linux-kernel - Re: [Cbe-oss-dev] powerpc/cell/oprofile: fix mutex locking for spu-oprofile

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Message-ID: <18610.20951.764057.574721@cargo.ozlabs.ibm.com>
Date:	Mon, 25 Aug 2008 16:31:51 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	cbe-oss-dev@...abs.org, Robert Richter <robert.richter@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org, oprofile-list@...ts.sourceforge.net,
	cel <cel@...ux.vnet.ibm.com>
Subject: Re: [Cbe-oss-dev] powerpc/cell/oprofile: fix mutex locking for spu-oprofile

Arnd Bergmann writes:

> The patch does not fix a regression, the spu-oprofile code basically never
> worked. With the current code in Linux, samples in the profile buffer
> can get corrupted because reader and writer to that buffer use different
> locks for accessing it. It took us several iterations to come up with
> a solution that does not introduce other problems and I didn't want to
> push an earlier version that would need more fixups.
> 
> Since rc4 is out now, I understand if you feel more comfortable with
> putting the patch into -next instead of -merge.

Linus has been getting stricter about only putting in fixes for
regressions and serious bugs (see his recent email to Dave Airlie on
LKML for instance).  I assume that the corruption is just in the data
that is supplied to userspace and doesn't extend to any kernel data
structures.  If it does then we have a much stronger argument for
pushing this stuff for 2.6.27.

> Note that the second patch is trivial and fixes an oopsable condition
> of the kernel, so at least that should still go into 2.6.27.

OK, I'll cherry-pick that one for my next batch for Linus.

Paul.
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