Define and use new events,CPU_LOCK_ACQUIRE and CPU_LOCK_RELEASE (baaca49f) · Commits · 戴 / test

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 −0

Original line number	Diff line number	Diff line
		@@ -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 */

kernel/cpu.c

+14 −5

Original line number	Diff line number	Diff line
		@@ -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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