[PATCH] 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.

[akpm: too late for 2.6.17 - suitable for 2.6.17.x after it has settled]

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index a5cc4c8..29af584 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -852,6 +852,9 @@ 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)
@@ -918,6 +921,8 @@ static struct mapped_device *alloc_dev(unsigned int minor, int persistent)
        blk_cleanup_queue(md->queue);
        free_minor(minor);
  bad1:
+       module_put(THIS_MODULE);
+ bad0:
        kfree(md);
        return NULL;
 }
@@ -941,6 +946,7 @@ static void free_dev(struct mapped_device *md)
 
        put_disk(md->disk);
        blk_cleanup_queue(md->queue);
+       module_put(THIS_MODULE);
        kfree(md);
 }