From: Al Viro <viro@zeniv.linux.org.uk>
Date: Wed, 27 Mar 2013 00:30:17 +0000 (-0400)
Subject: vt: synchronize_rcu() under spinlock is not nice...
X-Git-Tag: v3.8.6~93
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=240e18740d9f9f45fc31b6a5b792eefc25561c27;p=users%2Fjedix%2Flinux-maple.git

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

commit e8cd81693bbbb15db57d3c9aa7dd90eda4842874 upstream.

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.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index fa7268a93c06..6abb92c22c23 100644
--- 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;
 }