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 <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Tested-by: Paul E. McKenney <[email protected]> Acked-by: Paul E. McKenney <[email protected]> Acked-by: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Steven Rostedt <[email protected]> Link: http://lkml.kernel.org/r/[email protected]
Rust-for-Linux · May 26, 2017 · fe5595c · fe5595c
1 parent 9805c67
commit fe5595c
Show file tree

Hide file tree

Showing 2 changed files with 30 additions and 7 deletions.
diff --git 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 cpus_read_lock() protected
+ * region. Avoids nested calls to cpus_read_lock().
+ */
+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
@@ -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,
@@ -561,6 +562,8 @@ static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cp
 		.active_cpus = cpus,
 	};
 
+	lockdep_assert_cpus_held();
+
 	if (!stop_machine_initialized) {
 		/*
 		 * Handle the case where stop_machine() is called
@@ -590,9 +593,9 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
 	int ret;
 
 	/* No CPUs can come up or down during this. */
-	get_online_cpus();
-	ret = __stop_machine(fn, data, cpus);
-	put_online_cpus();
+	cpus_read_lock();
+	ret = stop_machine_cpuslocked(fn, data, cpus);
+	cpus_read_unlock();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(stop_machine);