[PATCH 1/3] z3fold: simplify freeing slots

[Vitaly Wool <vitaly.wool@konsulko.com>]

There used to be two places in the code where slots could be freed,
namely when freeing the last allocated handle from the slots and
when releasing the z3fold header these slots aree linked to. The
logic to decide on whether to free certain slots was complicated
and error prone in both functions and it led to failures in RT case.

To fix that, make free_handle() the single point of freeing slots.

Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
Tested-by: Mike Galbraith <efault@gmx.de>
Cc: stable@kernel.org
---
 mm/z3fold.c | 55 +++++++++++++----------------------------------------
 1 file changed, 13 insertions(+), 42 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 18feaa0bc537..6c2325cd3fba 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -90,7 +90,7 @@ struct z3fold_buddy_slots {
 	 * be enough slots to hold all possible variants
 	 */
 	unsigned long slot[BUDDY_MASK + 1];
-	unsigned long pool; /* back link + flags */
+	unsigned long pool; /* back link */
 	rwlock_t lock;
 };
 #define HANDLE_FLAG_MASK	(0x03)
@@ -181,13 +181,6 @@ enum z3fold_page_flags {
 	PAGE_CLAIMED, /* by either reclaim or free */
 };
 
-/*
- * handle flags, go under HANDLE_FLAG_MASK
- */
-enum z3fold_handle_flags {
-	HANDLES_ORPHANED = 0,
-};
-
 /*
  * Forward declarations
  */
@@ -303,10 +296,9 @@ static inline void put_z3fold_header(struct z3fold_header *zhdr)
 		z3fold_page_unlock(zhdr);
 }
 
-static inline void free_handle(unsigned long handle)
+static inline void free_handle(unsigned long handle, struct z3fold_header *zhdr)
 {
 	struct z3fold_buddy_slots *slots;
-	struct z3fold_header *zhdr;
 	int i;
 	bool is_free;
 
@@ -316,22 +308,13 @@ static inline void free_handle(unsigned long handle)
 	if (WARN_ON(*(unsigned long *)handle == 0))
 		return;
 
-	zhdr = handle_to_z3fold_header(handle);
 	slots = handle_to_slots(handle);
 	write_lock(&slots->lock);
 	*(unsigned long *)handle = 0;
-	if (zhdr->slots == slots) {
-		write_unlock(&slots->lock);
-		return; /* simple case, nothing else to do */
-	}
+	if (zhdr->slots != slots)
+		zhdr->foreign_handles--;
 
-	/* we are freeing a foreign handle if we are here */
-	zhdr->foreign_handles--;
 	is_free = true;
-	if (!test_bit(HANDLES_ORPHANED, &slots->pool)) {
-		write_unlock(&slots->lock);
-		return;
-	}
 	for (i = 0; i <= BUDDY_MASK; i++) {
 		if (slots->slot[i]) {
 			is_free = false;
@@ -343,6 +326,8 @@ static inline void free_handle(unsigned long handle)
 	if (is_free) {
 		struct z3fold_pool *pool = slots_to_pool(slots);
 
+		if (zhdr->slots == slots)
+			zhdr->slots = NULL;
 		kmem_cache_free(pool->c_handle, slots);
 	}
 }
@@ -525,8 +510,6 @@ static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 {
 	struct page *page = virt_to_page(zhdr);
 	struct z3fold_pool *pool = zhdr_to_pool(zhdr);
-	bool is_free = true;
-	int i;
 
 	WARN_ON(!list_empty(&zhdr->buddy));
 	set_bit(PAGE_STALE, &page->private);
@@ -536,21 +519,6 @@ static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 		list_del_init(&page->lru);
 	spin_unlock(&pool->lock);
 
-	/* If there are no foreign handles, free the handles array */
-	read_lock(&zhdr->slots->lock);
-	for (i = 0; i <= BUDDY_MASK; i++) {
-		if (zhdr->slots->slot[i]) {
-			is_free = false;
-			break;
-		}
-	}
-	if (!is_free)
-		set_bit(HANDLES_ORPHANED, &zhdr->slots->pool);
-	read_unlock(&zhdr->slots->lock);
-
-	if (is_free)
-		kmem_cache_free(pool->c_handle, zhdr->slots);
-
 	if (locked)
 		z3fold_page_unlock(zhdr);
 
@@ -973,6 +941,9 @@ static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
 		}
 	}
 
+	if (zhdr && !zhdr->slots)
+		zhdr->slots = alloc_slots(pool,
+					can_sleep ? GFP_NOIO : GFP_ATOMIC);
 	return zhdr;
 }
 
@@ -1270,7 +1241,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 	}
 
 	if (!page_claimed)
-		free_handle(handle);
+		free_handle(handle, zhdr);
 	if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
 		atomic64_dec(&pool->pages_nr);
 		return;
@@ -1429,19 +1400,19 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 			ret = pool->ops->evict(pool, middle_handle);
 			if (ret)
 				goto next;
-			free_handle(middle_handle);
+			free_handle(middle_handle, zhdr);
 		}
 		if (first_handle) {
 			ret = pool->ops->evict(pool, first_handle);
 			if (ret)
 				goto next;
-			free_handle(first_handle);
+			free_handle(first_handle, zhdr);
 		}
 		if (last_handle) {
 			ret = pool->ops->evict(pool, last_handle);
 			if (ret)
 				goto next;
-			free_handle(last_handle);
+			free_handle(last_handle, zhdr);
 		}
 next:
 		if (test_bit(PAGE_HEADLESS, &page->private)) {
-- 
2.20.1