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From: Steven Rostedt <rostedt@goodmis.org>
To: paulmck@linux.vnet.ibm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.cz>, Jan Kara <jack@suse.cz>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Dave Anderson <anderson@redhat.com>,
	Jiri Kosina <jkosina@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Petr Mladek <pmladek@suse.cz>, Kay Sievers <kay@vrfy.org>
Subject: Re: [RFC PATCH 00/11] printk: safe printing in NMI context
Date: Wed, 18 Jun 2014 12:38:37 -0400	[thread overview]
Message-ID: <20140618123837.0073be7d@gandalf.local.home> (raw)
In-Reply-To: <20140618162117.GM4669@linux.vnet.ibm.com>

On Wed, 18 Jun 2014 09:21:17 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> On Wed, Jun 18, 2014 at 05:58:40AM -1000, Linus Torvalds wrote:
> > On Jun 18, 2014 4:36 AM, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > wrote:
> > >
> > > I could easily add an option to RCU to allow people to tell it not to
> > > use NMIs to dump the stack.
> > 
> > I don't think it should be an "option".
> > 
> > We should stop using nmi as if it was something "normal". It isn't. Code
> > running in nmi context should be special, and should be very very aware
> > that it is special. That goes way beyond "don't use printk". We seem to
> > have gone way way too far in using nmi context.
> > 
> > So we should get *rid* of code in nmi context rather than then complain
> > about printk being buggy.
> 
> OK, unconditional non-use of NMIs is even easier.  ;-)
> 
> Something like the following.
> 

I have found the RCU stalls extremely useful in debugging lockups. In
case this doesn't work as well, I'm willing to write up something that
could send NMIs to all CPUs that would write into the ftrace ring
buffer and when finished, the calling CPU can dump it out. No printk
from NMI context at all.

-- Steve

  reply	other threads:[~2014-06-18 16:38 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-05-09  9:10 [RFC PATCH 00/11] printk: safe printing in NMI context Petr Mladek
2014-05-09  9:10 ` [RFC PATCH 01/11] printk: rename struct printk_log to printk_msg Petr Mladek
2014-05-09  9:10 ` [RFC PATCH 02/11] printk: allow to handle more log buffers Petr Mladek
2014-05-09  9:10 ` [RFC PATCH 03/11] printk: rename "logbuf_lock" to "main_logbuf_lock" Petr Mladek
2014-05-09  9:10 ` [RFC PATCH 04/11] printk: add NMI ring and cont buffers Petr Mladek
2014-05-09  9:10 ` [RFC PATCH 05/11] printk: allow to modify NMI log buffer size using boot parameter Petr Mladek
2014-05-09  9:11 ` [RFC PATCH 06/11] printk: NMI safe printk Petr Mladek
2014-05-09  9:11 ` [RFC PATCH 07/11] printk: right ordering of the cont buffers from NMI context Petr Mladek
2014-05-09  9:11 ` [RFC PATCH 08/11] printk: try hard to print Oops message in " Petr Mladek
2014-05-09  9:11 ` [RFC PATCH 09/11] printk: merge and flush NMI buffer predictably via IRQ work Petr Mladek
2014-05-09  9:11 ` [RFC PATCH 10/11] printk: survive rotation of sequence numbers Petr Mladek
2014-05-09  9:11 ` [RFC PATCH 11/11] printk: avoid staling when merging NMI log buffer Petr Mladek
2014-05-28 22:02 ` [RFC PATCH 00/11] printk: safe printing in NMI context Jiri Kosina
2014-05-29  0:09   ` Frederic Weisbecker
2014-05-29  8:09     ` Jiri Kosina
2014-06-10 16:46       ` Frederic Weisbecker
2014-06-10 16:57         ` Linus Torvalds
2014-06-10 17:32           ` Jiri Kosina
2014-06-11  9:01             ` Petr Mládek
2014-06-18 11:03           ` Jiri Kosina
2014-06-18 14:36             ` Paul E. McKenney
2014-06-18 14:41               ` Jiri Kosina
2014-06-18 14:44                 ` Paul E. McKenney
2014-06-18 14:53                   ` Jiri Kosina
2014-06-18 15:07                     ` Paul E. McKenney
     [not found]               ` <CA+55aFwPgDC6gSEPfu3i-pA4f0ZbsTSvykxzX4sXMeLbdXuKrw@mail.gmail.com>
2014-06-18 16:21                 ` Paul E. McKenney
2014-06-18 16:38                   ` Steven Rostedt [this message]
2014-06-18 16:43                     ` Paul E. McKenney
2014-06-18 20:36                   ` Jiri Kosina
2014-06-18 21:07                     ` Paul E. McKenney
2014-06-18 21:12                       ` Jiri Kosina
2014-06-18 21:20                         ` Paul E. McKenney
2014-06-18 21:32                           ` Jiri Kosina
2014-06-18 21:37                             ` Paul E. McKenney
2014-06-18 23:20                         ` Steven Rostedt
2014-05-30  8:13     ` Jan Kara
2014-05-30 10:10       ` Jiri Kosina
2014-06-10 16:49       ` Frederic Weisbecker
2014-06-12 11:50     ` Petr Mládek

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