linux-kernel - Re: [PATCH] Fix dirty page accounting in redirty_page_for

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Date:	Thu, 30 Apr 2009 16:14:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, thomas.pi@...or.dea,
	Yuriy Lalym <ylalym@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ltt-dev@...ts.casi.polymtl.ca, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] Fix dirty page accounting in
	redirty_page_for_writepage()


* Christoph Lameter <cl@...ux.com> wrote:

> On Thu, 30 Apr 2009, Ingo Molnar wrote:
> 
> > it's all done, implemented and upstream already. You are a bit late
> > to the party ;-)
> 
> Just looked over it. Yep, now we just need to fix the things that 
> were messed up.

Could we please skip over the lengthy flamewar and bad-mouthing of 
other people's work and go straight to the constructive portion of 
the discussion? ;-)

The patch below makes the fallback/slowpath irq safe.

	Ingo

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 1581ff2..6b3984a 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -139,17 +139,23 @@ static inline void free_percpu(void *p)
 #ifndef percpu_read
 # define percpu_read(var)						\
   ({									\
+	unsigned long flags;						\
 	typeof(per_cpu_var(var)) __tmp_var__;				\
-	__tmp_var__ = get_cpu_var(var);					\
-	put_cpu_var(var);						\
+									\
+	local_irq_save(flags);						\
+	__tmp_var__ = __get_cpu_var(var);				\
+	local_irq_restore(flags);					\
 	__tmp_var__;							\
   })
 #endif
 
 #define __percpu_generic_to_op(var, val, op)				\
 do {									\
-	get_cpu_var(var) op val;					\
-	put_cpu_var(var);						\
+	unsigned long flags;						\
+									\
+	local_irq_save(flags);						\
+	op val;								\
+	local_irq_restore(flags);					\
 } while (0)
 
 #ifndef percpu_write
--
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