linux-kernel - [PATCH] percpu: fix DEBUG_PREEMPT per

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Message-ID: <Pine.LNX.4.64.0802231927500.13934@blonde.site>
Date:	Sat, 23 Feb 2008 19:40:17 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Mike Travis <travis@....com>, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] percpu: fix DEBUG_PREEMPT per_cpu checking

2.6.25-rc1 percpu changes broke CONFIG_DEBUG_PREEMPT's per_cpu checking
on several architectures.  On s390, sparc64 and x86 it's been weakened to
not checking at all; whereas on powerpc64 it's become too strict, issuing
warnings from __raw_get_cpu_var in io_schedule and init_timer for example.

Fix this by weakening powerpc's __my_cpu_offset to use the non-checking
local_paca instead of get_paca (which itself contains such a check);
and strengthening the generic my_cpu_offset to go the old slow way via
smp_processor_id when CONFIG_DEBUG_PREEMPT (debug_smp_processor_id is
where all the knowledge of what's correct when lives).

Signed-off-by: Hugh Dickins <hugh@...itas.com>
Reviewed-by: Mike Travis <travis@....com>
---
I posted this a couple of weeks ago, but it seems we all expected
someone else to forward it to you.

 include/asm-generic/percpu.h |    2 ++
 include/asm-powerpc/percpu.h |    2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

--- 2.6.25-rc2-git/include/asm-generic/percpu.h	2008-02-08 11:31:30.000000000 +0000
+++ linux/include/asm-generic/percpu.h	2008-02-08 12:27:08.000000000 +0000
@@ -32,6 +32,8 @@ extern unsigned long __per_cpu_offset[NR
  */
 #ifndef __my_cpu_offset
 #define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
+#endif
+#ifdef CONFIG_DEBUG_PREEMPT
 #define my_cpu_offset per_cpu_offset(smp_processor_id())
 #else
 #define my_cpu_offset __my_cpu_offset
--- 2.6.25-rc2-git/include/asm-powerpc/percpu.h	2008-02-08 11:31:31.000000000 +0000
+++ linux/include/asm-powerpc/percpu.h	2008-02-08 12:29:17.000000000 +0000
@@ -13,7 +13,7 @@
 #include <asm/paca.h>
 
 #define __per_cpu_offset(cpu) (paca[cpu].data_offset)
-#define __my_cpu_offset get_paca()->data_offset
+#define __my_cpu_offset local_paca->data_offset
 #define per_cpu_offset(x) (__per_cpu_offset(x))
 
 #endif /* CONFIG_SMP */
--
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