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Date: Fri, 26 Jun 2015 15:27:34 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: devel@...uxdriverproject.org
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
linux-kernel@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
Ingo Molnar <mingo@...nel.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Radim Krčmář <rkrcmar@...hat.com>
Subject: [PATCH v6 3/3] cpu-hotplug: convert cpu_hotplug_disabled to a counter
As cpu_hotplug_enable/cpu_hotplug_disable functions are now available 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 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: Vitaly Kuznetsov <vkuznets@...hat.com>
---
Documentation/power/suspend-and-cpuhotplug.txt | 6 +++---
kernel/cpu.c | 21 +++++++++++++--------
2 files changed, 16 insertions(+), 11 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 dc005e7..cab3c92 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -190,7 +190,7 @@ 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);
@@ -198,7 +198,7 @@ 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);
@@ -598,13 +598,18 @@ 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;
}
@@ -623,7 +628,7 @@ 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;
--
2.4.3
--
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