coredump: turn core_state->nr_threads into atomic_t

Turn core_state->nr_threads into atomic_t and kill now unneeded
down_write(&mm->mmap_sem) in exit_mm().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 988e232254e..63d82957baa 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -678,10 +678,9 @@ static void exit_mm(struct task_struct * tsk)
         down_read(&mm->mmap_sem);
         if (mm->core_state) {
                 up_read(&mm->mmap_sem);
-                down_write(&mm->mmap_sem);
-                if (!--mm->core_state->nr_threads)
+
+                if (atomic_dec_and_test(&mm->core_state->nr_threads))
                         complete(&mm->core_state->startup);
-                up_write(&mm->mmap_sem);
 
                 wait_for_completion(&mm->core_done);
                 down_read(&mm->mmap_sem);