From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: Re: [PATCH RT] kernel/printk: Don't try to print from IRQ/NMI region Date: Fri, 27 May 2016 16:56:01 +0200 Message-ID: <20160527145601.GC24120@linutronix.de> References: <20160527135812.GB24120@linutronix.de> <20160527101251.0ae36e23@gandalf.local.home> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de To: Steven Rostedt Return-path: Received: from www.linutronix.de ([62.245.132.108]:47473 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754373AbcE0O4F convert rfc822-to-8bit (ORCPT ); Fri, 27 May 2016 10:56:05 -0400 Content-Disposition: inline In-Reply-To: <20160527101251.0ae36e23@gandalf.local.home> Sender: linux-rt-users-owner@vger.kernel.org List-ID: * Steven Rostedt | 2016-05-27 10:12:51 [-0400]: >On Fri, 27 May 2016 15:58:12 +0200 >Sebastian Andrzej Siewior wrote: > >> On -RT we try to acquire sleeping locks which might lead to warnings >> from lockdep or a warn_on() from spin_try_lock() (which is a rtmutex= on >> RT). >> We don't print in general from a IRQ off region so we should not try >> this via console_unblank() / bust_spinlocks() as well. >>=20 >> Signed-off-by: Sebastian Andrzej Siewior >> --- >> kernel/printk/printk.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >>=20 >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -1502,6 +1502,11 @@ static void call_console_drivers(int lev >> if (!console_drivers) >> return; >> =20 >> + if (IS_ENABLED(CONFIG_PREEMPT_RT_BASE)) { >> + if (in_irq() || in_nmi()) >> + return; >> + } >> + > >We use to have a patch where a console could flag itself as atomic. >That is, that it doesn't call any sleeping locks. What happened to tha= t. > >IIRC, the video console was one such console. Otherwise, we lose out o= n >backtraces in irq context. video, like VT? The call_console_drivers() does not check such a flag and I don't remember about removing something like that. I was actually thinking about adding such a flag=E2=80=A6 I remember you had something in your = tree to print from IRQ off regions via UART. We don't print from a context with interrupts disabled or even a preemp= t disabled region. In such cases we just wake_up_klogd() and print it later. The reason for the patch was the HW/SW lockup detector which comes with interrupts disabled or NMI context and gets to the console(s). Usually we defer everything until later except in this case. And I got busted later in the VT code (and the problem was that one sleeping while atomi= c warning which led to more stuff to be printed). Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-rt-user= s" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html