[PATCH 7/8] ext4: don't zeroout if we have inflight unwritten IOs in buffered iomap path

[Ojaswin Mujoo]

The i_conv_pending_ios counter tracks the number of unwritten IOs that
are currently undergoing endio conversion, and is used to prevent
ext4_can_zeroout() from zeroing out unwritten extents that have valid
data pending conversion.

Enable the tracking for the buffered iomap writeback path by incrementing
i_conv_pending_ios once per submitted unwritten ioend in
ext4_iomap_writeback_submit() and decrement it after extent conversion.

Fixes: 8c4f6e337634 ("ext4: introduce a mount option for iomap buffered I/O path")
Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
---
 fs/ext4/inode.c   |  3 +++
 fs/ext4/page-io.c | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 9d7d4da0071f..0c924ad8210b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4585,6 +4585,9 @@ static int ext4_iomap_writeback_submit(struct iomap_writepage_ctx *wpc,
 	if (ioend->io_bio.bi_end_io)
 		bio_clear_flag(&ioend->io_bio, BIO_COMPLETE_IN_TASK);
 
+	if (ioend->io_flags & IOMAP_IOEND_UNWRITTEN)
+		ext4_conv_pending_inc(inode);
+
 	return iomap_ioend_writeback_submit(wpc, error);
 }
 
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 00abef904702..e99816017a18 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -652,6 +652,21 @@ static void ext4_iomap_finish_ioend(struct iomap_ioend *ioend)
 	int credits;
 	int ret, err;
 
+	/*
+	 * We increment conv_pending for each IO we submit but endio might have
+	 * merged them into a single ioend. The data of all merged sub-ioends is
+	 * covered by a single conversion, so drop their counts keeping just
+	 * the one count for the single ioend we will try to convert.
+	 */
+	if (ioend->io_flags & IOMAP_IOEND_UNWRITTEN) {
+		struct iomap_ioend *sub;
+
+		list_for_each_entry(sub, &ioend->io_list, io_list) {
+			if (sub->io_flags & IOMAP_IOEND_UNWRITTEN)
+				ext4_conv_pending_dec(inode);
+		}
+	}
+
 	ret = blk_status_to_errno(ioend->io_bio.bi_status);
 	if (is_disksize_grow)
 		trace_ext4_iomap_wb_disksize_pending_complete(ioend->io_inode,
@@ -704,6 +719,10 @@ static void ext4_iomap_finish_ioend(struct iomap_ioend *ioend)
 			 inode->i_ino, ret);
 	}
 out:
+	/* Drop the count of the head ioend now that conversion is done. */
+	if (ioend->io_flags & IOMAP_IOEND_UNWRITTEN)
+		ext4_conv_pending_dec(inode);
+
 	iomap_finish_ioends(ioend, ret);
 }
 

-- 
2.55.0