[Devel] [RFC PATCH vz9 v4 33/33] dm-ploop: convert wb_batch_list to lockless variant

[Alexander Atanasov]

Merging required to back this change, so do it again.

Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
---
 drivers/md/dm-ploop-map.c | 49 ++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 24 deletions(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index 621a952ef32c..6cab948dfa29 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -562,7 +562,7 @@ static bool ploop_md_make_dirty(struct ploop *ploop, struct md_page *md)
 	WARN_ON_ONCE(test_bit(MD_WRITEBACK, &md->status));
 	md->dirty_time = ktime_get();
 	if (!test_and_set_bit(MD_DIRTY, &md->status)) {
-		list_add(&md->wb_link, &ploop->wb_batch_list);
+		llist_add((struct llist_node *)&md->wb_link, &ploop->wb_batch_llist);
 		new = true;
 	}
 	write_unlock_irqrestore(&ploop->bat_rwlock, flags);
@@ -1831,36 +1831,36 @@ static void ploop_submit_metadata_writeback(struct ploop *ploop)
 {
 	ktime_t ktime, ktimeout;
 	LIST_HEAD(ll_skipped);
-	struct md_page *md, *mtmp;
+	struct md_page *md;
+	struct llist_node *pos, *t;
+	struct llist_node *ll_wb_batch;
 
 	ktime = ktime_get();
 	ktimeout = ktime_add_ms(ktime, ploop->md_submit_delay_ms);
+	/* Lock here to protect against md_inflight counting */
+	write_lock_irq(&ploop->bat_rwlock);
+	ll_wb_batch = llist_del_all(&ploop->wb_batch_llist);
+	write_unlock_irq(&ploop->bat_rwlock);
 	/*
 	 * Pages are set dirty so no one must touch lists
 	 * if new md entries are dirtied they are added at the start of the list
 	 */
-	list_for_each_entry_safe(md, mtmp, &ploop->wb_batch_list, wb_link) {
-		write_lock_irq(&ploop->bat_rwlock);
-		list_del_init(&md->wb_link);
+	llist_for_each_safe(pos, t, ll_wb_batch ) {
+		md = list_entry((struct list_head *)pos, typeof(*md), wb_link);
+		INIT_LIST_HEAD(&md->wb_link);
 		if (md->high_prio || ktime_after(md->dirty_time, ktimeout)
 		    || ploop->force_md_writeback) {
 			/* L1L2 mustn't be redirtyed, when wb in-flight! */
 			WARN_ON_ONCE(!test_bit(MD_DIRTY, &md->status));
 			WARN_ON_ONCE(test_bit(MD_WRITEBACK, &md->status));
+			md->high_prio = false;
 			set_bit(MD_WRITEBACK, &md->status);
 			clear_bit(MD_DIRTY, &md->status);
-			md->high_prio = false;
-			write_unlock_irq(&ploop->bat_rwlock);
 			ploop_index_wb_submit(ploop, md->piwb);
 		} else {
-			list_add_tail(&md->wb_link, &ll_skipped);
-			write_unlock_irq(&ploop->bat_rwlock);
+			llist_add((struct llist_node *)&md->wb_link, &ploop->wb_batch_llist);
 		}
 	}
-	write_lock_irq(&ploop->bat_rwlock);
-	list_splice(&ll_skipped, &ploop->wb_batch_list);
-	write_unlock_irq(&ploop->bat_rwlock);
-
 }
 
 static void process_ploop_fsync_work(struct ploop *ploop, struct llist_node *llflush_pios)
@@ -1993,18 +1993,19 @@ static void ploop_preflush_endio(struct pio *pio, void *orig_pio_ptr,
 	}
 }
 
-static void ploop_prepare_flush(struct ploop *ploop, struct pio *pio)
+static int ploop_prepare_flush(struct ploop *ploop, struct pio *pio)
 {
 	struct pio *flush_pio = pio;
 	struct md_page *md, *n;
 	int md_inflight = 0;
+	struct llist_node *pos, *t;
 
 	if (pio->bi_op & REQ_PREFLUSH && (pio->bi_op & REQ_OP_MASK) != REQ_OP_FLUSH) {
 		flush_pio = ploop_alloc_pio(ploop, GFP_NOIO);
 		if (!flush_pio) {
 			pio->bi_status = BLK_STS_RESOURCE;
 			ploop_pio_endio(pio);
-			return;
+			return -1;
 		}
 
 		ploop_init_pio(ploop, REQ_OP_FLUSH, flush_pio);
@@ -2015,21 +2016,17 @@ static void ploop_prepare_flush(struct ploop *ploop, struct pio *pio)
 	}
 
 	write_lock_irq(&ploop->bat_rwlock);
-
-	list_for_each_entry_safe(md, n, &ploop->wb_batch_list, wb_link) {
+	llist_for_each_safe(pos, t, ploop->wb_batch_llist.first) {
+		md = list_entry((struct list_head *)pos, typeof(*md), wb_link);
 		md_inflight++;
 		md->piwb->flush_pio = flush_pio;
 		md->high_prio = true;
 	}
 
 	atomic_set(&flush_pio->md_inflight, md_inflight);
-
 	write_unlock_irq(&ploop->bat_rwlock);
 
-	if (md_inflight)
-		ploop_schedule_work(ploop);
-	else
-		ploop_dispatch_pios(ploop, flush_pio, NULL);
+	return md_inflight;
 }
 
 static void ploop_submit_embedded_pio(struct ploop *ploop, struct pio *pio)
@@ -2058,8 +2055,12 @@ static void ploop_submit_embedded_pio(struct ploop *ploop, struct pio *pio)
 	ploop_inc_nr_inflight(ploop, pio);
 
 	if ((pio->bi_op & REQ_OP_MASK) == REQ_OP_FLUSH || pio->bi_op & REQ_PREFLUSH) {
-		ploop_prepare_flush(ploop, pio);
-		return;
+		ret = ploop_prepare_flush(ploop, pio);
+		if (ret < 0)
+			return;
+		if (ret > 0)
+			goto out;
+		/* Will add to prepare list and schedule work */
 	}
 
 	if (pio->queue_list_id == PLOOP_LIST_FLUSH) {
-- 
2.43.0