hfs: fix memory leak when unmounting

When an HFS filesystem is unmounted, it leaks a 2-page bitmap.  Also,
under extreme memory pressure, it's possible that hfs_releasepage() may
use a tree pointer that has not been initialized, and if so, the release
request should just be rejected.

[akpm@linux-foundation.org: free_pages(0) is legal, remove obvious comment]
Signed-off-by: Dave Anderson <anderson@redhat.com>
Tested-by: Eugene Teo <eugeneteo@kernel.sg>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hfs/inode.c

@@ -70,6 +70,10 @@ static int hfs_releasepage(struct page *page, gfp_t mask)
 		BUG();
 		return 0;
 	}
+
+	if (!tree)
+		return 0;
+
 	if (tree->node_size >= PAGE_CACHE_SIZE) {
 		nidx = page->index >> (tree->node_size_shift - PAGE_CACHE_SHIFT);
 		spin_lock(&tree->hash_lock);

fs/hfs/mdb.c

@@ -349,6 +349,7 @@ void hfs_mdb_put(struct super_block *sb)
 	if (HFS_SB(sb)->nls_disk)
 		unload_nls(HFS_SB(sb)->nls_disk);
 
+	free_pages((unsigned long)HFS_SB(sb)->bitmap, PAGE_SIZE < 8192 ? 1 : 0);
 	kfree(HFS_SB(sb));
 	sb->s_fs_info = NULL;
 }