From baaca49f415b25fdbe2a8f3c22b39929e450fbfd Mon Sep 17 00:00:00 2001 From: Gautham R Shenoy 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 e34221bf894..1903e5490c0 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 36e70845cfc..48810498b35 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; }