[Devel] [PATCH hci-8.1 v11 09/10] dm-qcow2: retry R1/R2 writeback that failed with ENOSPC

[Alexander Ivanov <alexander.ivanov@virtuozzo.com>]

A failed R1/R2 writeback sets MD_WRITEBACK_ERROR and drops MD_DIRTY.
Nothing writes the page again unless its refcounts change. On suspend
the md writeback flush finds the error and sets md_writeback_error, so
resume is refused until the image is checked and the target reloaded,
even if the failure was a transient ENOSPC of the underlying fs and
the space has been freed since.

Redirty the page on -ENOSPC, so the slow writeback timer retries it,
as data writes delayed on ENOSPC are retried. Flushing deferred md
activity on suspend, merge and target destruction fires the timer,
which gives the page one more try. A page that still fails then is not
redirtied, so no timer is left armed after the flush, before the image
is freed, and md_writeback_error is set as before.

complete_metadata_writeback() turned every failed write into -EIO.
Pass the errno of the write through and keep -EIO for a short write.
A data request depending on a failed L1/L2 write then ends with
BLK_STS_NOSPC and is delayed and resubmitted like any other write
failing with ENOSPC, as already happens when fsync fails with it.

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

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
---
 drivers/md/dm-qcow2-map.c    | 6 ++++--
 drivers/md/dm-qcow2-target.c | 4 +++-
 drivers/md/dm-qcow2.h        | 1 +
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
index 4ab8051f08c4..3bcaceab1a1d 100644
--- a/drivers/md/dm-qcow2-map.c
+++ b/drivers/md/dm-qcow2-map.c
@@ -1357,6 +1357,8 @@ static void clear_writeback_status(struct qcow2 *qcow2, struct md_page *md,
 		 * so here we care about R1R2 only.
 		 */
 		md->status |= MD_WRITEBACK_ERROR;
+		if (ret == -ENOSPC && !READ_ONCE(qcow2->md_wb_no_retry))
+			qcow2_md_make_dirty(qcow2, md, true);
 	}
 	if (md->wbd) {
 		if (likely(ret == 0))
@@ -3867,9 +3869,9 @@ static int complete_metadata_writeback(struct qcow2 *qcow2)
 		md = qio->ext->md;
 		qvec = qio->data;
 		ret = qio->ret;
-		if (unlikely(ret != PAGE_SIZE))
+		if (unlikely(ret >= 0 && ret != PAGE_SIZE))
 			ret = -EIO;
-		else
+		else if (ret == PAGE_SIZE)
 			ret = fsync_ret;
 
 		do_md_page_write_complete(ret, qcow2, md);
diff --git a/drivers/md/dm-qcow2-target.c b/drivers/md/dm-qcow2-target.c
index 99fb68a5535e..e28c47d4e728 100644
--- a/drivers/md/dm-qcow2-target.c
+++ b/drivers/md/dm-qcow2-target.c
@@ -173,7 +173,9 @@ void qcow2_flush_deferred_activity(struct qcow2_target *tgt, struct qcow2 *qcow2
 	struct md_page *md;
 	int i;
 
+	/* Retry R1/R2 writeback failed with ENOSPC once, then give up */
 	for (i = 0; i < 2; i++) {
+		WRITE_ONCE(qcow2->md_wb_no_retry, i == 1);
 		if (timer_delete_sync_try(&qcow2->slow_wb_timer) != -1)
 			qcow2_slow_wb_timer_fn(&qcow2->slow_wb_timer);
 		/* Start md writeback */
@@ -181,12 +183,12 @@ void qcow2_flush_deferred_activity(struct qcow2_target *tgt, struct qcow2 *qcow2
 		/* Wait AIO of md wb */
 		qcow2_inflight_ref_switch(tgt);
 	}
+	WRITE_ONCE(qcow2->md_wb_no_retry, false);
 
 	spin_lock_irq(&qcow2->md_pages_lock);
 	for (node = rb_first(&qcow2->md_pages);
 	     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;
diff --git a/drivers/md/dm-qcow2.h b/drivers/md/dm-qcow2.h
index 2a6203c86e3a..ebab22d505e8 100644
--- a/drivers/md/dm-qcow2.h
+++ b/drivers/md/dm-qcow2.h
@@ -281,6 +281,7 @@ struct qcow2 {
 	struct list_head wb_batch_list;
 	struct list_head slow_wb_batch_list;
 	struct timer_list slow_wb_timer;
+	bool md_wb_no_retry;
 
 	struct work_struct worker;
 	struct work_struct fsync_worker;
-- 
2.53.0

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