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>

3 files changed, 4 insertions, 5 deletions

diff --git a/fs/exec.c b/fs/exec.c
index c74bb34eeeff..15d493fe8aa3 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1591,7 +1591,7 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
         }
         rcu_read_unlock();
 done:
-        core_state->nr_threads = nr;
+        atomic_set(&core_state->nr_threads, nr);
         return nr;
 }
 
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c0b1747b61a5..ae99a28ba6ae 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -160,7 +160,7 @@ struct vm_area_struct {
 };
 
 struct core_state {
-        int nr_threads;
+        atomic_t nr_threads;
         struct completion startup;
 };
 
diff --git a/kernel/exit.c b/kernel/exit.c
index 988e232254e9..63d82957baae 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);