On Wed, Dec 21, 2011 at 12:42:04AM +0530, Srivatsa S. Bhat wrote:
> register_hotcpu_notifier(...);
> grab spinlock
> for_each_online_cpu(N)
> add N to bitmap
> release spinlock
>
> because the latter code is not fully race-free (because we don't handle
> CPU_DOWN_PREPARE event in the callback and hence cpu_online_mask can get
> updated in-between). But it would still work since cpus going down don't
> really pose problems for us.
Um? Sure, that loop can end up adding CPUs on their way down into the set.
And as soon as they get their CPU_DEAD, notifier will prune them out... Or
is there something I'm missing here? Anyway, the variant I have here
(untested) follows:
diff --git a/include/linux/lglock.h b/include/linux/lglock.h
index f549056..1951f67 100644
--- a/include/linux/lglock.h
+++ b/include/linux/lglock.h
@@ -22,6 +22,7 @@
#include <linux/spinlock.h>
#include <linux/lockdep.h>
#include <linux/percpu.h>
+#include <linux/cpu.h>
/* can make br locks by using local lock for read side, global lock for write */
#define br_lock_init(name) name##_lock_init()
@@ -72,9 +73,31 @@
#define DEFINE_LGLOCK(name) \
\
+ DEFINE_SPINLOCK(name##_cpu_lock); \
+ cpumask_t name##_cpus __read_mostly; \
DEFINE_PER_CPU(arch_spinlock_t, name##_lock); \
DEFINE_LGLOCK_LOCKDEP(name); \
\
+ static int \
+ name##_lg_cpu_callback(struct notifier_block *nb, \
+ unsigned long action, void *hcpu) \
+ { \
+ switch (action & ~CPU_TASKS_FROZEN) { \
+ case CPU_UP_PREPARE: \
+ spin_lock(&name##_cpu_lock); \
+ cpu_set((unsigned long)hcpu, name##_cpus); \
+ spin_unlock(&name##_cpu_lock); \
+ break; \
+ case CPU_UP_CANCELED: case CPU_DEAD: \
+ spin_lock(&name##_cpu_lock); \
+ cpu_clear((unsigned long)hcpu, name##_cpus); \
+ spin_unlock(&name##_cpu_lock); \
+ } \
+ return NOTIFY_OK; \
+ } \
+ static struct notifier_block name##_lg_cpu_notifier = { \
+ .notifier_call = name##_lg_cpu_callback, \
+ }; \
void name##_lock_init(void) { \
int i; \
LOCKDEP_INIT_MAP(&name##_lock_dep_map, #name, &name##_lock_key, 0); \
@@ -83,6 +106,11 @@
lock = &per_cpu(name##_lock, i); \
*lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; \
} \
+ register_hotcpu_notifier(&name##_lg_cpu_notifier); \
+ spin_lock(&name##_cpu_lock); \
+ for_each_online_cpu(i) \
+ cpu_set(i, name##_cpus); \
+ spin_unlock(&name##_cpu_lock); \
} \
EXPORT_SYMBOL(name##_lock_init); \
\
@@ -124,9 +152,9 @@
\
void name##_global_lock_online(void) { \
int i; \
- preempt_disable(); \
+ spin_lock(&name##_cpu_lock); \
rwlock_acquire(&name##_lock_dep_map, 0, 0, _RET_IP_); \
- for_each_online_cpu(i) { \
+ for_each_cpu(i, &name##_cpus) { \
arch_spinlock_t *lock; \
lock = &per_cpu(name##_lock, i); \
arch_spin_lock(lock); \
@@ -137,12 +165,12 @@
void name##_global_unlock_online(void) { \
int i; \
rwlock_release(&name##_lock_dep_map, 1, _RET_IP_); \
- for_each_online_cpu(i) { \
+ for_each_cpu(i, &name##_cpus) { \
arch_spinlock_t *lock; \
lock = &per_cpu(name##_lock, i); \
arch_spin_unlock(lock); \
} \
- preempt_enable(); \
+ spin_unlock(&name##_cpu_lock); \
} \
EXPORT_SYMBOL(name##_global_unlock_online); \
\
--
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