[Devel] [RFC PATCH vz9 v6 59/62] 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.

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 | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index a03e1af3fd87..482022d6b60b 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -1312,24 +1312,31 @@ 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;
+
+				PL_ERR("ret = 0 bi_size=%d\n", pio->bi_iter.bi_size);
+				synchronize_rcu();
+				ploop_queue_resubmit(pio);
+			}
+
 			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);
 		pio->bi_status = errno_to_blk_status(pio->ret);
 	}
-check_da:
 	if (pio->is_data_alloc) {
 		completed = ploop_data_pio_end(pio);
 		if (!completed)
-- 
2.43.0