ext4: move keep_towrite handling to ext4_bio_write_page()

When we are writing back page but we cannot for some reason write all
its buffers (e.g. because we cannot allocate blocks in current context) we
have to keep TOWRITE tag set in the mapping as otherwise racing
WB_SYNC_ALL writeback that could write these buffers can skip the page
and result in data loss.  We will need this logic for writeback during
transaction commit so move the logic from ext4_writepage() to
ext4_bio_write_page().

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20221207112722.22220-2-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -3757,8 +3757,7 @@ extern void ext4_end_io_rsv_work(struct work_struct *work);
 extern void ext4_io_submit(struct ext4_io_submit *io);
 extern int ext4_bio_write_page(struct ext4_io_submit *io,
 			       struct page *page,
-			       int len,
+			       int len);
-			       bool keep_towrite);
 extern struct ext4_io_end_vec *ext4_alloc_io_end_vec(ext4_io_end_t *io_end);
 extern struct ext4_io_end_vec *ext4_last_io_end_vec(ext4_io_end_t *io_end);
 

fs/ext4/inode.c

@@ -2016,7 +2016,6 @@ static int ext4_writepage(struct page *page,
 	struct buffer_head *page_bufs = NULL;
 	struct inode *inode = page->mapping->host;
 	struct ext4_io_submit io_submit;
-	bool keep_towrite = false;
 
 	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) {
 		folio_invalidate(folio, 0, folio_size(folio));
@@ -2074,7 +2073,6 @@ static int ext4_writepage(struct page *page,
 			unlock_page(page);
 			return 0;
 		}
-		keep_towrite = true;
 	}
 
 	if (PageChecked(page) && ext4_should_journal_data(inode))
@@ -2091,7 +2089,7 @@ static int ext4_writepage(struct page *page,
 		unlock_page(page);
 		return -ENOMEM;
 	}
-	ret = ext4_bio_write_page(&io_submit, page, len, keep_towrite);
+	ret = ext4_bio_write_page(&io_submit, page, len);
 	ext4_io_submit(&io_submit);
 	/* Drop io_end reference we got from init */
 	ext4_put_io_end_defer(io_submit.io_end);
@@ -2125,7 +2123,7 @@ static int mpage_submit_page(struct mpage_da_data *mpd, struct page *page)
 		len = size & ~PAGE_MASK;
 	else
 		len = PAGE_SIZE;
-	err = ext4_bio_write_page(&mpd->io_submit, page, len, false);
+	err = ext4_bio_write_page(&mpd->io_submit, page, len);
 	if (!err)
 		mpd->wbc->nr_to_write--;
 	mpd->first_page++;

fs/ext4/page-io.c

@@ -430,8 +430,7 @@ submit_and_retry:
 
 int ext4_bio_write_page(struct ext4_io_submit *io,
 			struct page *page,
-			int len,
+			int len)
-			bool keep_towrite)
 {
 	struct page *bounce_page = NULL;
 	struct inode *inode = page->mapping->host;
@@ -441,14 +440,11 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 	int nr_submitted = 0;
 	int nr_to_submit = 0;
 	struct writeback_control *wbc = io->io_wbc;
+	bool keep_towrite = false;
 
 	BUG_ON(!PageLocked(page));
 	BUG_ON(PageWriteback(page));
 
-	if (keep_towrite)
-		set_page_writeback_keepwrite(page);
-	else
-		set_page_writeback(page);
 	ClearPageError(page);
 
 	/*
@@ -483,12 +479,17 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 			if (!buffer_mapped(bh))
 				clear_buffer_dirty(bh);
 			/*
-			 * Keeping dirty some buffer we cannot write? Make
+			 * Keeping dirty some buffer we cannot write? Make sure
-			 * sure to redirty the page. This happens e.g. when
+			 * to redirty the page and keep TOWRITE tag so that
-			 * doing writeout for transaction commit.
+			 * racing WB_SYNC_ALL writeback does not skip the page.
+			 * This happens e.g. when doing writeout for
+			 * transaction commit.
 			 */
-			if (buffer_dirty(bh) && !PageDirty(page))
+			if (buffer_dirty(bh)) {
-				redirty_page_for_writepage(wbc, page);
+				if (!PageDirty(page))
+					redirty_page_for_writepage(wbc, page);
+				keep_towrite = true;
+			}
 			if (io->io_bio)
 				ext4_io_submit(io);
 			continue;
@@ -500,6 +501,10 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 		nr_to_submit++;
 	} while ((bh = bh->b_this_page) != head);
 
+	/* Nothing to submit? Just unlock the page... */
+	if (!nr_to_submit)
+		goto unlock;
+
 	bh = head = page_buffers(page);
 
 	/*
@@ -550,6 +555,11 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 		}
 	}
 
+	if (keep_towrite)
+		set_page_writeback_keepwrite(page);
+	else
+		set_page_writeback(page);
+
 	/* Now submit buffers to write */
 	do {
 		if (!buffer_async_write(bh))
@@ -558,11 +568,7 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 				 bounce_page ? bounce_page : page, bh);
 		nr_submitted++;
 	} while ((bh = bh->b_this_page) != head);
-
 unlock:
 	unlock_page(page);
-	/* Nothing submitted - we have to end page writeback */
-	if (!nr_submitted)
-		end_page_writeback(page);
 	return ret;
 }