[PATCH -next v4 3/6] Revert "frontswap: simplify frontswap_register_ops"

[Liu Shixin]

This reverts commit f328c1d16e4c764992895ac9c9425cea861b2ca0.

Since we are supported to delay zswap initializaton, we need to invoke
ops->init for the swap device which is already online when register
backend.

Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
 mm/frontswap.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 8d644f56a1d2..555e78f9529d 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -99,6 +99,25 @@ static inline void inc_frontswap_invalidates(void) { }
  */
 void frontswap_register_ops(struct frontswap_ops *ops)
 {
+	DECLARE_BITMAP(a, MAX_SWAPFILES);
+	DECLARE_BITMAP(b, MAX_SWAPFILES);
+	struct swap_info_struct *si;
+	unsigned int i;
+
+	bitmap_zero(a, MAX_SWAPFILES);
+	bitmap_zero(b, MAX_SWAPFILES);
+
+	spin_lock(&swap_lock);
+	plist_for_each_entry(si, &swap_active_head, list) {
+		if (!WARN_ON(!si->frontswap_map))
+			__set_bit(si->type, a);
+	}
+	spin_unlock(&swap_lock);
+
+	/* the new ops needs to know the currently active swap devices */
+	for_each_set_bit(i, a, MAX_SWAPFILES)
+		ops->init(i);
+
 	/*
 	 * Setting frontswap_ops must happen after the ops->init() calls
 	 * above; cmpxchg implies smp_mb() which will ensure the init is
@@ -109,6 +128,28 @@ void frontswap_register_ops(struct frontswap_ops *ops)
 	} while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
 
 	static_branch_inc(&frontswap_enabled_key);
+
+	spin_lock(&swap_lock);
+	plist_for_each_entry(si, &swap_active_head, list) {
+		if (si->frontswap_map)
+			__set_bit(si->type, b);
+	}
+	spin_unlock(&swap_lock);
+
+	/*
+	 * On the very unlikely chance that a swap device was added or
+	 * removed between setting the "a" list bits and the ops init
+	 * calls, we re-check and do init or invalidate for any changed
+	 * bits.
+	 */
+	if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) {
+		for (i = 0; i < MAX_SWAPFILES; i++) {
+			if (!test_bit(i, a) && test_bit(i, b))
+				ops->init(i);
+			else if (test_bit(i, a) && !test_bit(i, b))
+				ops->invalidate_area(i);
+		}
+	}
 }
 
 /*
-- 
2.25.1