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[dm-devel] [PATCH] dm free minor after unlink gendisk



Hello,

free_dev() releases minor number before unregistering gendisk.
It creates a window where two registered gendisk with same number
exist, which will cause problem.

Typically, if you run the following script,
you will hit WARN_ON() in kref_get().

#!/bin/sh
(while dmsetup create a --notable; do dmsetup remove a; done) &
(while dmsetup create b --notable; do dmsetup remove b; done) &

Attached patch fixes this problem.

-- 
Jun'ichi Nomura, NEC Solutions (America), Inc.
minor number should be freed after del_gendisk().
Otherwise, there could be a window where 2 registered gendisk
has same minor number.

Signed-off-by: Jun'ichi Nomura <j-nomura ce jp nec com>

--- linux-2.6.15.orig/drivers/md/dm.c	2006-02-24 11:05:05.000000000 -0500
+++ linux-2.6.15/drivers/md/dm.c	2006-02-24 11:17:54.000000000 -0500
@@ -812,14 +812,16 @@ static struct mapped_device *alloc_dev(u
 
 static void free_dev(struct mapped_device *md)
 {
+	unsigned int minor = md->disk->first_minor;
+
 	if (md->suspended_bdev) {
 		thaw_bdev(md->suspended_bdev, NULL);
 		bdput(md->suspended_bdev);
 	}
-	free_minor(md->disk->first_minor);
 	mempool_destroy(md->tio_pool);
 	mempool_destroy(md->io_pool);
 	del_gendisk(md->disk);
+	free_minor(minor);
 	put_disk(md->disk);
 	blk_put_queue(md->queue);
 	kfree(md);

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