btrfs: only call __extent_writepage_io from extent_write_locked_range

__extent_writepage does a lot of things that make no sense for
extent_write_locked_range, given that extent_write_locked_range itself is
called from __extent_writepage either directly or through a workqueue,
and all this work has already been done in the first invocation and the
pages haven't been unlocked since.  Call __extent_writepage_io directly
instead and open code the logic tracked in
btrfs_bio_ctrl::extent_locked.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -103,12 +103,6 @@ struct btrfs_bio_ctrl {
 	blk_opf_t opf;
 	btrfs_bio_end_io_t end_io_func;
 	struct writeback_control *wbc;
-
-	/*
-	 * Tell writepage not to lock the state bits for this range, it still
-	 * does the unlocking.
-	 */
-	bool extent_locked;
 };
 
 static void submit_one_bio(struct btrfs_bio_ctrl *bio_ctrl)
@@ -1475,7 +1469,6 @@ static int __extent_writepage(struct page *page, struct btrfs_bio_ctrl *bio_ctrl
 {
 	struct folio *folio = page_folio(page);
 	struct inode *inode = page->mapping->host;
-	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	const u64 page_start = page_offset(page);
 	const u64 page_end = page_start + PAGE_SIZE - 1;
 	int ret;
@@ -1503,13 +1496,11 @@ static int __extent_writepage(struct page *page, struct btrfs_bio_ctrl *bio_ctrl
 	if (ret < 0)
 		goto done;
 
-	if (!bio_ctrl->extent_locked) {
 	ret = writepage_delalloc(BTRFS_I(inode), page, bio_ctrl->wbc);
 	if (ret == 1)
 		return 0;
 	if (ret)
 		goto done;
-	}
 
 	ret = __extent_writepage_io(BTRFS_I(inode), page, bio_ctrl, i_size, &nr);
 	if (ret == 1)
@@ -1525,21 +1516,7 @@ static int __extent_writepage(struct page *page, struct btrfs_bio_ctrl *bio_ctrl
 	}
 	if (ret)
 		end_extent_writepage(page, ret, page_start, page_end);
-	if (bio_ctrl->extent_locked) {
-		struct writeback_control *wbc = bio_ctrl->wbc;
-
-		/*
-		 * If bio_ctrl->extent_locked, it's from extent_write_locked_range(),
-		 * the page can either be locked by lock_page() or
-		 * process_one_page().
-		 * Let btrfs_page_unlock_writer() handle both cases.
-		 */
-		ASSERT(wbc);
-		btrfs_page_unlock_writer(fs_info, page, wbc->range_start,
-					 wbc->range_end + 1 - wbc->range_start);
-	} else {
 	unlock_page(page);
-	}
 	ASSERT(ret <= 0);
 	return ret;
 }
@@ -2239,10 +2216,10 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
 	int first_error = 0;
 	int ret = 0;
 	struct address_space *mapping = inode->i_mapping;
-	struct page *page;
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+	const u32 sectorsize = fs_info->sectorsize;
+	loff_t i_size = i_size_read(inode);
 	u64 cur = start;
-	unsigned long nr_pages;
-	const u32 sectorsize = btrfs_sb(inode->i_sb)->sectorsize;
 	struct writeback_control wbc_writepages = {
 		.sync_mode	= WB_SYNC_ALL,
 		.range_start	= start,
@@ -2254,17 +2231,15 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
 		/* We're called from an async helper function */
 		.opf = REQ_OP_WRITE | REQ_BTRFS_CGROUP_PUNT |
 			wbc_to_write_flags(&wbc_writepages),
-		.extent_locked = 1,
 	};
 
 	ASSERT(IS_ALIGNED(start, sectorsize) && IS_ALIGNED(end + 1, sectorsize));
-	nr_pages = (round_up(end, PAGE_SIZE) - round_down(start, PAGE_SIZE)) >>
-		   PAGE_SHIFT;
-	wbc_writepages.nr_to_write = nr_pages * 2;
 
 	wbc_attach_fdatawrite_inode(&wbc_writepages, inode);
 	while (cur <= end) {
 		u64 cur_end = min(round_down(cur, PAGE_SIZE) + PAGE_SIZE - 1, end);
+		struct page *page;
+		int nr = 0;
 
 		page = find_get_page(mapping, cur >> PAGE_SHIFT);
 		/*
@@ -2275,12 +2250,25 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
 		ASSERT(PageLocked(page));
 		ASSERT(PageDirty(page));
 		clear_page_dirty_for_io(page);
-		ret = __extent_writepage(page, &bio_ctrl);
-		ASSERT(ret <= 0);
+
+		ret = __extent_writepage_io(BTRFS_I(inode), page, &bio_ctrl,
+					    i_size, &nr);
+		if (ret == 1)
+			goto next_page;
+
+		/* Make sure the mapping tag for page dirty gets cleared. */
+		if (nr == 0) {
+			set_page_writeback(page);
+			end_page_writeback(page);
+		}
+		if (ret)
+			end_extent_writepage(page, ret, cur, cur_end);
+		btrfs_page_unlock_writer(fs_info, page, cur, cur_end + 1 - cur);
 		if (ret < 0) {
 			found_error = true;
 			first_error = ret;
 		}
+next_page:
 		put_page(page);
 		cur = cur_end + 1;
 	}
@@ -2301,7 +2289,6 @@ int extent_writepages(struct address_space *mapping,
 	struct btrfs_bio_ctrl bio_ctrl = {
 		.wbc = wbc,
 		.opf = REQ_OP_WRITE | wbc_to_write_flags(wbc),
-		.extent_locked = 0,
 	};
 
 	/*