btrfs: make __extent_writepage_io() to write specified range only

Function __extent_writepage_io() is designed to find all dirty ranges of
a page, and add the dirty ranges to the bio_ctrl for submission.
It requires all the dirtied ranges to be covered by an ordered extent.

It gets called in two locations, but one call site is not subpage aware:

- __extent_writepage()
  It gets called when writepage_delalloc() returned 0, which means
  writepage_delalloc() has handled delalloc for all subpage sectors
  inside the page.

  So this call site is OK.

- extent_write_locked_range()
  This call site is utilized by zoned support, and in this case, we may
  only run delalloc range for a subset of the page, like this: (64K page
  size)

  0     16K     32K     48K     64K
  |/////|       |///////|       |

  In the above case, if extent_write_locked_range() is only triggered for
  range [0, 16K), __extent_writepage_io() would still try to submit
  the dirty range of [32K, 48K), then it would not find any ordered
  extent for it and triggers various ASSERT()s.

Fix this problem by:

- Introducing @start and @len parameters to specify the range

  For the first call site, we just pass the whole page, and the behavior
  is not touched, since run_delalloc_range() for the page should have
  created all ordered extents for the page.

  For the second call site, we avoid touching anything beyond the
  range, thus avoiding the dirty range which is not yet covered by any
  delalloc range.

- Making btrfs_folio_assert_not_dirty() subpage aware
  The only caller is inside __extent_writepage_io(), and since that
  caller now accepts a subpage range, we should also check the subpage
  range other than the whole page.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -1339,20 +1339,23 @@ static void find_next_dirty_byte(struct btrfs_fs_info *fs_info,
  * < 0 if there were errors (page still locked)
  */
 static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
-				 struct page *page,
+				 struct page *page, u64 start, u32 len,
 				 struct btrfs_bio_ctrl *bio_ctrl,
 				 loff_t i_size,
 				 int *nr_ret)
 {
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
-	u64 cur = page_offset(page);
-	u64 end = cur + PAGE_SIZE - 1;
+	u64 cur = start;
+	u64 end = start + len - 1;
 	u64 extent_offset;
 	u64 block_start;
 	struct extent_map *em;
 	int ret = 0;
 	int nr = 0;
 
+	ASSERT(start >= page_offset(page) &&
+	       start + len <= page_offset(page) + PAGE_SIZE);
+
 	ret = btrfs_writepage_cow_fixup(page);
 	if (ret) {
 		/* Fixup worker will requeue */
@@ -1441,7 +1444,7 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
 		nr++;
 	}
 
-	btrfs_folio_assert_not_dirty(fs_info, page_folio(page));
+	btrfs_folio_assert_not_dirty(fs_info, page_folio(page), start, len);
 	*nr_ret = nr;
 	return 0;
 
@@ -1499,7 +1502,8 @@ static int __extent_writepage(struct page *page, struct btrfs_bio_ctrl *bio_ctrl
 	if (ret)
 		goto done;
 
-	ret = __extent_writepage_io(BTRFS_I(inode), page, bio_ctrl, i_size, &nr);
+	ret = __extent_writepage_io(BTRFS_I(inode), page, page_offset(page),
+				    PAGE_SIZE, bio_ctrl, i_size, &nr);
 	if (ret == 1)
 		return 0;
 
@@ -2251,8 +2255,8 @@ void extent_write_locked_range(struct inode *inode, struct page *locked_page,
 			clear_page_dirty_for_io(page);
 		}
 
-		ret = __extent_writepage_io(BTRFS_I(inode), page, &bio_ctrl,
-					    i_size, &nr);
+		ret = __extent_writepage_io(BTRFS_I(inode), page, cur, cur_len,
+					    &bio_ctrl, i_size, &nr);
 		if (ret == 1)
 			goto next_page;
 

fs/btrfs/subpage.c

@@ -703,19 +703,29 @@ IMPLEMENT_BTRFS_PAGE_OPS(checked, folio_set_checked, folio_clear_checked,
  * Make sure not only the page dirty bit is cleared, but also subpage dirty bit
  * is cleared.
  */
-void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info, struct folio *folio)
+void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info,
+				  struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_subpage *subpage;
+	unsigned int start_bit;
+	unsigned int nbits;
+	unsigned long flags;
 
 	if (!IS_ENABLED(CONFIG_BTRFS_ASSERT))
 		return;
 
-	ASSERT(!folio_test_dirty(folio));
-	if (!btrfs_is_subpage(fs_info, folio->mapping))
+	if (!btrfs_is_subpage(fs_info, folio->mapping)) {
+		ASSERT(!folio_test_dirty(folio));
 		return;
+	}
 
-	ASSERT(folio_test_private(folio) && folio_get_private(folio));
-	ASSERT(subpage_test_bitmap_all_zero(fs_info, subpage, dirty));
+	start_bit = subpage_calc_start_bit(fs_info, folio, dirty, start, len);
+	nbits = len >> fs_info->sectorsize_bits;
+	subpage = folio_get_private(folio);
+	ASSERT(subpage);
+	spin_lock_irqsave(&subpage->lock, flags);
+	ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
+	spin_unlock_irqrestore(&subpage->lock, flags);
 }
 
 /*

fs/btrfs/subpage.h

@@ -156,7 +156,8 @@ DECLARE_BTRFS_SUBPAGE_OPS(checked);
 bool btrfs_subpage_clear_and_test_dirty(const struct btrfs_fs_info *fs_info,
 					struct folio *folio, u64 start, u32 len);
 
-void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info, struct folio *folio);
+void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info,
+				  struct folio *folio, u64 start, u32 len);
 void btrfs_folio_unlock_writer(struct btrfs_fs_info *fs_info,
 			       struct folio *folio, u64 start, u32 len);
 void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,