v4.19.13 snapshot.
diff --git a/fs/stack.c b/fs/stack.c
new file mode 100644
index 0000000..a54e33e
--- /dev/null
+++ b/fs/stack.c
@@ -0,0 +1,76 @@
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/fs_stack.h>
+
+/* does _NOT_ require i_mutex to be held.
+ *
+ * This function cannot be inlined since i_size_{read,write} is rather
+ * heavy-weight on 32-bit systems
+ */
+void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
+{
+ loff_t i_size;
+ blkcnt_t i_blocks;
+
+ /*
+ * i_size_read() includes its own seqlocking and protection from
+ * preemption (see include/linux/fs.h): we need nothing extra for
+ * that here, and prefer to avoid nesting locks than attempt to keep
+ * i_size and i_blocks in sync together.
+ */
+ i_size = i_size_read(src);
+
+ /*
+ * But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to
+ * keep the two halves of i_blocks in sync despite SMP or PREEMPT -
+ * though stat's generic_fillattr() doesn't bother, and we won't be
+ * applying quotas (where i_blocks does become important) at the
+ * upper level.
+ *
+ * We don't actually know what locking is used at the lower level;
+ * but if it's a filesystem that supports quotas, it will be using
+ * i_lock as in inode_add_bytes().
+ */
+ if (sizeof(i_blocks) > sizeof(long))
+ spin_lock(&src->i_lock);
+ i_blocks = src->i_blocks;
+ if (sizeof(i_blocks) > sizeof(long))
+ spin_unlock(&src->i_lock);
+
+ /*
+ * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
+ * fsstack_copy_inode_size() to hold some lock around
+ * i_size_write(), otherwise i_size_read() may spin forever (see
+ * include/linux/fs.h). We don't necessarily hold i_mutex when this
+ * is called, so take i_lock for that case.
+ *
+ * And if CONFIG_LBDAF (on 32-bit), continue our effort to keep the
+ * two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
+ * for that case too, and do both at once by combining the tests.
+ *
+ * There is none of this locking overhead in the 64-bit case.
+ */
+ if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
+ spin_lock(&dst->i_lock);
+ i_size_write(dst, i_size);
+ dst->i_blocks = i_blocks;
+ if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
+ spin_unlock(&dst->i_lock);
+}
+EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
+
+/* copy all attributes */
+void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
+{
+ dest->i_mode = src->i_mode;
+ dest->i_uid = src->i_uid;
+ dest->i_gid = src->i_gid;
+ dest->i_rdev = src->i_rdev;
+ dest->i_atime = src->i_atime;
+ dest->i_mtime = src->i_mtime;
+ dest->i_ctime = src->i_ctime;
+ dest->i_blkbits = src->i_blkbits;
+ dest->i_flags = src->i_flags;
+ set_nlink(dest, src->i_nlink);
+}
+EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);