mm_for_maps: shift down_read(mmap_sem) to the caller

mm_for_maps() takes ->mmap_sem after security checks, this looks
strange and obfuscates the locking rules. Move this lock to its
single caller, m_start().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 64a72e2e7650..8f5c05d3dbd3 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -189,6 +189,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
                 priv->task = NULL;
                 return NULL;
         }
+        down_read(&mm->mmap_sem);
 
         /* start from the Nth VMA */
         for (p = rb_first(&mm->mm_rb); p; p = rb_next(p))