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x86, oprofile, nmi: Fix CPU hotplug callback registration

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Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();

Fix the oprofile code in x86 by using this latter form of callback
registration. But retain the calls to get/put_online_cpus(), since they are
used in other places as well, to protect the variables 'nmi_enabled' and
'ctr_running'. Strictly speaking, this is not necessary since
cpu_notifier_register_begin/done() provide a stronger synchronization
with CPU hotplug than get/put_online_cpus(). However, let's retain the
calls to get/put_online_cpus() to be consistent with the other call-sites.

By nesting get/put_online_cpus() *inside* cpu_notifier_register_begin/done(),
we avoid the ABBA deadlock possibility mentioned above.

Cc: Robert Richter <rric@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Srivatsa S. Bhat 2014-03-11 02:08:49 +05:30 committed by Rafael J. Wysocki
parent 9f668f6661
commit 76902e3d9c
1 changed files with 13 additions and 2 deletions
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15
arch/x86/oprofile/nmi_int.c
View File

@ -494,14 +494,19 @@ static int nmi_setup(void)
if (err)
goto fail;
cpu_notifier_register_begin();
/* Use get/put_online_cpus() to protect 'nmi_enabled' */
get_online_cpus();
register_cpu_notifier(&oprofile_cpu_nb);
nmi_enabled = 1;
/* make nmi_enabled visible to the nmi handler: */
smp_mb();
on_each_cpu(nmi_cpu_setup, NULL, 1);
__register_cpu_notifier(&oprofile_cpu_nb);
put_online_cpus();
cpu_notifier_register_done();
return 0;
fail:
free_msrs();
@ -512,12 +517,18 @@ static void nmi_shutdown(void)
{
struct op_msrs *msrs;
cpu_notifier_register_begin();
/* Use get/put_online_cpus() to protect 'nmi_enabled' & 'ctr_running' */
get_online_cpus();
unregister_cpu_notifier(&oprofile_cpu_nb);
on_each_cpu(nmi_cpu_shutdown, NULL, 1);
nmi_enabled = 0;
ctr_running = 0;
__unregister_cpu_notifier(&oprofile_cpu_nb);
put_online_cpus();
cpu_notifier_register_done();
/* make variables visible to the nmi handler: */
smp_mb();
unregister_nmi_handler(NMI_LOCAL, "oprofile");