dm: add module ref counting

The reference counting on dm-mod is zero if no mapped devices are open.  This
is incorrect, and can lead to an oops if the module is unloaded while mapped
devices exist.

This patch claims a reference to the module whenever a device is created, and
drops it again when the device is freed.

Devices must be removed before dm-mod is unloaded.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index f6c8e8e4e8e2011a8ba003578df48e0f3d79bdfe..973b6f6ff3526bb4cd69ad31887e65641dca5031 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -788,6 +788,9 @@ static struct mapped_device *alloc_dev(unsigned int minor, int persistent)
                return NULL;
        }
 
+       if (!try_module_get(THIS_MODULE))
+               goto bad0;
+
        /* get a minor number for the dev */
        r = persistent ? specific_minor(md, minor) : next_free_minor(md, &minor);
        if (r < 0)
@@ -848,6 +851,8 @@ static struct mapped_device *alloc_dev(unsigned int minor, int persistent)
        blk_put_queue(md->queue);
        free_minor(minor);
  bad1:
+       module_put(THIS_MODULE);
+ bad0:
        kfree(md);
        return NULL;
 }
@@ -866,6 +871,7 @@ static void free_dev(struct mapped_device *md)
        free_minor(minor);
        put_disk(md->disk);
        blk_put_queue(md->queue);
+       module_put(THIS_MODULE);
        kfree(md);
 }