linux-kernel - Re: [patch] x86_64: do not enable the NMI watchdog by default

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Date:	Thu, 7 Dec 2006 21:47:45 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>
Cc:	Alan <alan@...rguk.ukuu.org.uk>, Len Brown <lenb@...nel.org>,
	linux-kernel@...r.kernel.org, ak@...e.de,
	Linus Torvalds <torvalds@...l.org>
Subject: Re: [patch] x86_64: do not enable the NMI watchdog by default


* Andrew Morton <akpm@...l.org> wrote:

> (the patch doesn't vaguely apply btw).

patch below should apply to tail of current-ish -mm. Build and boot 
tested on x86_64.

	Ingo

---------------------->
Subject: [patch] x86_64: do not enable the NMI watchdog by default
From: Ingo Molnar <mingo@...e.hu>

do not enable the NMI watchdog by default. Now that we have
lockdep i cannot remember the last time it caught a real bug,
but the NMI watchdog can /cause/ problems. Furthermore, to the
typical user, an NMI watchdog assert results in a total lockup
anyway (if under X). In that sense, all that the NMI watchdog
does is that it makes the system /less/ stable and /less/
debuggable.

people can still enable it either after bootup via:

   echo 1 > /proc/sys/kernel/nmi

or via the nmi_watchdog=1 or nmi_watchdog=2 boot options.

build and boot tested on an Athlon64 box.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86_64/kernel/apic.c    |    1 -
 arch/x86_64/kernel/io_apic.c |    1 -
 arch/x86_64/kernel/nmi.c     |    2 +-
 arch/x86_64/kernel/smpboot.c |    1 -
 include/asm-x86_64/nmi.h     |    1 -
 5 files changed, 1 insertion(+), 5 deletions(-)

Index: linux-mm-genapic.q/arch/x86_64/kernel/apic.c
===================================================================
--- linux-mm-genapic.q.orig/arch/x86_64/kernel/apic.c
+++ linux-mm-genapic.q/arch/x86_64/kernel/apic.c
@@ -427,7 +427,6 @@ void __cpuinit setup_local_APIC (void)
 			oldvalue, value);
 	}
 
-	nmi_watchdog_default();
 	setup_apic_nmi_watchdog(NULL);
 	apic_pm_activate();
 }
Index: linux-mm-genapic.q/arch/x86_64/kernel/io_apic.c
===================================================================
--- linux-mm-genapic.q.orig/arch/x86_64/kernel/io_apic.c
+++ linux-mm-genapic.q/arch/x86_64/kernel/io_apic.c
@@ -1580,7 +1580,6 @@ static int try_apic_pin(int apic, int pi
 	 * Ok, does IRQ0 through the IOAPIC work?
 	 */
 	if (!no_timer_check && timer_irq_works()) {
-		nmi_watchdog_default();
 		if (nmi_watchdog == NMI_IO_APIC) {
 			disable_8259A_irq(0);
 			setup_nmi();
Index: linux-mm-genapic.q/arch/x86_64/kernel/nmi.c
===================================================================
--- linux-mm-genapic.q.orig/arch/x86_64/kernel/nmi.c
+++ linux-mm-genapic.q/arch/x86_64/kernel/nmi.c
@@ -183,7 +183,7 @@ static __cpuinit inline int nmi_known_cp
 }
 
 /* Run after command line and cpu_init init, but before all other checks */
-void nmi_watchdog_default(void)
+static inline void nmi_watchdog_default(void)
 {
 	if (nmi_watchdog != NMI_DEFAULT)
 		return;
Index: linux-mm-genapic.q/arch/x86_64/kernel/smpboot.c
===================================================================
--- linux-mm-genapic.q.orig/arch/x86_64/kernel/smpboot.c
+++ linux-mm-genapic.q/arch/x86_64/kernel/smpboot.c
@@ -1080,7 +1080,6 @@ static int __init smp_sanity_check(unsig
  */
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
-	nmi_watchdog_default();
 	current_cpu_data = boot_cpu_data;
 	current_thread_info()->cpu = 0;  /* needed? */
 	set_cpu_sibling_map(0);
Index: linux-mm-genapic.q/include/asm-x86_64/nmi.h
===================================================================
--- linux-mm-genapic.q.orig/include/asm-x86_64/nmi.h
+++ linux-mm-genapic.q/include/asm-x86_64/nmi.h
@@ -59,7 +59,6 @@ extern void disable_timer_nmi_watchdog(v
 extern void enable_timer_nmi_watchdog(void);
 extern int nmi_watchdog_tick (struct pt_regs * regs, unsigned reason);
 
-extern void nmi_watchdog_default(void);
 extern int setup_nmi_watchdog(char *);
 
 extern atomic_t nmi_active;
-
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