[PATCH] Fix block device inode list corruptions

I've been chasing a weird SELinux bug which shows up mostly when doing
installs of a dev-* rpm (ie. creating and overwriting lots of block
device inodes), but which I've also seen when doing mkinitrd.

It turned out not to be an SELinux problem at all, but a core VFS
S_ISBLK bug.  It seems that SELinux simply widens the race window.

The code at fault is fs/fs-writeback.c:__mark_inode_dirty():

		/*
		 * Only add valid (hashed) inodes to the superblock's
		 * dirty list.  Add blockdev inodes as well.
		 */
		if (!S_ISBLK(inode->i_mode)) {
			if (hlist_unhashed(&inode->i_hash))
				goto out;
			if (inode->i_state & (I_FREEING|I_CLEAR))
				goto out;
		}

The "I_FREEING|I_CLEAR" condition was added after the ISBLK/unhashed
tests were already in the source, but I can't see any reason why we'd
want the I_FREEING test not to apply to block devices.  And indeed, this
results in all sorts of inode list corruptions.  Simply moving the
I_FREEING|I_CLEAR test out of the protection of the S_ISBLK() condition
fixes things entirely.

The existing 2.6 kernel will reliably fail on me in about 2 seconds once
"rpm -Uvh --force dev*.rpm" starts its actual installation of the new
inodes.  With the patch below I can't reproduce it at all.

fs/fs-writeback.c

@@ -90,9 +90,9 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 		if (!S_ISBLK(inode->i_mode)) {
 			if (hlist_unhashed(&inode->i_hash))
 				goto out;
+		}
 		if (inode->i_state & (I_FREEING|I_CLEAR))
 			goto out;
-		}
 
 		/*
 		 * If the inode was already on s_dirty or s_io, don't