vt: synchronize_rcu() under spinlock is not nice...

vcs_poll_data_free() calls unregister_vt_notifier(), which calls
atomic_notifier_chain_unregister(), which calls synchronize_rcu().
Do it *after* we'd dropped ->f_lock.

Cc: stable@vger.kernel.org (all kernels since 2.6.37)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index e4ca345873c3279761f8dcf6cee3f06053205088..d7799deacb21a66805d8e4308bcc199b64894fbf 100644 (file)
--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -93,7 +93,7 @@ vcs_poll_data_free(struct vcs_poll_data *poll)
 static struct vcs_poll_data *
 vcs_poll_data_get(struct file *file)
 {
-       struct vcs_poll_data *poll = file->private_data;
+       struct vcs_poll_data *poll = file->private_data, *kill = NULL;
 
        if (poll)
                return poll;
@@ -122,10 +122,12 @@ vcs_poll_data_get(struct file *file)
                file->private_data = poll;
        } else {
                /* someone else raced ahead of us */
-               vcs_poll_data_free(poll);
+               kill = poll;
                poll = file->private_data;
        }
        spin_unlock(&file->f_lock);
+       if (kill)
+               vcs_poll_data_free(kill);
 
        return poll;
 }