device-dax: fix cdev leak

BugLink: http://bugs.launchpad.net/bugs/1692898
commit ed01e50acdd3e4a640cf9ebd28a7e810c3ceca97 upstream.

If device_add() fails, cleanup the cdev. Otherwise, we leak a kobj_map()
with a stale device number.

As Jason points out, there is a small possibility that userspace has
opened and mapped the device in the time between cdev_add() and the
device_add() failure. We need a new kill_dax_dev() helper to invalidate
any established mappings.

Fixes: ba09c01d2fa8 ("dax: convert to the cdev api")
Reported-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index 53a016c3dffa4093e168e1c3a4e0db14cb1a07d5..b88b2a2f70f49975d082fcef8637c0d3af14a8db 100644 (file)
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -646,13 +646,10 @@ static void dax_dev_release(struct device *dev)
        kfree(dax_dev);
 }
 
-static void unregister_dax_dev(void *dev)
+static void kill_dax_dev(struct dax_dev *dax_dev)
 {
-       struct dax_dev *dax_dev = to_dax_dev(dev);
        struct cdev *cdev = &dax_dev->cdev;
 
-       dev_dbg(dev, "%s\n", __func__);
-
        /*
         * Note, rcu is not protecting the liveness of dax_dev, rcu is
         * ensuring that any fault handlers that might have seen
@@ -664,6 +661,15 @@ static void unregister_dax_dev(void *dev)
        synchronize_srcu(&dax_srcu);
        unmap_mapping_range(dax_dev->inode->i_mapping, 0, 0, 1);
        cdev_del(cdev);
+}
+
+static void unregister_dax_dev(void *dev)
+{
+       struct dax_dev *dax_dev = to_dax_dev(dev);
+
+       dev_dbg(dev, "%s\n", __func__);
+
+       kill_dax_dev(dax_dev);
        device_unregister(dev);
 }
 
@@ -740,6 +746,7 @@ struct dax_dev *devm_create_dax_dev(struct dax_region *dax_region,
        dev_set_name(dev, "dax%d.%d", dax_region->id, dax_dev->id);
        rc = device_add(dev);
        if (rc) {
+               kill_dax_dev(dax_dev);
                put_device(dev);
                return ERR_PTR(rc);
        }