bcachefs: Fix for copygc getting stuck waiting for reserve to be filled

This fixes a regression from the patch
  bcachefs: Fix copygc dying on startup

In general only the allocator thread itself should be updating
ca->allocator_state, the thread waking up the allocator setting it is an
ugly hack only needed to avoid racing with the copygc threads when we're
first starting up.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/alloc_background.h

@@ -100,10 +100,8 @@ static inline void bch2_wake_allocator(struct bch_dev *ca)
 
 	rcu_read_lock();
 	p = rcu_dereference(ca->alloc_thread);
-	if (p) {
+	if (p)
 		wake_up_process(p);
-		ca->allocator_state = ALLOCATOR_running;
-	}
 	rcu_read_unlock();
 }
 

fs/bcachefs/super.c

@@ -908,9 +908,16 @@ int bch2_fs_start(struct bch_fs *c)
 	/*
 	 * Allocator threads don't start filling copygc reserve until after we
 	 * set BCH_FS_STARTED - wake them now:
+	 *
+	 * XXX ugly hack:
+	 * Need to set ca->allocator_state here instead of relying on the
+	 * allocator threads to do it to avoid racing with the copygc threads
+	 * checking it and thinking they have no alloc reserve:
 	 */
-	for_each_online_member(ca, c, i)
+	for_each_online_member(ca, c, i) {
+		ca->allocator_state = ALLOCATOR_running;
 		bch2_wake_allocator(ca);
+	}
 
 	if (c->opts.read_only || c->opts.nochanges) {
 		bch2_fs_read_only(c);