stop_machine: Provide stop_machine_cpuslocked()

Some call sites of stop_machine() are within a get_online_cpus() protected
region.

stop_machine() calls get_online_cpus() as well, which is possible in the
current implementation but prevents converting the hotplug locking to a
percpu rwsem.

Provide stop_machine_cpuslocked() to avoid nested calls to get_online_cpus().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170524081547.400700852@linutronix.de

1 files changed, 7 insertions, 4 deletions

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 1eb82661ecdb..b7591261652d 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -552,7 +552,8 @@ static int __init cpu_stop_init(void)
 }
 early_initcall(cpu_stop_init);
 
-static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
+int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
+                            const struct cpumask *cpus)
 {
         struct multi_stop_data msdata = {
                 .fn = fn,
@@ -561,6 +562,8 @@ static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cp
                 .active_cpus = cpus,
         };
 
+        lockdep_assert_cpus_held();
+
         if (!stop_machine_initialized) {
                 /*
                  * Handle the case where stop_machine() is called
@@ -590,9 +593,9 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
         int ret;
 
         /* No CPUs can come up or down during this. */
-        get_online_cpus();
-        ret = __stop_machine(fn, data, cpus);
-        put_online_cpus();
+        cpus_read_lock();
+        ret = stop_machine_cpuslocked(fn, data, cpus);
+        cpus_read_unlock();
         return ret;
 }
 EXPORT_SYMBOL_GPL(stop_machine);