek <santiago@mail.cz>, Dave Airlie <airlied@gmail.com>,
       Pavel Machek <pavel@ucw.cz>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Kyle Moffett <mrmacman_g4@mac.com>,
       Manu Abraham <abraham.manu@gmail.com>, linux cbon <linuxcbon@yahoo.fr>,
       Helge Hafting <helge.hafting@aitel.hist.no>, Valdis.Kletnieks@vt.edu,
       linux-kernel@vger.kernel.org
Subject: Re: OpenGL-based framebuffer concepts
References: <20060519224056.37429.qmail@web26611.mail.ukl.yahoo.com>	 <9e4733910606010959o4f11d7cfp2d280c6f2019cccf@mail.gmail.com>	 <Pine.LNX.4.63.0606010758380.3827@qynat.qvtvafvgr.pbz>	 <200606011603.57421.dhazelton@enter.net>	 <9e4733910606011335q5791997drc02d23f398a2acf5@mail.gmail.com>	 <447F56A0.8030408@gmail.com>	 <9e4733910606011423u75fa076hce22547c28c0a987@mail.gmail.com>	 <447F5CB3.7000107@gmail.com> <9e4733910606011448x32246dfcy2a2d448e238bdab3@mail.gmail.com>
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Jon Smirl wrote:
> On 6/1/06, Antonino A. Daplas <adaplas@gmail.com> wrote:
>> Jon Smirl wrote:
>> > On 6/1/06, Antonino A. Daplas <adaplas@gmail.com> wrote:
>> >> Jon Smirl wrote:
>> >> > On 6/1/06, D. Hazelton <dhazelton@enter.net> wrote:
>> >> >
>> >>
>> >> Console writes are done with the console semaphore held. printk
>> will also
>> >> just write to the log buffer and defer the actual console printing
>> >> for later, by the next or current process that will grab the
>> semaphore.
>> >
>> > That was my original position too. But Alan Cox has drilled it into me
>> > that this is not acceptable for printks in interrupt context, they
>> > need to print there and not be deferred.
>> >
>>
>> Just to clarify, it's not my position, that's how the current printk code
>> works.
> 
> I haven't looked at the code, but if there is just normal console
> running and nothing like X is around, doesn't the console system
> always have the semaphore? If it always has the semaphore then
> interupt context printk's aren't blocked.
> 
> I think that interrupt context printk's work today, I have definitely
> seen one printk get inserted into the middle of another on my console.
> How else could you achieve that?
> 

foreground calls acquire_console_sem()
foreground process does a printk, printk writes to log buffer
interrupt-> does a printk -> message inserted to log buffer
foreground process calls release_console_sem
release_console_sem() dumps log buffer contents to console driver

Tony