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Subject[PATCH 1/2] smp_call_function: don't use lock in call_function_data
There's no need for a lock in call_function_data, since it's only used
to decrement-and-test a counter. Use an atomic instead.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
kernel/smp.c | 17 ++++-------------
1 file changed, 4 insertions(+), 13 deletions(-)

===================================================================
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -10,6 +10,7 @@
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/smp.h>
+#include <asm/atomic.h>

bool __read_mostly smp_single_ipi_queue = false;

@@ -37,8 +38,7 @@

struct call_function_data {
struct call_single_data csd;
- spinlock_t lock;
- unsigned int refs;
+ atomic_t refs;
cpumask_t cpumask;
struct rcu_head rcu_head;
};
@@ -125,21 +125,13 @@
*/
rcu_read_lock();
list_for_each_entry_rcu(data, &queue->list, csd.list) {
- int refs;
-
if (!cpu_isset(cpu, data->cpumask))
continue;

data->csd.func(data->csd.info);

- spin_lock(&data->lock);
cpu_clear(cpu, data->cpumask);
- WARN_ON(data->refs == 0);
- data->refs--;
- refs = data->refs;
- spin_unlock(&data->lock);
-
- if (refs)
+ if (!atomic_dec_and_test(&data->refs))
continue;

spin_lock(&queue->lock);
@@ -379,10 +371,9 @@
slowpath = 1;
}

- spin_lock_init(&data->lock);
data->csd.func = func;
data->csd.info = info;
- data->refs = num_cpus;
+ atomic_set(&data->refs, num_cpus);
data->cpumask = mask;

spin_lock_irqsave(&queue->lock, flags);



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