[Devel] [PATCH hci-8.1 2/2] dm-ploop: fix the ENOSPC retry timer not waking the dispatcher

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

A write that fails with ENOSPC on the image is held on enospc_pios and
retried when enospc_timer fires, so that I/O resumes once space is
freed. ploop_enospc_timer() only sets submit_enospc, which only
do_ploop_run_work() consumes, and nothing wakes the dispatcher for it.
ploop_worker() also goes to sleep with the flag set, as its sleep
condition checks the pio lists only. The held writes are retried only
when other I/O reaches the device: on a device whose only I/O is the
held writes, the writers stay in D state after the space is freed.

Wake the dispatcher from the timer, and keep ploop_worker() awake while
submit_enospc is set, so that a wakeup that comes while the dispatcher
is busy is not lost. Test and clear the flag with xchg() in
do_ploop_run_work(), as the timer now sets it from another CPU.

https://virtuozzo.atlassian.net/browse/VSTOR-154182

Fixes: afc60480b037 ("dm-ploop: resubmit enospc pios from dispatcher thread")
Feature: dm-ploop: ploop target driver
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 drivers/md/dm-ploop-map.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index ae3e287604b7..a4e17aa090a6 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -165,7 +165,9 @@ static void ploop_init_prq_and_embedded_pio(struct ploop *ploop,
 void ploop_enospc_timer(struct timer_list *timer)
 {
 	struct ploop *ploop = timer_container_of(ploop, timer, enospc_timer);
-	ploop->submit_enospc = true;
+
+	WRITE_ONCE(ploop->submit_enospc, true);
+	wake_up_process(ploop->kt_worker->task);
 }
 
 void do_ploop_event_work(struct work_struct *ws)
@@ -2241,10 +2243,8 @@ static void do_ploop_run_work(struct ploop *ploop)
 
 	current->flags |= PLOOP_PFLAGS;
 
-	if (ploop->submit_enospc) {
-		ploop->submit_enospc = false;
+	if (xchg(&ploop->submit_enospc, false))
 		ploop_resubmit_enospc_pios(ploop);
-	}
 
 	llembedded_pios = llist_del_all(&ploop->pios[PLOOP_LIST_PREPARE]);
 
@@ -2447,6 +2447,7 @@ int ploop_worker(void *data)
 		    llist_empty(&ploop->pios[PLOOP_LIST_DISCARD]) &&
 		    llist_empty(&ploop->pios[PLOOP_LIST_COW]) &&
 		    llist_empty(&ploop->llresubmit_pios) &&
+		    !READ_ONCE(ploop->submit_enospc) &&
 		    !ploop->force_md_writeback) {
 			if (kthread_should_stop()) {
 				wait_event_interruptible(
-- 
2.53.0

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