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Subject[patch 1/2] add ALL_CPUS option to stop_machine_run()

-allow stop_mahcine_run() to call a function on all cpus. Calling
stop_machine_run() with a 'ALL_CPUS' invokes this new behavior.
stop_machine_run() proceeds as normal until the calling cpu has
invoked 'fn'. Then, we tell all the other cpus to call 'fn'.

Signed-off-by: Jason Baron <jbaron@redhat.com>


---

include/linux/stop_machine.h | 8 +++++++-
kernel/stop_machine.c | 33 +++++++++++++++++++++++----------
2 files changed, 30 insertions(+), 11 deletions(-)


diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 5bfc553..18af011 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -8,11 +8,17 @@
#include <asm/system.h>

#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
+
+#define ALL_CPUS ~0U
+
/**
* 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.
+ * @cpu: if @cpu == n, run @fn() on cpu n
+ * if @cpu == NR_CPUS, run @fn() on any cpu
+ * if @cpu == ALL_CPUS, run @fn() first on the calling cpu, and then
+ * concurrently on all the other cpus
*
* Description: This causes a thread to be scheduled on every other cpu,
* each of which disables interrupts, and finally interrupts are disabled
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 51b5ee5..c75b4f4 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -23,9 +23,17 @@ enum stopmachine_state {
STOPMACHINE_WAIT,
STOPMACHINE_PREPARE,
STOPMACHINE_DISABLE_IRQ,
+ STOPMACHINE_RUN,
STOPMACHINE_EXIT,
};

+struct stop_machine_data {
+ int (*fn)(void *);
+ void *data;
+ struct completion done;
+ int run_all;
+} smdata;
+
static enum stopmachine_state stopmachine_state;
static unsigned int stopmachine_num_threads;
static atomic_t stopmachine_thread_ack;
@@ -35,6 +43,7 @@ static int stopmachine(void *cpu)
{
int irqs_disabled = 0;
int prepared = 0;
+ int ran = 0;

set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));

@@ -59,6 +68,11 @@ static int stopmachine(void *cpu)
prepared = 1;
smp_mb(); /* Must read state first. */
atomic_inc(&stopmachine_thread_ack);
+ } else if (stopmachine_state == STOPMACHINE_RUN && !ran) {
+ smdata.fn(smdata.data);
+ ran = 1;
+ smp_mb(); /* Must read state first. */
+ atomic_inc(&stopmachine_thread_ack);
}
/* Yield in first stage: migration threads need to
* help our sisters onto their CPUs. */
@@ -136,12 +150,10 @@ static void restart_machine(void)
preempt_enable_no_resched();
}

-struct stop_machine_data
+static void run_other_cpus(void)
{
- int (*fn)(void *);
- void *data;
- struct completion done;
-};
+ stopmachine_set_state(STOPMACHINE_RUN);
+}

static int do_stop(void *_smdata)
{
@@ -151,6 +163,8 @@ static int do_stop(void *_smdata)
ret = stop_machine();
if (ret == 0) {
ret = smdata->fn(smdata->data);
+ if (smdata->run_all)
+ run_other_cpus();
restart_machine();
}

@@ -170,17 +184,16 @@ static int do_stop(void *_smdata)
struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
unsigned int cpu)
{
- struct stop_machine_data smdata;
struct task_struct *p;

+ down(&stopmachine_mutex);
smdata.fn = fn;
smdata.data = data;
+ smdata.run_all = (cpu == ALL_CPUS) ? 1 : 0;
init_completion(&smdata.done);
-
- down(&stopmachine_mutex);
-
+ smp_wmb(); /* make sure other cpus see smdata updates */
/* If they don't care which CPU fn runs on, bind to any online one. */
- if (cpu == NR_CPUS)
+ if (cpu == NR_CPUS || cpu == ALL_CPUS)
cpu = raw_smp_processor_id();

p = kthread_create(do_stop, &smdata, "kstopmachine");


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