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Fix race in btrfs_mark_extent_written

PATCH New Yan Zheng 1 participant 1 message Nov 12, 2008 Btrfs file system

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Yan Zheng

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PATCH 1/1 Fix race in btrfs_mark_extent_written

Hello,

When extent needs to be split, btrfs_mark_extent_written truncates the extent at first, then inserts a new extent and increases the reference count. The race happens if someone else deletes the old extent before the new extent is inserted. The fix here is increase the reference count in advance. This race is similar to the race in btrfs_drop_extents that fixed a few days ago. Thank you,

Signed-off-by Yan Zheng <[email protected]>

---

fs/btrfs/file.c +14 -4
diff -urp 1/fs/btrfs/file.c 4/fs/btrfs/file.c
@@ -746,6 +746,7 @@ int btrfs_mark_extent_written(struct btr
 	u64 other_end;
 	u64 split = start;
 	u64 locked_end = end;
+	u64 orig_parent;
 	int extent_type;
 	int split_end = 1;
 	int ret;

@@ -890,6 +891,12 @@ again:
 	}
 
 	btrfs_mark_buffer_dirty(leaf);
+
+	orig_parent = leaf->start;
+	ret = btrfs_inc_extent_ref(trans, root, bytenr, num_bytes,
+				   orig_parent, root->root_key.objectid,
+				   trans->transid, inode->i_ino);
+	BUG_ON(ret);
 	btrfs_release_path(root, path);
 
 	key.offset = start;

@@ -910,10 +917,13 @@ again:
 	btrfs_set_file_extent_encryption(leaf, fi, 0);
 	btrfs_set_file_extent_other_encoding(leaf, fi, 0);
 
-	ret = btrfs_inc_extent_ref(trans, root, bytenr, num_bytes,
-				   leaf->start, root->root_key.objectid,
-				   trans->transid, inode->i_ino);
-	BUG_ON(ret);
+	if (orig_parent != leaf->start) {
+		ret = btrfs_update_extent_ref(trans, root, bytenr,
+					      orig_parent, leaf->start,
+					      root->root_key.objectid,
+					      trans->transid, inode->i_ino);
+		BUG_ON(ret);
+	}
 done:
 	btrfs_mark_buffer_dirty(leaf);
 	btrfs_release_path(root, path);