[ 3.5.y.z extended stable ] Patch "vt: synchronize_rcu() under spinlock is not nice..." has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From ed61d0b74ecdb49ceb01f869541432c2e730e5e2 Mon Sep 17 00:00:00 2001
From: Al Viro <viro at zeniv.linux.org.uk>
Date: Tue, 26 Mar 2013 20:30:17 -0400
Subject: [PATCH] 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 at zeniv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/tty/vt/vc_screen.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index fa7268a..6abb92c 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;
 }
--
1.8.1.2