linux-kernel - Re: oprofile BUG() in current kernel.

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Date:	Tue, 13 May 2008 11:01:11 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	arges@...ux.vnet.ibm.com, "Maynard Johnson" <maynardj@...ibm.com>,
	"Gianni Tedesco" <gxt@...nott.ac.uk>, linux-kernel@...r.kernel.org,
	oprofile-list@...ts.sourceforge.net, "Mike Travis" <travis@....com>
Subject: Re: oprofile BUG() in current kernel.

On Tue, May 13, 2008 at 10:40 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 12 May 2008 11:38:03 -0500 Chris J Arges <arges@...ux.vnet.ibm.com> wrote:
>  > > >> Does reverting 608dfddd845da5ab6accef70154c8910529699f7 fix it for you too?
>  > > >>
>  > > Has this fix been officially reverted?
>  >
>
> > Let me know if this change is going to be reverted, as I have a patch
>  > ready to support cpu hotplug for oprofile based on code post
>  > DEFINE_PER_CPU patch.
>
>  Please don't top-post.  I repaired it so that I could reply sensibly.
>
>  In trying to reprocude this on a uniprocessor machine, it seems that
>  someone broke oprofile:
>
>  /usr/bin/opcontrol: line 911: /dev/oprofile/0/enabled: No such file or directory
>  /usr/bin/opcontrol: line 911: /dev/oprofile/0/event: No such file or directory
>  /usr/bin/opcontrol: line 911: /dev/oprofile/0/count: No such file or directory
>  /usr/bin/opcontrol: line 911: /dev/oprofile/0/kernel: No such file or directory
>  /usr/bin/opcontrol: line 911: /dev/oprofile/0/user: No such file or directory
>  /usr/bin/opcontrol: line 911: /dev/oprofile/0/unit_mask: No such file or directo
>
>  sony:/home/akpm> l /dev/oprofile
>  total 0
>  drwxr-xr-x 1 root root 0 May 13 01:25 1
>  -rw-r--r-- 1 root root 0 May 13 01:25 backtrace_depth
>  -rw-r--r-- 1 root root 0 May 13 01:25 buffer
>  -rw-r--r-- 1 root root 0 May 13 01:25 buffer_size
>  -rw-r--r-- 1 root root 0 May 13 01:25 buffer_watershed
>  -rw-r--r-- 1 root root 0 May 13 01:25 cpu_buffer_size
>  -rw-r--r-- 1 root root 0 May 13 01:25 cpu_type
>  -rw-rw-rw- 1 root root 0 May 13 01:25 dump
>  -rw-r--r-- 1 root root 0 May 13 01:25 enable
>  -rw-r--r-- 1 root root 0 May 13 01:25 pointer_size
>  drwxr-xr-x 1 root root 0 May 13 01:25 stats
>
>  Looks like the "0" got renamed to "1".  Who did that?

There's also a commit d18d00f5dbcd1a95811617e9812cf0560bd465ee with
the following text, which seems related?

"The existing code passed a reference to cpu 0's instance of struct op_msrs
    to model->shutdown, whilst the other functions are passed a reference to
    <this cpu's> instance of a struct op_msrs.  This seemed to be a bug to me
    even though as long as cpu 0 and <this cpu> are of the same type it would
    have the same effect...?"

Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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