btrfs: integrating raid-repair and scrub-fixup-nodatasum

This ties nodatasum fixup in scrub together with raid repair patches. While
both series are working fine alone, scrub will report uncorrectable errors
if they occur in a nodatasum extent *and* the page is in the page cache.

Previously, we would have triggered readpage to find good data and do the
repair. However, readpage wouldn't read anything in the case where the page
is up to date in the cache. So, we simply take that good data we have and
call repair_io_failure directly (unless the page in the cache is dirty).
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>

fs/btrfs/scrub.c

@@ -24,6 +24,7 @@
 #include "ordered-data.h"
 #include "transaction.h"
 #include "backref.h"
+#include "extent_io.h"
 
 /*
  * This is only the first step towards a full-features scrub. It reads all
@@ -360,13 +361,13 @@ static void scrub_print_warning(const char *errstr, struct scrub_bio *sbio,
 
 static int scrub_fixup_readpage(u64 inum, u64 offset, u64 root, void *ctx)
 {
-	struct page *page;
+	struct page *page = NULL;
 	unsigned long index;
 	struct scrub_fixup_nodatasum *fixup = ctx;
 	int ret;
-	int corrected;
+	int corrected = 0;
 	struct btrfs_key key;
-	struct inode *inode;
+	struct inode *inode = NULL;
 	u64 end = offset + PAGE_SIZE - 1;
 	struct btrfs_root *local_root;
 
@@ -384,34 +385,75 @@ static int scrub_fixup_readpage(u64 inum, u64 offset, u64 root, void *ctx)
 	if (IS_ERR(inode))
 		return PTR_ERR(inode);
 
-	ret = set_extent_bit(&BTRFS_I(inode)->io_tree, offset, end,
-				EXTENT_DAMAGED, 0, NULL, NULL, GFP_NOFS);
-
-	/* set_extent_bit should either succeed or give proper error */
-	WARN_ON(ret > 0);
-	if (ret)
-		return ret < 0 ? ret : -EFAULT;
-
 	index = offset >> PAGE_CACHE_SHIFT;
 
 	page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);
-	if (!page)
-		return -ENOMEM;
+	if (!page) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (PageUptodate(page)) {
+		struct btrfs_mapping_tree *map_tree;
+		if (PageDirty(page)) {
+			/*
+			 * we need to write the data to the defect sector. the
+			 * data that was in that sector is not in memory,
+			 * because the page was modified. we must not write the
+			 * modified page to that sector.
+			 *
+			 * TODO: what could be done here: wait for the delalloc
+			 *       runner to write out that page (might involve
+			 *       COW) and see whether the sector is still
+			 *       referenced afterwards.
+			 *
+			 * For the meantime, we'll treat this error
+			 * incorrectable, although there is a chance that a
+			 * later scrub will find the bad sector again and that
+			 * there's no dirty page in memory, then.
+			 */
+			ret = -EIO;
+			goto out;
+		}
+		map_tree = &BTRFS_I(inode)->root->fs_info->mapping_tree;
+		ret = repair_io_failure(map_tree, offset, PAGE_SIZE,
+					fixup->logical, page,
+					fixup->mirror_num);
+		unlock_page(page);
+		corrected = !ret;
+	} else {
+		/*
+		 * we need to get good data first. the general readpage path
+		 * will call repair_io_failure for us, we just have to make
+		 * sure we read the bad mirror.
+		 */
+		ret = set_extent_bits(&BTRFS_I(inode)->io_tree, offset, end,
+					EXTENT_DAMAGED, GFP_NOFS);
+		if (ret) {
+			/* set_extent_bits should give proper error */
+			WARN_ON(ret > 0);
+			if (ret > 0)
+				ret = -EFAULT;
+			goto out;
+		}
 
-	ret = extent_read_full_page(&BTRFS_I(inode)->io_tree, page,
-					btrfs_get_extent, fixup->mirror_num);
-	wait_on_page_locked(page);
-	corrected = !test_range_bit(&BTRFS_I(inode)->io_tree, offset, end,
-					EXTENT_DAMAGED, 0, NULL);
+		ret = extent_read_full_page(&BTRFS_I(inode)->io_tree, page,
+						btrfs_get_extent,
+						fixup->mirror_num);
+		wait_on_page_locked(page);
 
-	if (corrected)
-		WARN_ON(!PageUptodate(page));
-	else
-		clear_extent_bit(&BTRFS_I(inode)->io_tree, offset, end,
-					EXTENT_DAMAGED, 0, 0, NULL, GFP_NOFS);
+		corrected = !test_range_bit(&BTRFS_I(inode)->io_tree, offset,
+						end, EXTENT_DAMAGED, 0, NULL);
+		if (!corrected)
+			clear_extent_bits(&BTRFS_I(inode)->io_tree, offset, end,
+						EXTENT_DAMAGED, GFP_NOFS);
+	}
 
-	put_page(page);
-	iput(inode);
+out:
+	if (page)
+		put_page(page);
+	if (inode)
+		iput(inode);
 
 	if (ret < 0)
 		return ret;