linux-kernel - Re: [TIP,BISECTED] Negative nice values have become big positive numbers

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Message-ID: <20090309084132.GA5914@nowhere>
Date:	Mon, 9 Mar 2009 09:41:34 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Sitsofe Wheeler <sitsofe@...oo.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [TIP,BISECTED] Negative nice values have become big positive
	numbers

On Mon, Mar 09, 2009 at 08:08:24AM +0100, Ingo Molnar wrote:
> 
> * Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Sun, 8 Mar 2009, Sitsofe Wheeler wrote:
> > 
> > > (Forgot to cc lkml. Resending...)
> > > 
> > > Formally negative nice values have started become very big in positive
> > > integers in -tip kernels:
> > > 
> > >     2 root      15 2147483647     0    0    0 S  0.0  0.0   0:00.00 kthreadd    
> > 
> > Is this the output of top?
> 
> seems so.
> 
> > > I've just finished bisecting down to this commit:
> > > 
> > > commit 1427cdf0592368bdec57276edaf714040ee8744f
> > > Author: Lai Jiangshan <laijs@...fujitsu.com>
> > > Date:   Fri Mar 6 17:21:47 2009 +0100
> > 
> > $ git show 1427cdf0592368bdec57276edaf714040ee8744f  | diffstat
> >  include/linux/ftrace.h       |    3 +
> >  kernel/trace/Kconfig         |    6 ++
> >  kernel/trace/Makefile        |    1 
> >  kernel/trace/trace.c         |   56 +++++++++++++++++++++++++++
> >  kernel/trace/trace.h         |   12 +++++
> >  kernel/trace/trace_bprintk.c |   87 
> > +++++++++++++++++++++++++++++++++++++++++++
> >  kernel/trace/trace_output.c  |   75 +++++++++++++++++++++++++++++++++++++
> >  7 files changed, 240 insertions(+)
> > 
> > I find it hard to believe that this would cause normal nice 
> > values to be messed up. The only file that could could come 
> > close to messing with nice values in top is ftrace.h:
> 
> Correct - maybe it's these two nearby commits that cause the 
> problems:
> 
>  fef20d9: vsprintf: unify the format decoding layer for its 3 users
>  4370aa4: vsprintf: add binary printf
> 
> they do affect generic code. If we broke vsnprintf (which the 
> nice value output code uses) then that might be a plausible 
> explanation.
> 
> 	Ingo


Thanks for this report Sitsofe. I have some ideas about the origin of this bug.
Anyway I'm in the middle of moving to another town. There are very good chances
that I send a fix tomorrow but not today.

Thanks.

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