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List:       lhcs-devel
Subject:    Re: [lhcs-devel] Atomic CPU Hot-Add?
From:       Srivatsa Vaddagiri <vatsa () in ! ibm ! com>
Date:       2004-03-31 9:46:34
Message-ID: 20040331093434.GA21599 () in ! ibm ! com
[Download RAW message or body]

On Tue, Mar 30, 2004 at 08:40:25AM +1000, Rusty Russell wrote:
> I think taking call_lock in __cpu_up() would do for now, and it's well
> contained.  If that's not sufficient, we'll bite the bullet and do the
> whole stop_machine() thing...

Ok ..here's a patch for both ppc64 and x86 to take call_lock before
setting cpu in online_map

PPC64 - Applies against 2.6.5-rc2 present in Ameslab


---

 ameslab-vatsa/arch/ppc64/kernel/smp.c |    2 ++
 1 files changed, 2 insertions(+)

diff -puN arch/ppc64/kernel/smp.c~smp_call_function arch/ppc64/kernel/smp.c
--- ameslab/arch/ppc64/kernel/smp.c~smp_call_function	2004-03-30 15:40:18.000000000 \
                +0530
+++ ameslab-vatsa/arch/ppc64/kernel/smp.c	2004-03-30 15:40:57.000000000 +0530
@@ -1019,7 +1019,9 @@ int __devinit __cpu_up(unsigned int cpu)
 
 	if (smp_ops->give_timebase)
 		smp_ops->give_timebase();
+	spin_lock_irq(&call_lock);
 	cpu_set(cpu, cpu_online_map);
+	spin_unlock_irq(&call_lock);
 	return 0;
 }

x86	- Applies against [2.6.5-rc3 + your i386 patch]

---

 linux-2.6.5-rc3-vatsa/arch/i386/kernel/process.c |    7 ++++++-
 linux-2.6.5-rc3-vatsa/arch/i386/kernel/smp.c     |    2 +-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff -puN arch/i386/kernel/process.c~take_call_lock_before_setting_in_online_map \
                arch/i386/kernel/process.c
--- linux-2.6.5-rc3/arch/i386/kernel/process.c~take_call_lock_before_setting_in_online_map	2004-03-30 \
                16:26:41.000000000 +0530
+++ linux-2.6.5-rc3-vatsa/arch/i386/kernel/process.c	2004-03-30 16:31:53.000000000 \
+0530 @@ -136,6 +136,9 @@ static void poll_idle (void)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
+
+extern spinlock_t call_lock;
+
 /* We don't actually take CPU down, just spin without interrupts. */
 static void play_dead(void)
 {
@@ -152,8 +155,10 @@ static void play_dead(void)
 		cpu_relax();
 
 	local_irq_disable();
-	__flush_tlb_all();
+	spin_lock(&call_lock);
 	cpu_set(smp_processor_id(), cpu_online_map);
+	spin_unlock(&call_lock);
+	__flush_tlb_all();
 	apic_start();
 	local_irq_enable();
 	enable_timer_nmi_watchdog();
diff -puN arch/i386/kernel/smp.c~take_call_lock_before_setting_in_online_map \
                arch/i386/kernel/smp.c
--- linux-2.6.5-rc3/arch/i386/kernel/smp.c~take_call_lock_before_setting_in_online_map	2004-03-30 \
                16:26:41.000000000 +0530
+++ linux-2.6.5-rc3-vatsa/arch/i386/kernel/smp.c	2004-03-30 16:27:00.000000000 +0530
@@ -485,7 +485,7 @@ void smp_send_reschedule(int cpu)
  * Structure and data for smp_call_function(). This is designed to minimise
  * static memory requirements. It also looks cleaner.
  */
-static spinlock_t call_lock = SPIN_LOCK_UNLOCKED;
+spinlock_t call_lock = SPIN_LOCK_UNLOCKED;
 
 struct call_data_struct {
 	void (*func) (void *info);


-- 


Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017


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