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Commit baaca49f authored by Gautham R Shenoy's avatar Gautham R Shenoy Committed by Linus Torvalds
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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: default avatarGautham R Shenoy <ego@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6f7cc11a

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 @@ static int _cpu_down(unsigned int cpu) 
	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;

}