xfs: fallback to vmalloc for large buffers in xfs_attrmulti_attr_get

xfsdump uses for a large buffer for extended attributes, which has a
kmalloc'd shadow buffer in the kernel. This can fail after the
system has been running for some time as it is a high order
allocation. Add a fallback to vmalloc so that it doesn't require
contiguous memory and so won't randomly fail while xfsdump is
running.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_ioctl.c

@@ -450,9 +450,12 @@ xfs_attrmulti_attr_get(
 
 	if (*len > XATTR_SIZE_MAX)
 		return EINVAL;
-	kbuf = kmalloc(*len, GFP_KERNEL);
-	if (!kbuf)
-		return ENOMEM;
+	kbuf = kmem_zalloc(*len, KM_SLEEP | KM_MAYFAIL);
+	if (!kbuf) {
+		kbuf = kmem_zalloc_large(*len);
+		if (!kbuf)
+			return ENOMEM;
+	}
 
 	error = xfs_attr_get(XFS_I(inode), name, kbuf, (int *)len, flags);
 	if (error)
@@ -462,7 +465,10 @@ xfs_attrmulti_attr_get(
 		error = EFAULT;
 
  out_kfree:
-	kfree(kbuf);
+	if (is_vmalloc_addr(kbuf))
+		kmem_free_large(kbuf);
+	else
+		kmem_free(kbuf);
 	return error;
 }