linux-kernel - Re: Oprofile Regression Caused by commit e5d1367f17ba6a6fed5fd8b74e4d5720923e0c25 on PPC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20111012165154.GB6158@mgebm.net>
Date:	Wed, 12 Oct 2011 12:51:54 -0400
From:	Eric B Munson <emunson@...bm.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	eranian@...gle.com, mingo@...e.hu, anton@...ba.org,
	linux-kernel@...r.kernel.org, paulus@...ba.org, hbabu@...ibm.com
Subject: Re: Oprofile Regression Caused by commit
 e5d1367f17ba6a6fed5fd8b74e4d5720923e0c25 on PPC

On Tue, 11 Oct 2011, Peter Zijlstra wrote:

> On Mon, 2011-10-10 at 19:38 -0400, Eric B Munson wrote:
> > On Fri, 07 Oct 2011, Eric B Munson wrote:
> > 
> > > This commit seems to have caused a regression with oprofile.  It is fairly easy
> > > to trigger, simply run oprofile monitoring an event that will fire (something
> > > frequent like CPU cycles) causes oprofile to fail saying that the PMU is in use.
> > > If I disable CONFIG_CGROUP_PERF, everything goes back to working.  I suspect the
> > > problem is that the PMU is being initialized without being reserved for perf.  I
> > > am not yet sure of the right fix yet so if you have any suggestions I would
> > > appreciate them.
> > > 
> > > Eric
> > 
> > This isn't the best description of the behavior we see, what happens is at some
> > point in the profiling session the MMCR register is clobbered by
> > perf_cgroup_switch() which calls perf_pmu_enable() without reserving the PMC
> > hardware.  When this happens oprofile stops counting.  It doesn't happen each
> > time so some runs show event counts that are reasonable, but it can also lead to
> > event counts that are smaller than expected, or completely missing.
> 
> What kernel are you testing?
> 

The problem seems to be fixed in 3.1-rc9 so I just need to identify the
patch(es) that fixed it.

Eric

Download attachment "signature.asc" of type "application/pgp-signature" (837 bytes)