linux-kernel - Re: [PATCH] Fix for OProfile callgraph for Power 64 bit user apps

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Message-ID: <18476.5290.709729.582063@cargo.ozlabs.ibm.com>
Date:	Thu, 15 May 2008 20:47:06 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Carl Love <cel@...ibm.com>
Cc:	linuxppc-dev <linuxppc-dev@...abs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Maynard Johnson <maynardj@...ibm.com>
Subject: Re: [PATCH] Fix for OProfile callgraph for Power 64 bit user apps

Carl Love writes:

> The following patch fixes the 64 bit user code backtrace 
> which currently may hang the system.  

What exactly is wrong with it?

Having now taken a much closer look, I now don't think Nate Case's
patch addresses this, since it only affects constant size arguments
<= 8 to copy_{to,from}_user_inatomic.

However, I don't see why your patch fixes anything.  It means we do
two access_ok calls and two __copy_from_user_inatomic calls, for 8
bytes, at sp and at sp + 16, rather than doing one access_ok and
__copy_from_user_inatomic for 24 bytes at sp.  Why does that make any
difference (apart from being slower)?

Paul.
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