[Devel] [PATCH RHEL8 COMMIT] ploop: Check for activity being out of bio lists on destruction

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-80.1.2.vz8.3.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-80.1.2.vz8.3.3
------>
commit c3f36cd9fa1f357232638a0f132082b385d850d2
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Thu Mar 12 13:16:46 2020 +0300

    ploop: Check for activity being out of bio lists on destruction
    
    Queue ploop_inflight_bios_ref_switch() before flushing the queue
    to make inflight activity appear on delayed lists. Check the lists
    right after that.
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 drivers/md/dm-ploop-cmd.c    | 41 +++++++++++++++++++++++++++++++++++++++++
 drivers/md/dm-ploop-target.c | 26 ++++++++------------------
 drivers/md/dm-ploop.h        |  1 +
 3 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/drivers/md/dm-ploop-cmd.c b/drivers/md/dm-ploop-cmd.c
index 30fea812b9c0..a6597f573151 100644
--- a/drivers/md/dm-ploop-cmd.c
+++ b/drivers/md/dm-ploop-cmd.c
@@ -1625,6 +1625,43 @@ static int ploop_push_backup_write(struct ploop *ploop, char *uuid,
 	return 0;
 }
 
+static bool ploop_has_pending_activity(struct ploop *ploop)
+{
+	bool has;
+
+	spin_lock_irq(&ploop->deferred_lock);
+	has = ploop->deferred_cmd;
+	has |= !bio_list_empty(&ploop->deferred_bios);
+	has |= !bio_list_empty(&ploop->discard_bios);
+	has |= !bio_list_empty(&ploop->delta_cow_action_list);
+	spin_unlock_irq(&ploop->deferred_lock);
+
+	return has;
+}
+
+static void process_try_preflush(struct ploop *ploop, struct ploop_cmd *cmd)
+{
+	/* Make all inflight bios appear in pending activities */
+	cmd->retval = ploop_inflight_bios_ref_switch(ploop, true);
+	if (!cmd->retval)
+		cmd->retval = ploop_has_pending_activity(ploop);
+	complete(&cmd->comp); /* Last touch of cmd memory */
+}
+
+static int ploop_try_preflush(struct ploop *ploop)
+{
+	struct ploop_cmd cmd = { {0} };
+
+	cmd.type = PLOOP_CMD_TRY_PREFLUSH;
+	cmd.ploop = ploop;
+
+	init_completion(&cmd.comp);
+	ploop_queue_deferred_cmd(ploop, &cmd);
+	wait_for_completion(&cmd.comp);
+	return cmd.retval;
+
+}
+
 /* Handle user commands requested via "message" interface */
 void process_deferred_cmd(struct ploop *ploop, struct ploop_index_wb *piwb)
 	__releases(&ploop->deferred_lock)
@@ -1659,6 +1696,8 @@ void process_deferred_cmd(struct ploop *ploop, struct ploop_index_wb *piwb)
 		process_flip_upper_deltas(ploop, cmd);
 	} else if (cmd->type == PLOOP_CMD_SET_PUSH_BACKUP) {
 		process_set_push_backup(ploop, cmd);
+	} else if (cmd->type == PLOOP_CMD_TRY_PREFLUSH) {
+		process_try_preflush(ploop, cmd);
 	} else {
 		cmd->retval = -EINVAL;
 		complete(&cmd->comp);
@@ -1763,6 +1802,8 @@ int ploop_message(struct dm_target *ti, unsigned int argc, char **argv,
 		if (argc != 3 || sscanf(argv[2], "%llu:%llu", &val, &val2) != 2)
 			goto unlock;
 		ret = ploop_push_backup_write(ploop, argv[1], val, val2);
+	} else if (!strcmp(argv[0], "try_preflush")) {
+		ret = ploop_try_preflush(ploop);
 	} else {
 		ret = -ENOTSUPP;
 	}
diff --git a/drivers/md/dm-ploop-target.c b/drivers/md/dm-ploop-target.c
index 318048227f53..d36906793b9f 100644
--- a/drivers/md/dm-ploop-target.c
+++ b/drivers/md/dm-ploop-target.c
@@ -29,33 +29,23 @@ static void inflight_bios_ref_exit1(struct percpu_ref *ref)
 	complete(&ploop->inflight_bios_ref_comp);
 }
 
-static bool ploop_has_pending_activity(struct ploop *ploop)
-{
-	bool has;
-
-	spin_lock_irq(&ploop->deferred_lock);
-	has = ploop->deferred_cmd;
-	has |= !bio_list_empty(&ploop->deferred_bios);
-	has |= !bio_list_empty(&ploop->discard_bios);
-	has |= !bio_list_empty(&ploop->delta_cow_action_list);
-	spin_unlock_irq(&ploop->deferred_lock);
-
-	return has;
-}
-
+/* This is called on final device destroy */
 static void ploop_flush_workqueue(struct ploop *ploop)
 {
+	char *argv[1] = {"try_preflush"};
 	bool again = true;
 
 	while (again) {
 		flush_workqueue(ploop->wq);
-		again = ploop_has_pending_activity(ploop);
-		if (again)
-			schedule_timeout(HZ);
+		/*
+		 * Normally, ploop_message("try_preflush") returns 0 or 1.
+		 * In case of underlining bdev is hung, this finishes with
+		 * error by timeout, and our caller (.dtr) never completes.
+		 */
+		again = ploop_message(ploop->ti, 1, argv, NULL, 0);
 	}
 }
 
-
 static void ploop_destroy(struct ploop *ploop)
 {
 	int i;
diff --git a/drivers/md/dm-ploop.h b/drivers/md/dm-ploop.h
index 3b0a96da837f..52b66440f066 100644
--- a/drivers/md/dm-ploop.h
+++ b/drivers/md/dm-ploop.h
@@ -46,6 +46,7 @@ struct ploop_cmd {
 #define PLOOP_CMD_TRACKING_START	7
 #define PLOOP_CMD_FLIP_UPPER_DELTAS	8
 #define PLOOP_CMD_SET_PUSH_BACKUP	9
+#define PLOOP_CMD_TRY_PREFLUSH		10
 	struct completion comp;
 	struct ploop *ploop;
 	unsigned int type;