stop_machine: add ALL_CPUS option

-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>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
CC: Adrian Bunk <bunk@stusta.de>
CC: Andi Kleen <andi@firstfloor.org>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Christoph Hellwig <hch@infradead.org>
CC: mingo@elte.hu
CC: akpm@osdl.org

diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 5bfc553..18af011 100644 (file)
--- 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 738b411..a473bd0 100644 (file)
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -22,9 +22,17 @@ 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;
@@ -33,6 +41,7 @@ static int stopmachine(void *cpu)
 {
        int irqs_disabled = 0;
        int prepared = 0;
+       int ran = 0;
        cpumask_of_cpu_ptr(cpumask, (int)(long)cpu);
 
        set_cpus_allowed_ptr(current, cpumask);
@@ -58,6 +67,11 @@ 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. */
@@ -136,11 +150,10 @@ static void restart_machine(void)
        preempt_enable_no_resched();
 }
 
-struct stop_machine_data {
-       int (*fn)(void *);
-       void *data;
-       struct completion done;
-};
+static void run_other_cpus(void)
+{
+       stopmachine_set_state(STOPMACHINE_RUN);
+}
 
 static int do_stop(void *_smdata)
 {
@@ -150,6 +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();
        }
 
@@ -173,14 +188,17 @@ struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
        struct stop_machine_data smdata;
        struct task_struct *p;
 
+       mutex_lock(&stopmachine_mutex);
+
        smdata.fn = fn;
        smdata.data = data;
+       smdata.run_all = (cpu == ALL_CPUS) ? 1 : 0;
        init_completion(&smdata.done);
 
-       mutex_lock(&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");