Date: Wed, 25 Mar 2009 14:13:30 +0100
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>, rusty@rustcorp.com.au, tglx@linutronix.de,
       x86@kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com,
       Paul Mundt <lethal@linux-sh.org>, rmk@arm.linux.org.uk,
       starvik@axis.com, ralf@linux-mips.org, davem@davemloft.net,
       cooloney@kernel.org, kyle@mcmartin.ca, matthew@wil.cx,
       grundler@parisc-linux.org, takata@linux-m32r.org,
       benh@kernel.crashing.org, rth@twiddle.net, ink@jurassic.park.msu.ru,
       heiko.carstens@de.ibm.com
Subject: Re: [GIT RFC] percpu: use dynamic percpu allocator as the default
 percpu allocator
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On Wed, 25 Mar 2009 21:27:49 +0900
Tejun Heo <tj@kernel.org> wrote:

> Ingo Molnar wrote:
> > * Tejun Heo <tj@kernel.org> wrote:
> > 
> >>> With your patches and a RELOC_HIDE version that uses the GOTENT 
> >>> indirection the kernel won't compile because the "X" constraint 
> >>> for the GOTENT access needs a symbol and there are quite a few 
> >>> users that pass a pointer. I do not see a simple solution for 
> >>> that problem yet.
> >> Ah... okay.  Now I get it.  It wasn't expecting variables there.  How
> >> about doing the following?
> >>
> >>  #define SHIFT_PERCPU_PTR(ptr, offset) (({				\
> >> 	 if (__builtin_constant_p(ptr))					\
> >> 		 do GOTENT trick;					\
> >> 	 else								\
> >> 		 RELOC_HIDE();						\
> >>  }))
> >>
> >> Thanks.
> > 
> > Btw., is there any intermediate fix/workaround i could apply 
> > perhaps? I'd like to send the percpu bits early in the merge window 
> > and would hate to break Martin's arch ...
> 
> Martin's original patch should do the trick although it would be
> slower for static symbols.  I'll merge it and post the tree.

No, my original patch doesn't work. It will break modules that use
static per-cpu variables.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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