stop_machine: reimplement using cpu_stop

Reimplement stop_machine using cpu_stop.  As cpu stoppers are
guaranteed to be available for all online cpus,
stop_machine_create/destroy() are no longer necessary and removed.

With resource management and synchronization handled by cpu_stop, the
new implementation is much simpler.  Asking the cpu_stop to execute
the stop_cpu() state machine on all online cpus with cpu hotplug
disabled is enough.

stop_machine itself doesn't need to manage any global resources
anymore, so all per-instance information is rolled into struct
stop_machine_data and the mutex and all static data variables are
removed.

The previous implementation created and destroyed RT workqueues as
necessary which made stop_machine() calls highly expensive on very
large machines.  According to Dimitri Sivanich, preventing the dynamic
creation/destruction makes booting faster more than twice on very
large machines.  cpu_stop resources are preallocated for all online
cpus and should have the same effect.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>

1 files changed, 2 insertions, 12 deletions

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index 2ac4440e7b08..8943b8ccee1a 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -80,12 +80,6 @@ static void do_suspend(void)
 
         shutting_down = SHUTDOWN_SUSPEND;
 
-        err = stop_machine_create();
-        if (err) {
-                printk(KERN_ERR "xen suspend: failed to setup stop_machine %d\n", err);
-                goto out;
-        }
-
 #ifdef CONFIG_PREEMPT
         /* If the kernel is preemptible, we need to freeze all the processes
            to prevent them from being in the middle of a pagetable update
@@ -93,7 +87,7 @@ static void do_suspend(void)
         err = freeze_processes();
         if (err) {
                 printk(KERN_ERR "xen suspend: freeze failed %d\n", err);
-                goto out_destroy_sm;
+                goto out;
         }
 #endif
 
@@ -136,12 +130,8 @@ out_resume:
 out_thaw:
 #ifdef CONFIG_PREEMPT
         thaw_processes();
-
-out_destroy_sm:
-#endif
-        stop_machine_destroy();
-
 out:
+#endif
         shutting_down = SHUTDOWN_INVALID;
 }
 #endif  /* CONFIG_PM_SLEEP */