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Subject[tip:smp/hotplug] stop_machine: Provide stop_machine_cpuslocked()
Commit-ID:  e878ce0f69caa5c37f3183af711291c0c6a38d6a
Gitweb: http://git.kernel.org/tip/e878ce0f69caa5c37f3183af711291c0c6a38d6a
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Tue, 18 Apr 2017 19:04:44 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 20 Apr 2017 13:08:50 +0200

stop_machine: Provide stop_machine_cpuslocked()

Some call sites of stop_machine() are within a get_online_cpus() protected
region.

stop_machine() calls get_online_cpus() as well, which is possible in the
current implementation but prevents converting the hotplug locking to a
percpu rwsem.

Provide stop_machine_cpuslocked() to avoid nested calls to get_online_cpus().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170418170552.526243990@linutronix.de
---
include/linux/stop_machine.h | 26 +++++++++++++++++++++++---
kernel/stop_machine.c | 5 +++--
2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 3cc9632..8a068bd 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -116,15 +116,29 @@ static inline int try_stop_cpus(const struct cpumask *cpumask,
* @fn() runs.
*
* This can be thought of as a very heavy write lock, equivalent to
- * grabbing every spinlock in the kernel. */
+ * grabbing every spinlock in the kernel.
+ *
+ * Protects against CPU hotplug.
+ */
int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);

+/**
+ * stop_machine_cpuslocked: freeze the machine on all CPUs and run this function
+ * @fn: the function to run
+ * @data: the data ptr for the @fn()
+ * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
+ *
+ * Same as above. Must be called from with in a get_online_cpus() protected
+ * region. Avoids nested calls to get_online_cpus().
+ */
+int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
+
int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
const struct cpumask *cpus);
#else /* CONFIG_SMP || CONFIG_HOTPLUG_CPU */

-static inline int stop_machine(cpu_stop_fn_t fn, void *data,
- const struct cpumask *cpus)
+static inline int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
+ const struct cpumask *cpus)
{
unsigned long flags;
int ret;
@@ -134,6 +148,12 @@ static inline int stop_machine(cpu_stop_fn_t fn, void *data,
return ret;
}

+static inline int stop_machine(cpu_stop_fn_t fn, void *data,
+ const struct cpumask *cpus)
+{
+ return stop_machine_cpuslocked(fn, data, cpus);
+}
+
static inline int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
const struct cpumask *cpus)
{
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 1eb8266..a8c5636 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -552,7 +552,8 @@ static int __init cpu_stop_init(void)
}
early_initcall(cpu_stop_init);

-static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
+int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
+ const struct cpumask *cpus)
{
struct multi_stop_data msdata = {
.fn = fn,
@@ -591,7 +592,7 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)

/* No CPUs can come up or down during this. */
get_online_cpus();
- ret = __stop_machine(fn, data, cpus);
+ ret = stop_machine_cpuslocked(fn, data, cpus);
put_online_cpus();
return ret;
}
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