Commit 89af7ba5 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Greg Kroah-Hartman
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cpu-hotplug: convert cpu_hotplug_disabled to a counter 



As a prerequisite to exporting cpu_hotplug_enable/cpu_hotplug_disable
functions to modules we need to convert cpu_hotplug_disabled to a counter
to properly support disable -> disable -> enable call sequences. E.g.
after Hyper-V vmbus module (which is supposed to be the first user of
exported cpu_hotplug_enable/cpu_hotplug_disable) did cpu_hotplug_disable()
hibernate path calls disable_nonboot_cpus() and if we hit an error in
_cpu_down() enable_nonboot_cpus() will be called on the failure path (thus
making cpu_hotplug_disabled = 0 and leaving cpu hotplug in 'enabled'
state). Same problem is possible if more than 1 module use
cpu_hotplug_disable/cpu_hotplug_enable on their load/unload paths. When
one of these modules is been unloaded it is logical to leave cpu hotplug
in 'disabled' state.

To support the change we need to increse cpu_hotplug_disabled counter
in disable_nonboot_cpus() unconditionally as all users of
disable_nonboot_cpus() are supposed to do enable_nonboot_cpus() in case
an error was returned.

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 54bf725e

Documentation/power/suspend-and-cpuhotplug.txt

+3 −3
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ More details follow: 
                                        |

                                        v

                           Disable regular cpu hotplug

                        by setting cpu_hotplug_disabled=1

                        by increasing cpu_hotplug_disabled

                                        |

                                        v

                            Release cpu_add_remove_lock
@@ -89,7 +89,7 @@ Resuming back is likewise, with the counterparts being (in the order of 
execution during resume):

* enable_nonboot_cpus() which involves:

   |  Acquire cpu_add_remove_lock

   |  Reset cpu_hotplug_disabled to 0, thereby enabling regular cpu hotplug

   |  Decrease cpu_hotplug_disabled, thereby enabling regular cpu hotplug

   |  Call _cpu_up() [for all those cpus in the frozen_cpus mask, in a loop]

   |  Release cpu_add_remove_lock

   v
@@ -120,7 +120,7 @@ after the entire cycle is complete (i.e., suspend + resume). 
                           Acquire cpu_add_remove_lock

                                        |

                                        v

                          If cpu_hotplug_disabled is 1

                          If cpu_hotplug_disabled > 0

                                return gracefully

                                        |

                                        |

kernel/cpu.c

+13 −8
Original line number Diff line number Diff line
@@ -191,14 +191,14 @@ void cpu_hotplug_done(void) 
void cpu_hotplug_disable(void)

{

	cpu_maps_update_begin();

	cpu_hotplug_disabled = 1;

	cpu_hotplug_disabled++;

	cpu_maps_update_done();

}



void cpu_hotplug_enable(void)

{

	cpu_maps_update_begin();

	cpu_hotplug_disabled = 0;

	WARN_ON(--cpu_hotplug_disabled < 0);

	cpu_maps_update_done();

}
@@ -608,13 +608,18 @@ int disable_nonboot_cpus(void) 
		}

	}



	if (!error) {

	if (!error)

		BUG_ON(num_online_cpus() > 1);

		/* Make sure the CPUs won't be enabled by someone else */

		cpu_hotplug_disabled = 1;

	} else {

	else

		pr_err("Non-boot CPUs are not disabled\n");

	}



	/*

	 * Make sure the CPUs won't be enabled by someone else. We need to do

	 * this even in case of failure as all disable_nonboot_cpus() users are

	 * supposed to do enable_nonboot_cpus() on the failure path.

	 */

	cpu_hotplug_disabled++;



	cpu_maps_update_done();

	return error;

}
@@ -633,7 +638,7 @@ void __ref enable_nonboot_cpus(void) 


	/* Allow everyone to use the CPU hotplug again */

	cpu_maps_update_begin();

	cpu_hotplug_disabled = 0;

	WARN_ON(--cpu_hotplug_disabled < 0);

	if (cpumask_empty(frozen_cpus))

		goto out;

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