Get rid of bumping fs_struct refcount in pivot_root(2)

Not because execve races with _that_ are serious - we really
need a situation when final drop of fs_struct refcount is
done by something that used to have it as current->fs.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 17 insertions, 9 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 0a42e0e96027..f7ec283ccfbb 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2131,25 +2131,33 @@ static void chroot_fs_refs(struct path *old_root, struct path *new_root)
 {
         struct task_struct *g, *p;
         struct fs_struct *fs;
+        int count = 0;
 
         read_lock(&tasklist_lock);
         do_each_thread(g, p) {
                 task_lock(p);
                 fs = p->fs;
                 if (fs) {
-                        atomic_inc(&fs->count);
-                        task_unlock(p);
+                        write_lock(&fs->lock);
                         if (fs->root.dentry == old_root->dentry
-                            && fs->root.mnt == old_root->mnt)
-                                set_fs_root(fs, new_root);
+                            && fs->root.mnt == old_root->mnt) {
+                                path_get(new_root);
+                                fs->root = *new_root;
+                                count++;
+                        }
                         if (fs->pwd.dentry == old_root->dentry
-                            && fs->pwd.mnt == old_root->mnt)
-                                set_fs_pwd(fs, new_root);
-                        put_fs_struct(fs);
-                } else
-                        task_unlock(p);
+                            && fs->pwd.mnt == old_root->mnt) {
+                                path_get(new_root);
+                                fs->pwd = *new_root;
+                                count++;
+                        }
+                        write_unlock(&fs->lock);
+                }
+                task_unlock(p);
         } while_each_thread(g, p);
         read_unlock(&tasklist_lock);
+        while (count--)
+                path_put(old_root);
 }
 
 /*