Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> writes:
> Loaded Hyper-V module will use these functions to disable CPU hotplug
> under certain circumstances. Convert cpu_hotplug_disabled to a counter
> (protected by cpu_add_remove_lock) to support e.g. disable -> disable ->
> enable call sequences.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
> Documentation/power/suspend-and-cpuhotplug.txt | 6 +++---
> kernel/cpu.c | 11 ++++++-----
> 2 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/power/suspend-and-cpuhotplug.txt b/Documentation/power/suspend-and-cpuhotplug.txt
> index 2850df3..2fc9095 100644
> --- a/Documentation/power/suspend-and-cpuhotplug.txt
> +++ b/Documentation/power/suspend-and-cpuhotplug.txt
> @@ -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
> |
> |
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 94bbe46..b6e42d2 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -190,17 +190,18 @@ 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();
> }
> +EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
>
> void cpu_hotplug_enable(void)
> {
> cpu_maps_update_begin();
> - cpu_hotplug_disabled = 0;
> + WARN_ON(--cpu_hotplug_disabled < 0);
> cpu_maps_update_done();
> }
> -
> +EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
> #endif /* CONFIG_HOTPLUG_CPU */
>
> /* Need to know about CPUs going up/down? */
> @@ -600,7 +601,7 @@ int disable_nonboot_cpus(void)
> if (!error) {
> BUG_ON(num_online_cpus() > 1);
> /* Make sure the CPUs won't be enabled by someone else */
> - cpu_hotplug_disabled = 1;
> + cpu_hotplug_disabled++;
Actually, there is an issue here: all disable_nonboot_cpus() users do
enable_nonboot_cpus() in case of failure (yesterday I sent a patch to
fix the last one: https://lkml.org/lkml/2015/6/24/379) but we do
cpu_hotplug_disabled++ only in case of success. I think we need to do
cpu_hotplug_disabled++ here unconditionally.
I'll fix and resend.
> } else {
> pr_err("Non-boot CPUs are not disabled\n");
> }
> @@ -622,7 +623,7 @@ 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);
(here we don't really know if we had a success or a failure in
previously called disable_nonboot_cpus()).
> if (cpumask_empty(frozen_cpus))
> goto out;
--
Vitaly
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