[Devel] [RFC PATCH vz9 v5 49/49] dm-ploop: disable fast path

[Alexander Atanasov]

*** JUST FOR TESTING - NOT TO BE APPLIED  ***

Fast path results in rcu lockups and hangs.
The reason is that we got called from fs,
then we try to re-enter the fs but fs is not ready for this.

There is an idea to investigate - try to skip dispatcher thread
and directly execute in a runner thread.

Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
---
 drivers/md/dm-ploop-map.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index dc9fb36ded3f..9ffe41fa4c02 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -2308,8 +2308,14 @@ static void ploop_submit_embedded_pio(struct ploop *ploop, struct pio *pio)
 	}
 
 	ploop_prepare_one_embedded_pio(ploop, pio, &deferred_pios);
-	/* check if result is a single pio , so we can try fast path */
-	if (deferred_pios.first && deferred_pios.first->next == NULL) {
+	/*
+	 * Disable fast path due to rcu lockups fs -> ploop -> fs - fses are not reentrant
+	 * we can however try another fast path skip dispatcher thread and pass directly to
+	 * runners
+	 */
+#define ENABLE_FAST_PATH 0
+	/* check if result is a single pio, if so we can try fast path */
+	if (ENABLE_FAST_PATH && deferred_pios.first && deferred_pios.first->next == NULL) {
 		spio = list_entry((struct list_head *)deferred_pios.first, typeof(*spio), list);
 		INIT_LIST_HEAD(&spio->list);
 		if (req_op(rq) == REQ_OP_READ) {
-- 
2.43.0