btrfs: extent_io: Handle errors better in extent_write_full_page()

Since now flush_write_bio() could return error, kill the BUG_ON() first.
Then don't call flush_write_bio() unconditionally, instead we check the
return value from __extent_writepage() first.

If __extent_writepage() fails, we do cleanup, and return error without
submitting the possible corrupted or half-baked bio.

If __extent_writepage() successes, then we call flush_write_bio() and
return the result.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -170,6 +170,16 @@ static int __must_check submit_one_bio(struct bio *bio, int mirror_num,
 	return blk_status_to_errno(ret);
 }
 
+/* Cleanup unsubmitted bios */
+static void end_write_bio(struct extent_page_data *epd, int ret)
+{
+	if (epd->bio) {
+		epd->bio->bi_status = errno_to_blk_status(ret);
+		bio_endio(epd->bio);
+		epd->bio = NULL;
+	}
+}
+
 /*
  * Submit bio from extent page data via submit_one_bio
  *
@@ -3397,6 +3407,9 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
  * records are inserted to lock ranges in the tree, and as dirty areas
  * are found, they are marked writeback.  Then the lock bits are removed
  * and the end_io handler clears the writeback ranges
+ *
+ * Return 0 if everything goes well.
+ * Return <0 for error.
  */
 static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 			      struct extent_page_data *epd)
@@ -3466,6 +3479,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
 		end_extent_writepage(page, ret, start, page_end);
 	}
 	unlock_page(page);
+	ASSERT(ret <= 0);
 	return ret;
 
 done_unlocked:
@@ -4007,7 +4021,6 @@ static int extent_write_cache_pages(struct address_space *mapping,
 int extent_write_full_page(struct page *page, struct writeback_control *wbc)
 {
 	int ret;
-	int flush_ret;
 	struct extent_page_data epd = {
 		.bio = NULL,
 		.tree = &BTRFS_I(page->mapping->host)->io_tree,
@@ -4016,9 +4029,14 @@ int extent_write_full_page(struct page *page, struct writeback_control *wbc)
 	};
 
 	ret = __extent_writepage(page, wbc, &epd);
+	ASSERT(ret <= 0);
+	if (ret < 0) {
+		end_write_bio(&epd, ret);
+		return ret;
+	}
 
-	flush_ret = flush_write_bio(&epd);
-	BUG_ON(flush_ret < 0);
+	ret = flush_write_bio(&epd);
+	ASSERT(ret <= 0);
 	return ret;
 }