six locks: Kill six_lock_pcpu_(alloc|free)

six_lock_pcpu_alloc() is an unsafe interface: it's not safe to allocate
or free the percpu reader count on an existing lock that's in use, the
only safe time to allocate percpu readers is when the lock is first
being initialized.

This patch adds a flags parameter to six_lock_init(), and instead of
six_lock_pcpu_free() we now expose six_lock_exit(), which does the same
thing but is less likely to be misused.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 4 insertions, 9 deletions

diff --git a/fs/bcachefs/btree_key_cache.c b/fs/bcachefs/btree_key_cache.c
index 727ea2d0e58d..9725d85b99b3 100644
--- a/fs/bcachefs/btree_key_cache.c
+++ b/fs/bcachefs/btree_key_cache.c
@@ -282,9 +282,7 @@ bkey_cached_alloc(struct btree_trans *trans, struct btree_path *path,
 		return NULL;
 init:
 	INIT_LIST_HEAD(&ck->list);
-	bch2_btree_lock_init(&ck->c);
-	if (pcpu_readers)
-		six_lock_pcpu_alloc(&ck->c.lock);
+	bch2_btree_lock_init(&ck->c, pcpu_readers ? SIX_LOCK_INIT_PCPU : 0);
 
 	ck->c.cached = true;
 	BUG_ON(!six_trylock_intent(&ck->c.lock));
@@ -340,9 +338,6 @@ btree_key_cache_create(struct btree_trans *trans, struct btree_path *path)
 		}
 
 		mark_btree_node_locked(trans, path, 0, SIX_LOCK_intent);
-	} else {
-		if (path->btree_id == BTREE_ID_subvolumes)
-			six_lock_pcpu_alloc(&ck->c.lock);
 	}
 
 	ck->c.level		= 0;
@@ -871,7 +866,7 @@ static unsigned long bch2_btree_key_cache_scan(struct shrinker *shrink,
 			break;
 
 		list_del(&ck->list);
-		six_lock_pcpu_free(&ck->c.lock);
+		six_lock_exit(&ck->c.lock);
 		kmem_cache_free(bch2_key_cache, ck);
 		atomic_long_dec(&bc->nr_freed);
 		scanned++;
@@ -887,7 +882,7 @@ static unsigned long bch2_btree_key_cache_scan(struct shrinker *shrink,
 			break;
 
 		list_del(&ck->list);
-		six_lock_pcpu_free(&ck->c.lock);
+		six_lock_exit(&ck->c.lock);
 		kmem_cache_free(bch2_key_cache, ck);
 		atomic_long_dec(&bc->nr_freed);
 		scanned++;
@@ -1012,7 +1007,7 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc)
 
 		list_del(&ck->list);
 		kfree(ck->k);
-		six_lock_pcpu_free(&ck->c.lock);
+		six_lock_exit(&ck->c.lock);
 		kmem_cache_free(bch2_key_cache, ck);
 	}