[Devel] [PATCH vz9 v1 53/63] dm-ploop: fix how ENOTBLK is handled

[Alexander Atanasov]

direct IO  write result ENOTBLK or 0(in ext4 case) means
retry IO in buffered mode. We wrongly assumed that it is
a short write and handled it incorrectly

Since we can not retry in buffered mode, code is not ready
for it. Take a different route. This error happens if
page invalidation fails, which is a very rare situation.
So call synchronize_rcu() and just resubmit pio.
Try this three times and end pio with error.

https://virtuozzo.atlassian.net/browse/VSTOR-91821
Suggested-by: Alexey Kuznetsov <kuznet at virtuozzo.com>
Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
---
 drivers/md/dm-ploop-map.c | 31 +++++++++++++++++++++++--------
 drivers/md/dm-ploop.h     |  1 +
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index dc150c8050d9..7d5e2cf443ee 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -94,6 +94,7 @@ void ploop_init_pio(struct ploop *ploop, unsigned int bi_op, struct pio *pio)
 	/* FIXME: assign real clu? */
 	pio->clu = UINT_MAX;
 	pio->level = BAT_LEVEL_INVALID;
+	pio->retries = 0;
 }
 
 /* Check that rq end byte is not behind end of device */
@@ -1322,18 +1323,32 @@ static void ploop_data_rw_complete(struct pio *pio)
 	bool completed;
 
 	if (pio->ret != pio->bi_iter.bi_size) {
-		if (pio->ret >= 0) {
-			/* Partial IO */
-			WARN_ON_ONCE(pio->ret == 0);
-			/* Do not resubmit zero length pio */
+		if (pio->ret >= 0 || pio->ret == -ENOTBLK) {
+			/* Partial IO or request to retry in buffered mode */
+			if (pio->ret == 0 || pio->ret == -ENOTBLK) {
+				/*
+				 * ENOTBLK means we should retry in buffered io
+				 * but we can not, so try again in DIO
+				 * ext4 returns 0 for ENOTBLK
+				 */
+				struct ploop *ploop = pio->ploop;
+
+				if (pio->retries++ < 3) {
+					PL_ERR("ret = 0 bi_size=%d\n", pio->bi_iter.bi_size);
+					synchronize_rcu();
+					ploop_queue_resubmit(pio);
+				} else {
+					/* we retried but still failed */
+					pio->bi_status = BLK_STS_IOERR;
+					goto check_da;
+				}
+			}
+
 			if (pio->ret > 0) {
 				ploop_pio_advance(pio, pio->ret);
 				ploop_queue_resubmit(pio);
-				return;
-			} else {
-				pio->bi_status = BLK_STS_IOERR;
-				goto check_da;
 			}
+			return;
 		}
 		if (static_branch_unlikely(&ploop_standby_check))
 			ploop_check_standby_mode(pio->ploop, pio->ret);
diff --git a/drivers/md/dm-ploop.h b/drivers/md/dm-ploop.h
index 9f193afab618..11e50ab1293b 100644
--- a/drivers/md/dm-ploop.h
+++ b/drivers/md/dm-ploop.h
@@ -315,6 +315,7 @@ struct pio {
 	unsigned int		runner_id;
 
 	atomic_t md_inflight;
+	unsigned char retries;
 };
 
 /* Delta COW private */
-- 
2.43.0