From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Nikita V. Youshchenko" Subject: Re: PREEMPT_RT (2.6.33-rt17) disabled printk-to-console after console_init Date: Thu, 20 May 2010 14:23:07 +0400 Message-ID: <201005201423.09075@zigzag.lvk.cs.msu.su> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Sujit K M , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org To: Thomas Gleixner Return-path: Received: from gate.lvk.cs.msu.su ([158.250.17.1]:42529 "EHLO mail.lvk.cs.msu.su" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751571Ab0ETKXM (ORCPT ); Thu, 20 May 2010 06:23:12 -0400 In-Reply-To: Content-Disposition: inline Sender: linux-rt-users-owner@vger.kernel.org List-ID: > > >>> Well, obviously it's unsafe if you remove safety checks. And if > > >>> you care to look at the changelog of kernel/printk.c you'll find > > >>> out why. > > >> > > >> Hmm... did a quick look and could not find anything related there. > > >> Could you please give a pointer? > > Gah, yes. The changelog of the commit is not really helpful. Let me > explain: > > The console drivers might take locks, which are converted to "sleeping > locks" in preempt-rt. As a result we cannot call into those drivers > from atomic contexts. And that's what the checks in the printk code > prevent. I've already understood that when looking at that code some weeks ago. Still questions: 1) why does that prevent klogd from working? 2) why does print not pass to non-CON_ATOMIC even if called from non-atomic context? 3) I believe that 8250 serial driver is aware of preempt-rt. Could you please comment on my "2.6.33.2-rt13: RFC: fix serial console" post to linux-rt-users list (http://eeek.borgchat.net/lists/linux-rt-users/msg05569.html) Nikita