[ 13/56] vt: synchronize_rcu() under spinlock is not nice...

Greg Kroah-Hartman
2013-04-02T23:02:26Z

From: Al Viro <viro@zeniv.linux.org.uk>

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>

---
drivers/tty/vt/vc_screen.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -92,7 +92,7 @@ vcs_poll_data_free(struct vcs_poll_data
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;
@@ -121,10 +121,12 @@ 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;
}