stop_machine(): stop_machine_run() changed to use cpu mask

Instead of a "cpu" arg with magic values NR_CPUS (any cpu) and ~0 (all
cpus), pass a cpumask_t.  Allow NULL for the common case (where we
don't care which CPU the function is run on): temporary cpumask_t's
are usually considered bad for stack space.

This deprecates stop_machine_run, to be removed soon when all the
callers are dead.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

include/linux/stop_machine.h

@@ -5,19 +5,19 @@
    (and more).  So the "read" side to such a lock is anything which
    diables preeempt. */
 #include <linux/cpu.h>
+#include <linux/cpumask.h>
 #include <asm/system.h>
 
 #if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
 
+/* Deprecated, but useful for transition. */
 #define ALL_CPUS ~0U
 
 /**
- * stop_machine_run: freeze the machine on all CPUs and run this function
+ * stop_machine: freeze the machine on all CPUs and run this function
  * @fn: the function to run
  * @data: the data ptr for the @fn()
- * @cpu: if @cpu == n, run @fn() on cpu n
- *       if @cpu == NR_CPUS, run @fn() on any cpu
- *       if @cpu == ALL_CPUS, run @fn() on every online CPU.
+ * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
  *
  * Description: This causes a thread to be scheduled on every cpu,
  * each of which disables interrupts.  The result is that noone is
@@ -26,22 +26,22 @@
  *
  * This can be thought of as a very heavy write lock, equivalent to
  * grabbing every spinlock in the kernel. */
-int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu);
+int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus);
 
 /**
- * __stop_machine_run: freeze the machine on all CPUs and run this function
+ * __stop_machine: freeze the machine on all CPUs and run this function
  * @fn: the function to run
  * @data: the data ptr for the @fn
- * @cpu: the cpu to run @fn on (or any, if @cpu == NR_CPUS.
+ * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
  *
  * Description: This is a special version of the above, which assumes cpus
  * won't come or go while it's being called.  Used by hotplug cpu.
  */
-int __stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu);
+int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus);
 #else
 
-static inline int stop_machine_run(int (*fn)(void *), void *data,
-				   unsigned int cpu)
+static inline int stop_machine(int (*fn)(void *), void *data,
+			       const cpumask_t *cpus)
 {
 	int ret;
 	local_irq_disable();
@@ -50,4 +50,18 @@ static inline int stop_machine_run(int (*fn)(void *), void *data,
 	return ret;
 }
 #endif /* CONFIG_SMP */
+
+static inline int __deprecated stop_machine_run(int (*fn)(void *), void *data,
+						unsigned int cpu)
+{
+	/* If they don't care which cpu fn runs on, just pick one. */
+	if (cpu == NR_CPUS)
+		return stop_machine(fn, data, NULL);
+	else if (cpu == ~0U)
+		return stop_machine(fn, data, &cpu_possible_map);
+	else {
+		cpumask_t cpus = cpumask_of_cpu(cpu);
+		return stop_machine(fn, data, &cpus);
+	}
+}
 #endif /* _LINUX_STOP_MACHINE */

kernel/cpu.c

@@ -248,8 +248,9 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 	cpus_setall(tmp);
 	cpu_clear(cpu, tmp);
 	set_cpus_allowed_ptr(current, &tmp);
+	tmp = cpumask_of_cpu(cpu);
 
-	err = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
+	err = __stop_machine(take_cpu_down, &tcd_param, &tmp);
 	if (err) {
 		/* CPU didn't die: tell everyone.  Can't complain. */
 		if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,

kernel/stop_machine.c

@@ -100,7 +100,7 @@ static int chill(void *unused)
 	return 0;
 }
 
-int __stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
+int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
 {
 	int i, err;
 	struct stop_machine_data active, idle;
@@ -112,10 +112,6 @@ int __stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 	idle.fn = chill;
 	idle.data = NULL;
 
-	/* If they don't care which cpu fn runs on, just pick one. */
-	if (cpu == NR_CPUS)
-		cpu = any_online_cpu(cpu_online_map);
-
 	/* This could be too big for stack on large machines. */
 	threads = kcalloc(NR_CPUS, sizeof(threads[0]), GFP_KERNEL);
 	if (!threads)
@@ -128,13 +124,16 @@ int __stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 	set_state(STOPMACHINE_PREPARE);
 
 	for_each_online_cpu(i) {
-		struct stop_machine_data *smdata;
+		struct stop_machine_data *smdata = &idle;
 		struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 
-		if (cpu == ALL_CPUS || i == cpu)
-			smdata = &active;
-		else
-			smdata = &idle;
+		if (!cpus) {
+			if (i == first_cpu(cpu_online_map))
+				smdata = &active;
+		} else {
+			if (cpu_isset(i, *cpus))
+				smdata = &active;
+		}
 
 		threads[i] = kthread_create((void *)stop_cpu, smdata, "kstop%u",
 					    i);
@@ -154,7 +153,7 @@ int __stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 
 	/* We've created all the threads.  Wake them all: hold this CPU so one
 	 * doesn't hit this CPU until we're ready. */
-	cpu = get_cpu();
+	get_cpu();
 	for_each_online_cpu(i)
 		wake_up_process(threads[i]);
 
@@ -177,15 +176,15 @@ int __stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
 	return err;
 }
 
-int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
+int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
 {
 	int ret;
 
 	/* No CPUs can come up or down during this. */
 	get_online_cpus();
-	ret = __stop_machine_run(fn, data, cpu);
+	ret = __stop_machine(fn, data, cpus);
 	put_online_cpus();
 
 	return ret;
 }
-EXPORT_SYMBOL_GPL(stop_machine_run);
+EXPORT_SYMBOL_GPL(stop_machine);