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/kernel/module.c b/kernel/module.c
index 1016b75b026a..0838246d8c94 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -723,16 +723,8 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
                 return -EFAULT;
         name[MODULE_NAME_LEN-1] = '\0';
 
-        /* Create stop_machine threads since free_module relies on
-         * a non-failing stop_machine call. */
-        ret = stop_machine_create();
-        if (ret)
-                return ret;
-
-        if (mutex_lock_interruptible(&module_mutex) != 0) {
-                ret = -EINTR;
-                goto out_stop;
-        }
+        if (mutex_lock_interruptible(&module_mutex) != 0)
+                return -EINTR;
 
         mod = find_module(name);
         if (!mod) {
@@ -792,8 +784,6 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
 
  out:
         mutex_unlock(&module_mutex);
-out_stop:
-        stop_machine_destroy();
         return ret;
 }