linux-kernel - Re: 2.6.27-rc1-mm1: sparc64 BUG: using smp_processor

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Message-Id: <20080803.000232.215078646.davem@davemloft.net>
Date:	Sun, 03 Aug 2008 00:02:32 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	m.kozlowski@...land.pl
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: 2.6.27-rc1-mm1: sparc64 BUG: using smp_processor_id() in
 preemptible code

From: Mariusz Kozlowski <m.kozlowski@...land.pl>
Date: Sat, 2 Aug 2008 17:17:47 +0200

> I'm running preemtible kernel and have seen similar things before:
> http://marc.info/?l=linux-kernel&m=120652827627051&w=2 and it was fixed by disabling
> preemtpion in relevant sparc64 code paths. smp_call_function_mask() documentation
> says it must be called with preemption disabled.
> 
> Here is a similar fix. Compile and run tested.
> 
> Signed-off-by: Mariusz Kozlowski <m.kozlowski@...land.pl>

Thenk for the report and sample patch.

I've decided to put the preemption disabled call at the smp_tsb_sync() call
site so that smp_tsb_sync() can still invoke smp_call_function_mask() as
a tail-call.

Thanks again!

sparc64: Need to disable preemption around smp_tsb_sync().

Based upon a bug report by Mariusz Kozlowski

It uses smp_call_function_masked() now, which has a preemption-disabled
requirement.

Signed-off-by: David S. Miller <davem@...emloft.net>
---
 arch/sparc64/mm/tsb.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/sparc64/mm/tsb.c b/arch/sparc64/mm/tsb.c
index 3547937..587f8ef 100644
--- a/arch/sparc64/mm/tsb.c
+++ b/arch/sparc64/mm/tsb.c
@@ -1,9 +1,10 @@
 /* arch/sparc64/mm/tsb.c
  *
- * Copyright (C) 2006 David S. Miller <davem@...emloft.net>
+ * Copyright (C) 2006, 2008 David S. Miller <davem@...emloft.net>
  */
 
 #include <linux/kernel.h>
+#include <linux/preempt.h>
 #include <asm/system.h>
 #include <asm/page.h>
 #include <asm/tlbflush.h>
@@ -415,7 +416,9 @@ retry_tsb_alloc:
 		tsb_context_switch(mm);
 
 		/* Now force other processors to do the same.  */
+		preempt_disable();
 		smp_tsb_sync(mm);
+		preempt_enable();
 
 		/* Now it is safe to free the old tsb.  */
 		kmem_cache_free(tsb_caches[old_cache_index], old_tsb);
-- 
1.5.6.GIT

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