[PATCH] eliminte NMI entry/ exit code

From: George Anzinger <george@mvista.com>
To: lkml <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>
Subject: [PATCH] eliminte NMI entry/ exit code
Date: Fri, 12 Aug 2005 17:45:53 -0700	[thread overview]
Message-ID: <42FD42C1.6040009@mvista.com> (raw)

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The NMI entry and exit code fiddles with bits in the preempt count.  If 
an NMI happens while some other code is doing the same, bits will be 
lost.  This patch removes this modify code from the NMI path till we can 
come up with something better.
-- 
George Anzinger   george@mvista.com
HRT (High-res-timers):  http://sourceforge.net/projects/high-res-timers/

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Source: MontaVista Software, Inc. George Anzinger <george@mvista.com>
Type: Defect Fix 

Description:

    Modifying a word from NMI code runs the very real risk of loosing
    either then new or the old bits.  Remember, we can not prevent an
    NMI interrupt from ANYWHERE, inparticular between the read and the
    write of a read modify write sequence.

    This patch removes the update of the preempt count from the NMI
    path.

Signed-off-by: George Anzinger<george@mvista.com>

 hardirq.h |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

Index: linux-2.6.13-rc/include/linux/hardirq.h
===================================================================

--- linux-2.6.13-rc.orig/include/linux/hardirq.h
+++ linux-2.6.13-rc/include/linux/hardirq.h
@@ -98,9 +98,12 @@ extern void synchronize_irq(unsigned int
 #else
 # define synchronize_irq(irq)	barrier()
 #endif
-
-#define nmi_enter()		irq_enter()
-#define nmi_exit()		sub_preempt_count(HARDIRQ_OFFSET)
+/*
+ * Re think these.  NMI _must_not_ share data words with non-nmi code
+ * Meanwhile, just do a no-op.
+ */
+#define nmi_enter()	/*	irq_enter()  */
+#define nmi_exit()	/*	sub_preempt_count(HARDIRQ_OFFSET) */
 
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
 static inline void account_user_vtime(struct task_struct *tsk)
