From baaca49f415b25fdbe2a8f3c22b39929e450fbfd Mon Sep 17 00:00:00 2001
From: Gautham R Shenoy <ego@in.ibm.com>
Date: Wed, 9 May 2007 02:34:03 -0700
Subject: [PATCH] Define and use new events,CPU_LOCK_ACQUIRE and
CPU_LOCK_RELEASE
This is an attempt to provide an alternate mechanism for postponing
a hotplug event instead of using a global mechanism like lock_cpu_hotplug.
The proposal is to add two new events namely CPU_LOCK_ACQUIRE and
CPU_LOCK_RELEASE. The notification for these two events would be sent
out before and after a cpu_hotplug event respectively.
During the CPU_LOCK_ACQUIRE event, a cpu-hotplug-aware subsystem is
supposed to acquire any per-subsystem hotcpu mutex ( Eg. workqueue_mutex
in kernel/workqueue.c ).
During the CPU_LOCK_RELEASE release event the cpu-hotplug-aware subsystem
is supposed to release the per-subsystem hotcpu mutex.
The reasons for defining new events as opposed to reusing the existing events
like CPU_UP_PREPARE/CPU_UP_FAILED/CPU_ONLINE for locking/unlocking of
per-subsystem hotcpu mutexes are as follow:
- CPU_LOCK_ACQUIRE: All hotcpu mutexes are taken before subsystems
start handling pre-hotplug events like CPU_UP_PREPARE/CPU_DOWN_PREPARE
etc, thus ensuring a clean handling of these events.
- CPU_LOCK_RELEASE: The hotcpu mutexes will be released only after
all subsystems have handled post-hotplug events like CPU_DOWN_FAILED,
CPU_DEAD,CPU_ONLINE etc thereby ensuring that there are no subsequent
clashes amongst the interdependent subsystems after a cpu hotplugs.
This patch also uses __raw_notifier_call chain in _cpu_up to take care
of the dependency between the two consequetive calls to
raw_notifier_call_chain.
[akpm@linux-foundation.org: fix a bug]
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
include/linux/notifier.h | 2 ++
kernel/cpu.c | 19 ++++++++++++++-----
2 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index e34221bf8946..1903e5490c04 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -194,6 +194,8 @@ extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
#define CPU_DOWN_PREPARE 0x0005 /* CPU (unsigned)v going down */
#define CPU_DOWN_FAILED 0x0006 /* CPU (unsigned)v NOT going down */
#define CPU_DEAD 0x0007 /* CPU (unsigned)v dead */
+#define CPU_LOCK_ACQUIRE 0x0008 /* Acquire all hotcpu locks */
+#define CPU_LOCK_RELEASE 0x0009 /* Release all hotcpu locks */
#endif /* __KERNEL__ */
#endif /* _LINUX_NOTIFIER_H */
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 36e70845cfc3..48810498b355 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -132,12 +132,15 @@ static int _cpu_down(unsigned int cpu)
if (!cpu_online(cpu))
return -EINVAL;
+ raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE,
+ (void *)(long)cpu);
err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
(void *)(long)cpu);
if (err == NOTIFY_BAD) {
printk("%s: attempt to take down CPU %u failed\n",
__FUNCTION__, cpu);
- return -EINVAL;
+ err = -EINVAL;
+ goto out_release;
}
/* Ensure that we are not runnable on dying cpu */
@@ -185,6 +188,9 @@ out_thread:
err = kthread_stop(p);
out_allowed:
set_cpus_allowed(current, old_allowed);
+out_release:
+ raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE,
+ (void *)(long)cpu);
return err;
}
@@ -206,13 +212,15 @@ int cpu_down(unsigned int cpu)
/* Requires cpu_add_remove_lock to be held */
static int __cpuinit _cpu_up(unsigned int cpu)
{
- int ret;
+ int ret, nr_calls = 0;
void *hcpu = (void *)(long)cpu;
if (cpu_online(cpu) || !cpu_present(cpu))
return -EINVAL;
- ret = raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
+ raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
+ ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu,
+ -1, &nr_calls);
if (ret == NOTIFY_BAD) {
printk("%s: attempt to bring up CPU %u failed\n",
__FUNCTION__, cpu);
@@ -233,8 +241,9 @@ static int __cpuinit _cpu_up(unsigned int cpu)
out_notify:
if (ret != 0)
- raw_notifier_call_chain(&cpu_chain,
- CPU_UP_CANCELED, hcpu);
+ __raw_notifier_call_chain(&cpu_chain,
+ CPU_UP_CANCELED, hcpu, nr_calls, NULL);
+ raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
return ret;
}
--
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