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Subject[PATCH 3/3] stop_machine: use cpu mask rather than magic numbers
Date
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.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r 277c5fb41d25 arch/s390/kernel/kprobes.c
--- a/arch/s390/kernel/kprobes.c Tue Jul 08 12:57:33 2008 +1000
+++ b/arch/s390/kernel/kprobes.c Tue Jul 08 17:31:41 2008 +1000
@@ -199,7 +199,7 @@ void __kprobes arch_arm_kprobe(struct kp
args.new = BREAKPOINT_INSTRUCTION;

kcb->kprobe_status = KPROBE_SWAP_INST;
- stop_machine_run(swap_instruction, &args, NR_CPUS);
+ stop_machine_run(swap_instruction, &args, NULL);
kcb->kprobe_status = status;
}

@@ -214,7 +214,7 @@ void __kprobes arch_disarm_kprobe(struct
args.new = p->opcode;

kcb->kprobe_status = KPROBE_SWAP_INST;
- stop_machine_run(swap_instruction, &args, NR_CPUS);
+ stop_machine_run(swap_instruction, &args, NULL);
kcb->kprobe_status = status;
}

diff -r 277c5fb41d25 drivers/char/hw_random/intel-rng.c
--- a/drivers/char/hw_random/intel-rng.c Tue Jul 08 12:57:33 2008 +1000
+++ b/drivers/char/hw_random/intel-rng.c Tue Jul 08 17:31:41 2008 +1000
@@ -368,7 +368,7 @@ static int __init mod_init(void)
* Use stop_machine_run because IPIs can be blocked by disabling
* interrupts.
*/
- err = stop_machine_run(intel_rng_hw_init, intel_rng_hw, NR_CPUS);
+ err = stop_machine_run(intel_rng_hw_init, intel_rng_hw, NULL);
pci_dev_put(dev);
iounmap(intel_rng_hw->mem);
kfree(intel_rng_hw);
diff -r 277c5fb41d25 include/linux/stop_machine.h
--- a/include/linux/stop_machine.h Tue Jul 08 12:57:33 2008 +1000
+++ b/include/linux/stop_machine.h Tue Jul 08 17:31:41 2008 +1000
@@ -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)

-#define ALL_CPUS ~0U
+/* Deprecated, but useful for transition. */
+#define ALL_CPUS CPU_MASK_ALL_PTR

/**
* stop_machine_run: 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_run(int (*fn)(void *), void *data, const cpumask_t *cpus);

/**
* __stop_machine_run: 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_run(int (*fn)(void *), void *data, const cpumask_t *cpus);
#else

static inline int stop_machine_run(int (*fn)(void *), void *data,
- unsigned int cpu)
+ const cpumask_t *cpus)
{
int ret;
local_irq_disable();
diff -r 277c5fb41d25 kernel/cpu.c
--- a/kernel/cpu.c Tue Jul 08 12:57:33 2008 +1000
+++ b/kernel/cpu.c Tue Jul 08 17:31:41 2008 +1000
@@ -224,8 +224,9 @@ static int __ref _cpu_down(unsigned int
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_run(take_cpu_down, &tcd_param, &tmp);

if (err || cpu_online(cpu)) {
/* CPU didn't die: tell everyone. Can't complain. */
diff -r 277c5fb41d25 kernel/module.c
--- a/kernel/module.c Tue Jul 08 12:57:33 2008 +1000
+++ b/kernel/module.c Tue Jul 08 17:31:41 2008 +1000
@@ -689,7 +689,7 @@ static int try_stop_module(struct module
{
struct stopref sref = { mod, flags, forced };

- return stop_machine_run(__try_stop_module, &sref, NR_CPUS);
+ return stop_machine_run(__try_stop_module, &sref, NULL);
}

unsigned int module_refcount(struct module *mod)
@@ -1421,7 +1421,7 @@ static void free_module(struct module *m
static void free_module(struct module *mod)
{
/* Delete from various lists */
- stop_machine_run(__unlink_module, mod, NR_CPUS);
+ stop_machine_run(__unlink_module, mod, NULL);
remove_notes_attrs(mod);
remove_sect_attrs(mod);
mod_kobject_remove(mod);
@@ -2189,7 +2189,7 @@ static struct module *load_module(void _
/* Now sew it into the lists so we can get lockdep and oops
* info during argument parsing. Noone should access us, since
* strong_try_module_get() will fail. */
- stop_machine_run(__link_module, mod, NR_CPUS);
+ stop_machine_run(__link_module, mod, NULL);

/* Size of section 0 is 0, so this works well if no params */
err = parse_args(mod->name, mod->args,
@@ -2223,7 +2223,7 @@ static struct module *load_module(void _
return mod;

unlink:
- stop_machine_run(__unlink_module, mod, NR_CPUS);
+ stop_machine_run(__unlink_module, mod, NULL);
module_arch_cleanup(mod);
cleanup:
kobject_del(&mod->mkobj.kobj);
diff -r 277c5fb41d25 kernel/stop_machine.c
--- a/kernel/stop_machine.c Tue Jul 08 12:57:33 2008 +1000
+++ b/kernel/stop_machine.c Tue Jul 08 17:31:41 2008 +1000
@@ -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_run(int (*fn)(void *), void *data, const cpumask_t *cpus)
{
int i, err;
struct stop_machine_data active, idle;
@@ -111,10 +111,6 @@ int __stop_machine_run(int (*fn)(void *)
active.fnret = 0;
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);
@@ -128,13 +124,16 @@ int __stop_machine_run(int (*fn)(void *)
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(stop_cpu, smdata, "kstop%u", i);
if (IS_ERR(threads[i])) {
@@ -153,7 +152,7 @@ int __stop_machine_run(int (*fn)(void *)

/* 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]);

@@ -176,13 +175,13 @@ kill_threads:
return err;
}

-int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
+int stop_machine_run(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_run(fn, data, cpus);
put_online_cpus();

return ret;
diff -r 277c5fb41d25 mm/page_alloc.c
--- a/mm/page_alloc.c Tue Jul 08 12:57:33 2008 +1000
+++ b/mm/page_alloc.c Tue Jul 08 17:31:41 2008 +1000
@@ -2356,7 +2356,7 @@ void build_all_zonelists(void)
} else {
/* we have to stop all cpus to guarantee there is no user
of zonelist */
- stop_machine_run(__build_all_zonelists, NULL, NR_CPUS);
+ stop_machine_run(__build_all_zonelists, NULL, NULL);
/* cpuset refresh routine should be here */
}
vm_total_pages = nr_free_pagecache_pages();

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