[PATCH 0/3] x86, reboot: Modify shutting down cpus

[PATCH 0/3] x86, reboot: Modify shutting down cpus

[Don Zickus]

This patch set breaks apart my earlier attempt to modify shutting
down cpus during panic into a simple revert and a new patch.  This
makes it easier to follow the changes I am doing.

Don Zickus (3):
  Revert "x86, reboot: Use NMI instead of REBOOT_VECTOR to stop cpus"
  x86, reboot: use NMI to assist in shutting down if IRQ fails
  x86, reboot:  Update nonmi_ipi parameter

 arch/x86/kernel/smp.c |  100 ++++++++++++++++++++++--------------------------
 1 files changed, 46 insertions(+), 54 deletions(-)

-- 
1.7.7.6

[PATCH 1/3] Revert "x86, reboot: Use NMI instead of REBOOT_VECTOR to stop cpus"

[Don Zickus]

This reverts commit 3603a2512f9e69dc87914ba922eb4a0812b21cd6.

Originally I wanted a better hammer to shutdown cpus during panic.
However, this really steps on the toes of various spinlocks in the
panic path.  Sometimes it is easier to wait for the IRQ to become
re-enabled to indictate the cpu left the critical region and then
shutdown the cpu.

The next patch moves the NMI addition after the IRQ part.  To make
it easier to see the logic of everything, revert this patch and
apply the next simpler patch.

Signed-off-by: Don Zickus <dzickus@redhat.com>
---
 arch/x86/kernel/smp.c |   59 +-----------------------------------------------
 1 files changed, 2 insertions(+), 57 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 66c74f4..6d20f52 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -29,7 +29,6 @@
 #include <asm/mmu_context.h>
 #include <asm/proto.h>
 #include <asm/apic.h>
-#include <asm/nmi.h>
 /*
  *	Some notes on x86 processor bugs affecting SMP operation:
  *
@@ -149,60 +148,6 @@ void native_send_call_func_ipi(const struct cpumask *mask)
 	free_cpumask_var(allbutself);
 }
 
-static atomic_t stopping_cpu = ATOMIC_INIT(-1);
-
-static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs)
-{
-	/* We are registered on stopping cpu too, avoid spurious NMI */
-	if (raw_smp_processor_id() == atomic_read(&stopping_cpu))
-		return NMI_HANDLED;
-
-	stop_this_cpu(NULL);
-
-	return NMI_HANDLED;
-}
-
-static void native_nmi_stop_other_cpus(int wait)
-{
-	unsigned long flags;
-	unsigned long timeout;
-
-	if (reboot_force)
-		return;
-
-	/*
-	 * Use an own vector here because smp_call_function
-	 * does lots of things not suitable in a panic situation.
-	 */
-	if (num_online_cpus() > 1) {
-		/* did someone beat us here? */
-		if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1)
-			return;
-
-		if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback,
-					 NMI_FLAG_FIRST, "smp_stop"))
-			/* Note: we ignore failures here */
-			return;
-
-		/* sync above data before sending NMI */
-		wmb();
-
-		apic->send_IPI_allbutself(NMI_VECTOR);
-
-		/*
-		 * Don't wait longer than a second if the caller
-		 * didn't ask us to wait.
-		 */
-		timeout = USEC_PER_SEC;
-		while (num_online_cpus() > 1 && (wait || timeout--))
-			udelay(1);
-	}
-
-	local_irq_save(flags);
-	disable_local_APIC();
-	local_irq_restore(flags);
-}
-
 /*
  * this function calls the 'stop' function on all other CPUs in the system.
  */
@@ -215,7 +160,7 @@ asmlinkage void smp_reboot_interrupt(void)
 	irq_exit();
 }
 
-static void native_irq_stop_other_cpus(int wait)
+static void native_stop_other_cpus(int wait)
 {
 	unsigned long flags;
 	unsigned long timeout;
@@ -298,7 +243,7 @@ struct smp_ops smp_ops = {
 	.smp_prepare_cpus	= native_smp_prepare_cpus,
 	.smp_cpus_done		= native_smp_cpus_done,
 
-	.stop_other_cpus	= native_nmi_stop_other_cpus,
+	.stop_other_cpus	= native_stop_other_cpus,
 	.smp_send_reschedule	= native_smp_send_reschedule,
 
 	.cpu_up			= native_cpu_up,
-- 
1.7.7.6

[tip:x86/reboot] Revert "x86, reboot: Use NMI instead of REBOOT_VECTOR to stop cpus"

[tip-bot for Don Zickus]

Commit-ID:  5d2b86d90f7cc4a41316cef3d41560da6141f45c
Gitweb:     http://git.kernel.org/tip/5d2b86d90f7cc4a41316cef3d41560da6141f45c
Author:     Don Zickus <dzickus@redhat.com>
AuthorDate: Fri, 11 May 2012 14:41:13 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 14 May 2012 11:49:37 +0200

Revert "x86, reboot: Use NMI instead of REBOOT_VECTOR to stop cpus"

This reverts commit 3603a2512f9e69dc87914ba922eb4a0812b21cd6.

Originally I wanted a better hammer to shutdown cpus during
panic. However, this really steps on the toes of various
spinlocks in the panic path.  Sometimes it is easier to wait for
the IRQ to become re-enabled to indictate the cpu left the
critical region and then shutdown the cpu.

The next patch moves the NMI addition after the IRQ part.  To
make it easier to see the logic of everything, revert this patch
and apply the next simpler patch.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1336761675-24296-2-git-send-email-dzickus@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/smp.c |   59 +-----------------------------------------------
 1 files changed, 2 insertions(+), 57 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 66c74f4..6d20f52 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -29,7 +29,6 @@
 #include <asm/mmu_context.h>
 #include <asm/proto.h>
 #include <asm/apic.h>
-#include <asm/nmi.h>
 /*
  *	Some notes on x86 processor bugs affecting SMP operation:
  *
@@ -149,60 +148,6 @@ void native_send_call_func_ipi(const struct cpumask *mask)
 	free_cpumask_var(allbutself);
 }
 
-static atomic_t stopping_cpu = ATOMIC_INIT(-1);
-
-static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs)
-{
-	/* We are registered on stopping cpu too, avoid spurious NMI */
-	if (raw_smp_processor_id() == atomic_read(&stopping_cpu))
-		return NMI_HANDLED;
-
-	stop_this_cpu(NULL);
-
-	return NMI_HANDLED;
-}
-
-static void native_nmi_stop_other_cpus(int wait)
-{
-	unsigned long flags;
-	unsigned long timeout;
-
-	if (reboot_force)
-		return;
-
-	/*
-	 * Use an own vector here because smp_call_function
-	 * does lots of things not suitable in a panic situation.
-	 */
-	if (num_online_cpus() > 1) {
-		/* did someone beat us here? */
-		if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1)
-			return;
-
-		if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback,
-					 NMI_FLAG_FIRST, "smp_stop"))
-			/* Note: we ignore failures here */
-			return;
-
-		/* sync above data before sending NMI */
-		wmb();
-
-		apic->send_IPI_allbutself(NMI_VECTOR);
-
-		/*
-		 * Don't wait longer than a second if the caller
-		 * didn't ask us to wait.
-		 */
-		timeout = USEC_PER_SEC;
-		while (num_online_cpus() > 1 && (wait || timeout--))
-			udelay(1);
-	}
-
-	local_irq_save(flags);
-	disable_local_APIC();
-	local_irq_restore(flags);
-}
-
 /*
  * this function calls the 'stop' function on all other CPUs in the system.
  */
@@ -215,7 +160,7 @@ asmlinkage void smp_reboot_interrupt(void)
 	irq_exit();
 }
 
-static void native_irq_stop_other_cpus(int wait)
+static void native_stop_other_cpus(int wait)
 {
 	unsigned long flags;
 	unsigned long timeout;
@@ -298,7 +243,7 @@ struct smp_ops smp_ops = {
 	.smp_prepare_cpus	= native_smp_prepare_cpus,
 	.smp_cpus_done		= native_smp_cpus_done,
 
-	.stop_other_cpus	= native_nmi_stop_other_cpus,
+	.stop_other_cpus	= native_stop_other_cpus,
 	.smp_send_reschedule	= native_smp_send_reschedule,
 
 	.cpu_up			= native_cpu_up,

[PATCH 2/3] x86, reboot: Use NMI to assist in shutting down if IRQ fails

[Don Zickus]

x86, reboot: revert stop_other_cpus to using IRQ with NMI fallback

For v3.3, I added code to use the NMI to stop other cpus in the panic
case.  The idea was to make sure all cpus on the system were definitely
halted to help serialize the panic path to execute the rest of the
code on a single cpu.

The main problem it was trying to solve was how to stop a cpu that
was spinning with its irqs disabled.  A IPI irq would be stuck and
couldn't get in there, but an NMI could.

Things were great until we had another conversation about some pstore
changes.  Because some of the backend pstore still uses spinlocks to
protect the device access, things could get ugly if a panic happened
and we were stuck spinning on a lock.

Now with the NMI shutting down cpus, we could assume no other cpus were
running and just bust the spin lock and proceed.

The counter argument was, well if you do that the backend could be in
a screwed up state and you might not be able to save anything as a result.
If we could have just given the cpu a little more time to finish things,
we could have grabbed the spin lock cleanly and everything would have been
fine.

Well, how do give a cpu a 'little more time' in the panic case?  For the
most part you can't without spinning on the lock and even in that case,
how long do you spin for?

So instead of making it ugly in the pstore code, just mimic the idea that
stop_machine had, which is block on an IRQ IPI until the remote cpu has
re-enabled interrupts and left the critical region.  Which is what happens
now using REBOOT_IRQ.

Then leave the NMI case for those cpus that are truly stuck after a short
time.  This leaves the current behaviour alone and just handle a corner
case.  Most systems should never have to enter the NMI code and if they
do, print out a message in case the NMI itself causes another issue.

Signed-off-by: Don Zickus <dzickus@redhat.com>
---
 arch/x86/kernel/smp.c |   61 +++++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 6d20f52..228e740 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -29,6 +29,7 @@
 #include <asm/mmu_context.h>
 #include <asm/proto.h>
 #include <asm/apic.h>
+#include <asm/nmi.h>
 /*
  *	Some notes on x86 processor bugs affecting SMP operation:
  *
@@ -108,6 +109,8 @@
  *	about nothing of note with C stepping upwards.
  */
 
+static atomic_t stopping_cpu = ATOMIC_INIT(-1);
+
 /*
  * this function sends a 'reschedule' IPI to another CPU.
  * it goes straight through and wastes no time serializing
@@ -148,6 +151,17 @@ void native_send_call_func_ipi(const struct cpumask *mask)
 	free_cpumask_var(allbutself);
 }
 
+static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs)
+{
+	/* We are registered on stopping cpu too, avoid spurious NMI */
+	if (raw_smp_processor_id() == atomic_read(&stopping_cpu))
+		return NMI_HANDLED;
+
+	stop_this_cpu(NULL);
+
+	return NMI_HANDLED;
+}
+
 /*
  * this function calls the 'stop' function on all other CPUs in the system.
  */
@@ -171,13 +185,25 @@ static void native_stop_other_cpus(int wait)
 	/*
 	 * Use an own vector here because smp_call_function
 	 * does lots of things not suitable in a panic situation.
-	 * On most systems we could also use an NMI here,
-	 * but there are a few systems around where NMI
-	 * is problematic so stay with an non NMI for now
-	 * (this implies we cannot stop CPUs spinning with irq off
-	 * currently)
+	 */
+
+	/*
+	 * We start by using the REBOOT_VECTOR irq.
+	 * The irq is treated as a sync point to allow critical
+	 * regions of code on other cpus to release their spin locks
+	 * and re-enable irqs.  Jumping straight to an NMI might
+	 * accidentally cause deadlocks with further shutdown/panic
+	 * code.  By syncing, we give the cpus up to one second to
+	 * finish their work before we force them off with the NMI.
 	 */
 	if (num_online_cpus() > 1) {
+		/* did someone beat us here? */
+		if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1)
+			return;
+
+		/* sync above data before sending IRQ */
+		wmb();
+
 		apic->send_IPI_allbutself(REBOOT_VECTOR);
 
 		/*
@@ -188,7 +214,32 @@ static void native_stop_other_cpus(int wait)
 		while (num_online_cpus() > 1 && (wait || timeout--))
 			udelay(1);
 	}
+	
+	/* if the REBOOT_VECTOR didn't work, try with the NMI */
+	if ((num_online_cpus() > 1))  {
+		if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback,
+					 NMI_FLAG_FIRST, "smp_stop"))
+			/* Note: we ignore failures here */
+			/* Hope the REBOOT_IRQ is good enough */
+			goto finish;
+
+		/* sync above data before sending IRQ */
+		wmb();
+
+		pr_emerg("Shutting down cpus with NMI\n");
+
+		apic->send_IPI_allbutself(NMI_VECTOR);
+
+		/*
+		 * Don't wait longer than a 10 ms if the caller
+		 * didn't ask us to wait.
+		 */
+		timeout = USEC_PER_MSEC * 10;
+		while (num_online_cpus() > 1 && (wait || timeout--))
+			udelay(1);
+	}
 
+finish:
 	local_irq_save(flags);
 	disable_local_APIC();
 	local_irq_restore(flags);
-- 
1.7.7.6

[tip:x86/reboot] x86/reboot: Use NMI to assist in shutting down if IRQ fails

[tip-bot for Don Zickus]

Commit-ID:  7d007d21e539dbecb6942c5734e6649f720982cf
Gitweb:     http://git.kernel.org/tip/7d007d21e539dbecb6942c5734e6649f720982cf
Author:     Don Zickus <dzickus@redhat.com>
AuthorDate: Fri, 11 May 2012 14:41:14 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 14 May 2012 11:49:37 +0200

x86/reboot: Use NMI to assist in shutting down if IRQ fails

For v3.3, I added code to use the NMI to stop other cpus in the
panic case.  The idea was to make sure all cpus on the system
were definitely halted to help serialize the panic path to
execute the rest of the code on a single cpu.

The main problem it was trying to solve was how to stop a cpu
that was spinning with its irqs disabled.  A IPI irq would be
stuck and couldn't get in there, but an NMI could.

Things were great until we had another conversation about some
pstore changes.  Because some of the backend pstore still uses
spinlocks to protect the device access, things could get ugly if
a panic happened and we were stuck spinning on a lock.

Now with the NMI shutting down cpus, we could assume no other
cpus were running and just bust the spin lock and proceed.

The counter argument was, well if you do that the backend could
be in a screwed up state and you might not be able to save
anything as a result. If we could have just given the cpu a
little more time to finish things, we could have grabbed the
spin lock cleanly and everything would have been fine.

Well, how do give a cpu a 'little more time' in the panic case?
For the most part you can't without spinning on the lock and
even in that case, how long do you spin for?

So instead of making it ugly in the pstore code, just mimic the
idea that stop_machine had, which is block on an IRQ IPI until
the remote cpu has re-enabled interrupts and left the critical
region.  Which is what happens now using REBOOT_IRQ.

Then leave the NMI case for those cpus that are truly stuck
after a short time.  This leaves the current behaviour alone and
just handle a corner case.  Most systems should never have to
enter the NMI code and if they do, print out a message in case
the NMI itself causes another issue.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1336761675-24296-3-git-send-email-dzickus@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/smp.c |   61 +++++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 6d20f52..228e740 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -29,6 +29,7 @@
 #include <asm/mmu_context.h>
 #include <asm/proto.h>
 #include <asm/apic.h>
+#include <asm/nmi.h>
 /*
  *	Some notes on x86 processor bugs affecting SMP operation:
  *
@@ -108,6 +109,8 @@
  *	about nothing of note with C stepping upwards.
  */
 
+static atomic_t stopping_cpu = ATOMIC_INIT(-1);
+
 /*
  * this function sends a 'reschedule' IPI to another CPU.
  * it goes straight through and wastes no time serializing
@@ -148,6 +151,17 @@ void native_send_call_func_ipi(const struct cpumask *mask)
 	free_cpumask_var(allbutself);
 }
 
+static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs)
+{
+	/* We are registered on stopping cpu too, avoid spurious NMI */
+	if (raw_smp_processor_id() == atomic_read(&stopping_cpu))
+		return NMI_HANDLED;
+
+	stop_this_cpu(NULL);
+
+	return NMI_HANDLED;
+}
+
 /*
  * this function calls the 'stop' function on all other CPUs in the system.
  */
@@ -171,13 +185,25 @@ static void native_stop_other_cpus(int wait)
 	/*
 	 * Use an own vector here because smp_call_function
 	 * does lots of things not suitable in a panic situation.
-	 * On most systems we could also use an NMI here,
-	 * but there are a few systems around where NMI
-	 * is problematic so stay with an non NMI for now
-	 * (this implies we cannot stop CPUs spinning with irq off
-	 * currently)
+	 */
+
+	/*
+	 * We start by using the REBOOT_VECTOR irq.
+	 * The irq is treated as a sync point to allow critical
+	 * regions of code on other cpus to release their spin locks
+	 * and re-enable irqs.  Jumping straight to an NMI might
+	 * accidentally cause deadlocks with further shutdown/panic
+	 * code.  By syncing, we give the cpus up to one second to
+	 * finish their work before we force them off with the NMI.
 	 */
 	if (num_online_cpus() > 1) {
+		/* did someone beat us here? */
+		if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1)
+			return;
+
+		/* sync above data before sending IRQ */
+		wmb();
+
 		apic->send_IPI_allbutself(REBOOT_VECTOR);
 
 		/*
@@ -188,7 +214,32 @@ static void native_stop_other_cpus(int wait)
 		while (num_online_cpus() > 1 && (wait || timeout--))
 			udelay(1);
 	}
+	
+	/* if the REBOOT_VECTOR didn't work, try with the NMI */
+	if ((num_online_cpus() > 1))  {
+		if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback,
+					 NMI_FLAG_FIRST, "smp_stop"))
+			/* Note: we ignore failures here */
+			/* Hope the REBOOT_IRQ is good enough */
+			goto finish;
+
+		/* sync above data before sending IRQ */
+		wmb();
+
+		pr_emerg("Shutting down cpus with NMI\n");
+
+		apic->send_IPI_allbutself(NMI_VECTOR);
+
+		/*
+		 * Don't wait longer than a 10 ms if the caller
+		 * didn't ask us to wait.
+		 */
+		timeout = USEC_PER_MSEC * 10;
+		while (num_online_cpus() > 1 && (wait || timeout--))
+			udelay(1);
+	}
 
+finish:
 	local_irq_save(flags);
 	disable_local_APIC();
 	local_irq_restore(flags);

[PATCH 3/3] x86, reboot: Update nonmi_ipi parameter

[Don Zickus]

Update the nonmi_ipi parameter to reflect the simple change instead
of the previous complicated one.  There should be less of a need to
use it but there may still be corner cases on older hardware that
stumble into NMI issues.

Signed-off-by: Don Zickus <dzickus@redhat.com>
---
 arch/x86/kernel/smp.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 228e740..48d2b7d 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -110,6 +110,7 @@
  */
 
 static atomic_t stopping_cpu = ATOMIC_INIT(-1);
+static bool smp_no_nmi_ipi = false;
 
 /*
  * this function sends a 'reschedule' IPI to another CPU.
@@ -216,7 +217,7 @@ static void native_stop_other_cpus(int wait)
 	}
 	
 	/* if the REBOOT_VECTOR didn't work, try with the NMI */
-	if ((num_online_cpus() > 1))  {
+	if ((num_online_cpus() > 1) && (!smp_no_nmi_ipi))  {
 		if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback,
 					 NMI_FLAG_FIRST, "smp_stop"))
 			/* Note: we ignore failures here */
@@ -245,11 +246,6 @@ finish:
 	local_irq_restore(flags);
 }
 
-static void native_smp_disable_nmi_ipi(void)
-{
-	smp_ops.stop_other_cpus = native_irq_stop_other_cpus;
-}
-
 /*
  * Reschedule call back.
  */
@@ -283,8 +279,8 @@ void smp_call_function_single_interrupt(struct pt_regs *regs)
 
 static int __init nonmi_ipi_setup(char *str)
 {
-        native_smp_disable_nmi_ipi();
-        return 1;
+	smp_no_nmi_ipi = true;
+	return 1;
 }
 
 __setup("nonmi_ipi", nonmi_ipi_setup);
-- 
1.7.7.6

[tip:x86/reboot] x86/reboot: Update nonmi_ipi parameter

[tip-bot for Don Zickus]

Commit-ID:  3aac27aba79b7c52e709ef6de0f7d8139caedc01
Gitweb:     http://git.kernel.org/tip/3aac27aba79b7c52e709ef6de0f7d8139caedc01
Author:     Don Zickus <dzickus@redhat.com>
AuthorDate: Fri, 11 May 2012 14:41:15 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 14 May 2012 11:49:38 +0200

x86/reboot: Update nonmi_ipi parameter

Update the nonmi_ipi parameter to reflect the simple change
instead of the previous complicated one.  There should be less
of a need to use it but there may still be corner cases on older
hardware that stumble into NMI issues.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1336761675-24296-4-git-send-email-dzickus@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/smp.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 228e740..48d2b7d 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -110,6 +110,7 @@
  */
 
 static atomic_t stopping_cpu = ATOMIC_INIT(-1);
+static bool smp_no_nmi_ipi = false;
 
 /*
  * this function sends a 'reschedule' IPI to another CPU.
@@ -216,7 +217,7 @@ static void native_stop_other_cpus(int wait)
 	}
 	
 	/* if the REBOOT_VECTOR didn't work, try with the NMI */
-	if ((num_online_cpus() > 1))  {
+	if ((num_online_cpus() > 1) && (!smp_no_nmi_ipi))  {
 		if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback,
 					 NMI_FLAG_FIRST, "smp_stop"))
 			/* Note: we ignore failures here */
@@ -245,11 +246,6 @@ finish:
 	local_irq_restore(flags);
 }
 
-static void native_smp_disable_nmi_ipi(void)
-{
-	smp_ops.stop_other_cpus = native_irq_stop_other_cpus;
-}
-
 /*
  * Reschedule call back.
  */
@@ -283,8 +279,8 @@ void smp_call_function_single_interrupt(struct pt_regs *regs)
 
 static int __init nonmi_ipi_setup(char *str)
 {
-        native_smp_disable_nmi_ipi();
-        return 1;
+	smp_no_nmi_ipi = true;
+	return 1;
 }
 
 __setup("nonmi_ipi", nonmi_ipi_setup);