[Devel] [PATCH hci-8.1 v9 09/10] dm-qcow2: flag the image for check after a reverted L1/L2 writeback

[Alexander Ivanov]

A failed L1/L2 writeback reverts the page in memory and drops the
refcount of each cluster allocated for it back to zero. The write may
still have partially reached the disk, so L1/L2 on disk may point to
such a cluster. If the page is not rewritten before suspend, the image
is left with a reference to a free cluster, which may also have been
reused for another offset meanwhile. Nothing reports that: L1/L2
writeback errors don't set MD_WRITEBACK_ERROR, as the revert is
considered safe.

Mark such a page with MD_LX_REVERTED and clear the mark on its next
successful writeback, which rewrites the whole page, e.g. when a
request delayed on ENOSPC is resubmitted. On md writeback flush a still
marked page sets a new lx_writeback_error flag, which is reported in
get_errors and included in wants_check, so resume is refused until the
image is checked and the target reloaded. The flush loop no longer
stops at the first page with MD_WRITEBACK_ERROR, so a marked page after
it is not missed.

https://virtuozzo.atlassian.net/browse/VSTOR-148171
Feature: dm-qcow2: block device over QCOW2 files driver

Signed-off-by: Alexander Ivanov <alexander.ivanov at virtuozzo.com>
---
 drivers/md/dm-qcow2-cmd.c    |  4 ++--
 drivers/md/dm-qcow2-map.c    |  3 +++
 drivers/md/dm-qcow2-target.c | 15 ++++++++++-----
 drivers/md/dm-qcow2.h        |  5 ++++-
 4 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/md/dm-qcow2-cmd.c b/drivers/md/dm-qcow2-cmd.c
index 28c2166fd47a..0f5d61f94f26 100644
--- a/drivers/md/dm-qcow2-cmd.c
+++ b/drivers/md/dm-qcow2-cmd.c
@@ -20,9 +20,9 @@ static int qcow2_get_errors(struct qcow2_target *tgt, char *result,
 	int ret;
 
 	ret = DMEMIT("wants_check=%d\nmd_writeback_error=%d\ntruncate_error=%d\n"
-		     "merge_backward_error=%d\n",
+		     "merge_backward_error=%d\nlx_writeback_error=%d\n",
 		      wants_check, tgt->md_writeback_error, tgt->truncate_error,
-		      tgt->backward_merge.error);
+		      tgt->backward_merge.error, tgt->lx_writeback_error);
 
 	return ret ? 1 : 0;
 }
diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
index 185243584e0c..1ecbb525b6aa 100644
--- a/drivers/md/dm-qcow2-map.c
+++ b/drivers/md/dm-qcow2-map.c
@@ -1362,6 +1362,7 @@ static void revert_l_entries_update(struct qcow2 *qcow2, struct wb_desc *wbd)
 		if (cleared)
 			continue; /* no cluster was allocated */
 
+		wbd->md->status |= MD_LX_REVERTED;
 		spin_unlock(&qcow2->md_pages_lock);
 		pos &= ~LX_REFCOUNT_EXACTLY_ONE;
 
@@ -1385,6 +1386,8 @@ static void clear_writeback_status(struct qcow2 *qcow2, struct md_page *md,
 	lockdep_assert_held(&qcow2->md_pages_lock);
 
 	md->status &= ~(MD_WRITEBACK|MD_WRITEBACK_ERROR);
+	if (!ret)
+		md->status &= ~MD_LX_REVERTED;
 	list_splice_init(&md->wait_list, wait_list);
 	if (ret && !md->wbd) {
 		/*
diff --git a/drivers/md/dm-qcow2-target.c b/drivers/md/dm-qcow2-target.c
index dc083572de5e..a9bdad198fde 100644
--- a/drivers/md/dm-qcow2-target.c
+++ b/drivers/md/dm-qcow2-target.c
@@ -170,6 +170,7 @@ static void qcow2_free_md_pages_tree(struct rb_root *root)
 void qcow2_flush_deferred_activity(struct qcow2_target *tgt, struct qcow2 *qcow2)
 {
 	struct rb_node *node;
+	bool wb_error = false;
 	struct md_page *md;
 	int i;
 
@@ -191,13 +192,17 @@ void qcow2_flush_deferred_activity(struct qcow2_target *tgt, struct qcow2 *qcow2
 	     node; node = rb_next(node)) {
 		md = rb_entry(node, struct md_page, node);
 		/* FIXME: call md_make_dirty() and try once again? */
-		if (md->status & MD_WRITEBACK_ERROR) {
-			QC_ERR(tgt->ti, "Failed to write dirty pages");
-			tgt->md_writeback_error = true;
-			break;
-		}
+		if (md->status & MD_WRITEBACK_ERROR)
+			wb_error = true;
+		if (md->status & MD_LX_REVERTED)
+			tgt->lx_writeback_error = true;
 	}
 	spin_unlock_irq(&qcow2->md_pages_lock);
+
+	if (wb_error) {
+		QC_ERR(tgt->ti, "Failed to write dirty pages");
+		tgt->md_writeback_error = true;
+	}
 }
 
 static void qcow2_flush_deferred_activity_all(struct qcow2_target *tgt)
diff --git a/drivers/md/dm-qcow2.h b/drivers/md/dm-qcow2.h
index 93c573c9a284..4113783b9d15 100644
--- a/drivers/md/dm-qcow2.h
+++ b/drivers/md/dm-qcow2.h
@@ -134,6 +134,7 @@ struct md_page {
 #define MD_DIRTY	(1U << 1) /* Page contains changes and wants writeback */
 #define MD_WRITEBACK	(1U << 2) /* Writeback was submitted */
 #define MD_WRITEBACK_ERROR (1U << 3) /* Last writeback failed with error */
+#define MD_LX_REVERTED	(1U << 4) /* L1/L2 on disk may point to freed cluster */
 	unsigned int status;
 	struct page *page;
 	struct list_head wait_list;
@@ -200,6 +201,7 @@ struct qcow2_target {
 	bool service_operations_allowed;
 	bool wants_suspend;
 	bool md_writeback_error;
+	bool lx_writeback_error;
 	bool truncate_error;
 	bool event_enospc;
 
@@ -461,7 +463,8 @@ static inline bool fake_service_qio(struct qio *qio)
 static inline bool qcow2_wants_check(struct qcow2_target *tgt)
 {
 
-	return !!(tgt->md_writeback_error|tgt->truncate_error);
+	return !!(tgt->md_writeback_error|tgt->lx_writeback_error|
+		  tgt->truncate_error);
 }
 
 static inline bool qcow2_file_is_writable(struct qcow2 *qcow2)
-- 
2.53.0