bcachefs: Fix for spinning in journal reclaim on startup

We normally avoid having too many dirty keys in the btree key cache, to
ensure that we can always shrink our caches to reclaim memory if needed.

But this check was causing us to go into an infinite loop on startup, in
the btree insert path before journal reclaim was started.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_key_cache.h

@@ -16,7 +16,8 @@ static inline bool bch2_btree_key_cache_must_wait(struct bch_fs *c)
 	size_t nr_keys = READ_ONCE(c->btree_key_cache.nr_keys);
 	size_t max_dirty = 4096 + (nr_keys * 3) / 4;
 
-	return nr_dirty > max_dirty;
+	return nr_dirty > max_dirty &&
+		test_bit(JOURNAL_RECLAIM_STARTED, &c->journal.flags);
 }
 
 struct bkey_cached *