stop_machine: Don't disable preemption in stop_two_cpus()

Now that stop_two_cpus() path does not check cpu_active() we can remove
preempt_disable(), it was only needed to ensure that stop_machine() can
not be called after we observe cpu_active() == T and before we queue the
new work.

Also, turn the pointless and confusing ->executed check into WARN_ON().
We know that both works must be executed, otherwise we have a bug. And
in fact I think that done->executed should die, see the next changes.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Milos Vyletel <milos@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20151115193314.GA8249@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 8 deletions

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 1a66a9569915..17f01a9dc3df 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -258,7 +258,6 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
         struct cpu_stop_work work1, work2;
         struct multi_stop_data msdata;
 
-        preempt_disable();
         msdata = (struct multi_stop_data){
                 .fn = fn,
                 .data = arg,
@@ -277,16 +276,12 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
 
         if (cpu1 > cpu2)
                 swap(cpu1, cpu2);
-        if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2)) {
-                preempt_enable();
+        if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
                 return -ENOENT;
-        }
-
-        preempt_enable();
 
         wait_for_completion(&done.completion);
-
-        return done.executed ? done.ret : -ENOENT;
+        WARN_ON(!done.executed);
+        return done.ret;
 }
 
 /**