Btrfs: add migrate page for metadata inode

Migrate page will directly call the btrfs btree writepage function,
which isn't actually allowed.

Our writepage assumes that you have locked the extent_buffer and
flagged the block as written.  Without doing these steps, we can
corrupt metadata blocks.

A later commit will remove the btree writepage function since
it is really only safely used internally by btrfs.  We
use writepages for everything else.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 25 insertions, 2 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b40dfe48017b..a67b98d58c2a 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -28,6 +28,7 @@
 #include <linux/freezer.h>
 #include <linux/crc32c.h>
 #include <linux/slab.h>
+#include <linux/migrate.h>
 #include "compat.h"
 #include "ctree.h"
 #include "disk-io.h"
@@ -355,6 +356,8 @@ static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
         ret = btree_read_extent_buffer_pages(root, eb, start + PAGE_CACHE_SIZE,
                                              btrfs_header_generation(eb));
         BUG_ON(ret);
+        WARN_ON(!btrfs_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN));
+
         found_start = btrfs_header_bytenr(eb);
         if (found_start != start) {
                 WARN_ON(1);
@@ -693,6 +696,26 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
                                    __btree_submit_bio_done);
 }
 
+static int btree_migratepage(struct address_space *mapping,
+                        struct page *newpage, struct page *page)
+{
+        /*
+         * we can't safely write a btree page from here,
+         * we haven't done the locking hook
+         */
+        if (PageDirty(page))
+                return -EAGAIN;
+        /*
+         * Buffers may be managed in a filesystem specific way.
+         * We must have no buffers or drop them.
+         */
+        if (page_has_private(page) &&
+            !try_to_release_page(page, GFP_KERNEL))
+                return -EAGAIN;
+
+        return migrate_page(mapping, newpage, page);
+}
+
 static int btree_writepage(struct page *page, struct writeback_control *wbc)
 {
         struct extent_io_tree *tree;
@@ -707,8 +730,7 @@ static int btree_writepage(struct page *page, struct writeback_control *wbc)
         }
 
         redirty_page_for_writepage(wbc, page);
-        eb = btrfs_find_tree_block(root, page_offset(page),
-                                      PAGE_CACHE_SIZE);
+        eb = btrfs_find_tree_block(root, page_offset(page), PAGE_CACHE_SIZE);
         WARN_ON(!eb);
 
         was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);
@@ -799,6 +821,7 @@ static const struct address_space_operations btree_aops = {
         .releasepage    = btree_releasepage,
         .invalidatepage = btree_invalidatepage,
         .sync_page      = block_sync_page,
+        .migratepage    = btree_migratepage,
 };
 
 int readahead_tree_block(struct btrfs_root *root, u64 bytenr, u32 blocksize,