bcachefs: Don't downgrade locks on transaction restart

We should only be downgrading locks on success - otherwise, our
transaction restarts won't be getting the correct locks and we'll
livelock.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -1523,6 +1523,7 @@ static inline struct btree_path *btree_path_alloc(struct btree_trans *trans,
 	path->ref		= 0;
 	path->intent_ref	= 0;
 	path->nodes_locked	= 0;
+	path->alloc_seq++;
 
 	btree_path_list_add(trans, pos, path);
 	trans->paths_sorted = false;
@@ -1598,7 +1599,7 @@ struct btree_path *bch2_path_get(struct btree_trans *trans,
 
 	locks_want = min(locks_want, BTREE_MAX_DEPTH);
 	if (locks_want > path->locks_want)
-		bch2_btree_path_upgrade_noupgrade_sibs(trans, path, locks_want);
+		bch2_btree_path_upgrade_noupgrade_sibs(trans, path, locks_want, NULL);
 
 	return path;
 }

fs/bcachefs/btree_key_cache.c

@@ -509,7 +509,7 @@ bch2_btree_path_traverse_cached_slowpath(struct btree_trans *trans, struct btree
 		 * path->uptodate yet:
 		 */
 		if (!path->locks_want &&
-		    !__bch2_btree_path_upgrade(trans, path, 1)) {
+		    !__bch2_btree_path_upgrade(trans, path, 1, NULL)) {
 			trace_and_count(trans->c, trans_restart_key_cache_upgrade, trans, _THIS_IP_);
 			ret = btree_trans_restart(trans, BCH_ERR_transaction_restart_key_cache_upgrade);
 			goto err;

fs/bcachefs/btree_locking.c

@@ -431,7 +431,8 @@ void bch2_btree_node_lock_write_nofail(struct btree_trans *trans,
 
 static inline bool btree_path_get_locks(struct btree_trans *trans,
 					struct btree_path *path,
-					bool upgrade)
+					bool upgrade,
+					struct get_locks_fail *f)
 {
 	unsigned l = path->level;
 	int fail_idx = -1;
@@ -442,8 +443,14 @@ static inline bool btree_path_get_locks(struct btree_trans *trans,
 
 		if (!(upgrade
 		      ? bch2_btree_node_upgrade(trans, path, l)
-		      : bch2_btree_node_relock(trans, path, l)))
-			fail_idx = l;
+		      : bch2_btree_node_relock(trans, path, l))) {
+			fail_idx	= l;
+
+			if (f) {
+				f->l	= l;
+				f->b	= path->l[l].b;
+			}
+		}
 
 		l++;
 	} while (l < path->locks_want);
@@ -584,7 +591,9 @@ __flatten
 bool bch2_btree_path_relock_norestart(struct btree_trans *trans,
 			struct btree_path *path, unsigned long trace_ip)
 {
-	return btree_path_get_locks(trans, path, false);
+	struct get_locks_fail f;
+
+	return btree_path_get_locks(trans, path, false, &f);
 }
 
 int __bch2_btree_path_relock(struct btree_trans *trans,
@@ -600,22 +609,24 @@ int __bch2_btree_path_relock(struct btree_trans *trans,
 
 bool bch2_btree_path_upgrade_noupgrade_sibs(struct btree_trans *trans,
 			       struct btree_path *path,
-			       unsigned new_locks_want)
+			       unsigned new_locks_want,
+			       struct get_locks_fail *f)
 {
 	EBUG_ON(path->locks_want >= new_locks_want);
 
 	path->locks_want = new_locks_want;
 
-	return btree_path_get_locks(trans, path, true);
+	return btree_path_get_locks(trans, path, true, f);
 }
 
 bool __bch2_btree_path_upgrade(struct btree_trans *trans,
 			       struct btree_path *path,
-			       unsigned new_locks_want)
+			       unsigned new_locks_want,
+			       struct get_locks_fail *f)
 {
 	struct btree_path *linked;
 
-	if (bch2_btree_path_upgrade_noupgrade_sibs(trans, path, new_locks_want))
+	if (bch2_btree_path_upgrade_noupgrade_sibs(trans, path, new_locks_want, f))
 		return true;
 
 	/*
@@ -644,7 +655,7 @@ bool __bch2_btree_path_upgrade(struct btree_trans *trans,
 			    linked->btree_id == path->btree_id &&
 			    linked->locks_want < new_locks_want) {
 				linked->locks_want = new_locks_want;
-				btree_path_get_locks(trans, linked, true);
+				btree_path_get_locks(trans, linked, true, NULL);
 			}
 
 	return false;
@@ -656,6 +667,9 @@ void __bch2_btree_path_downgrade(struct btree_trans *trans,
 {
 	unsigned l;
 
+	if (trans->restarted)
+		return;
+
 	EBUG_ON(path->locks_want < new_locks_want);
 
 	path->locks_want = new_locks_want;
@@ -674,6 +688,9 @@ void __bch2_btree_path_downgrade(struct btree_trans *trans,
 	}
 
 	bch2_btree_path_verify_locks(path);
+
+	path->downgrade_seq++;
+	trace_path_downgrade(trans, _RET_IP_, path);
 }
 
 /* Btree transaction locking: */
@@ -682,6 +699,9 @@ void bch2_trans_downgrade(struct btree_trans *trans)
 {
 	struct btree_path *path;
 
+	if (trans->restarted)
+		return;
+
 	trans_for_each_path(trans, path)
 		bch2_btree_path_downgrade(trans, path);
 }

fs/bcachefs/btree_locking.h

@@ -355,26 +355,36 @@ static inline bool bch2_btree_node_relock_notrace(struct btree_trans *trans,
 
 /* upgrade */
 
+
+struct get_locks_fail {
+	unsigned	l;
+	struct btree	*b;
+};
+
 bool bch2_btree_path_upgrade_noupgrade_sibs(struct btree_trans *,
-			       struct btree_path *, unsigned);
+			       struct btree_path *, unsigned,
+			       struct get_locks_fail *);
+
 bool __bch2_btree_path_upgrade(struct btree_trans *,
-			       struct btree_path *, unsigned);
+			       struct btree_path *, unsigned,
+			       struct get_locks_fail *);
 
 static inline int bch2_btree_path_upgrade(struct btree_trans *trans,
 					  struct btree_path *path,
 					  unsigned new_locks_want)
 {
+	struct get_locks_fail f;
 	unsigned old_locks_want = path->locks_want;
 
 	new_locks_want = min(new_locks_want, BTREE_MAX_DEPTH);
 
 	if (path->locks_want < new_locks_want
-	    ? __bch2_btree_path_upgrade(trans, path, new_locks_want)
+	    ? __bch2_btree_path_upgrade(trans, path, new_locks_want, &f)
 	    : path->uptodate == BTREE_ITER_UPTODATE)
 		return 0;
 
 	trace_and_count(trans->c, trans_restart_upgrade, trans, _THIS_IP_, path,
-			old_locks_want, new_locks_want);
+			old_locks_want, new_locks_want, &f);
 	return btree_trans_restart(trans, BCH_ERR_transaction_restart_upgrade);
 }
 

fs/bcachefs/btree_trans_commit.c

@@ -861,12 +861,7 @@ static inline int do_bch2_trans_commit(struct btree_trans *trans, unsigned flags
 	 */
 	bch2_journal_res_put(&c->journal, &trans->journal_res);
 
-	if (unlikely(ret))
-		return ret;
-
-	bch2_trans_downgrade(trans);
-
-	return 0;
+	return ret;
 }
 
 static int journal_reclaim_wait_done(struct bch_fs *c)
@@ -1135,6 +1130,8 @@ int __bch2_trans_commit(struct btree_trans *trans, unsigned flags)
 	if (likely(!(flags & BTREE_INSERT_NOCHECK_RW)))
 		bch2_write_ref_put(c, BCH_WRITE_REF_trans);
 out_reset:
+	if (!ret)
+		bch2_trans_downgrade(trans);
 	bch2_trans_reset_updates(trans);
 
 	return ret;

fs/bcachefs/btree_types.h

@@ -228,6 +228,8 @@ struct btree_path {
 	u8			sorted_idx;
 	u8			ref;
 	u8			intent_ref;
+	u32			alloc_seq;
+	u32			downgrade_seq;
 
 	/* btree_iter_copy starts here: */
 	struct bpos		pos;

fs/bcachefs/btree_update_interior.c

@@ -1987,7 +1987,7 @@ int bch2_btree_node_rewrite(struct btree_trans *trans,
 out:
 	if (new_path)
 		bch2_path_put(trans, new_path, true);
-	bch2_btree_path_downgrade(trans, iter->path);
+	bch2_trans_downgrade(trans);
 	return ret;
 err:
 	bch2_btree_node_free_never_used(as, trans, n);

fs/bcachefs/data_update.c

@@ -162,11 +162,7 @@ static int __bch2_data_update_index_update(struct btree_trans *trans,
 			if (((1U << i) & m->data_opts.rewrite_ptrs) &&
 			    (ptr = bch2_extent_has_ptr(old, p, bkey_i_to_s(insert))) &&
 			    !ptr->cached) {
-				bch2_bkey_drop_ptr_noerror(bkey_i_to_s(insert), ptr);
-				/*
-				 * See comment below:
 				bch2_extent_ptr_set_cached(bkey_i_to_s(insert), ptr);
-				*/
 				rewrites_found |= 1U << i;
 			}
 			i++;
@@ -212,14 +208,8 @@ static int __bch2_data_update_index_update(struct btree_trans *trans,
 			if (!p.ptr.cached &&
 			    durability - ptr_durability >= m->op.opts.data_replicas) {
 				durability -= ptr_durability;
-				bch2_bkey_drop_ptr_noerror(bkey_i_to_s(insert), &entry->ptr);
-				/*
-				 * Currently, we're dropping unneeded replicas
-				 * instead of marking them as cached, since
-				 * cached data in stripe buckets prevents them
-				 * from being reused:
+
 				bch2_extent_ptr_set_cached(bkey_i_to_s(insert), &entry->ptr);
-				*/
 				goto restart_drop_extra_replicas;
 			}
 		}

fs/bcachefs/trace.h

@@ -1043,13 +1043,16 @@ DEFINE_EVENT(transaction_restart_iter,	trans_restart_btree_node_split,
 	TP_ARGS(trans, caller_ip, path)
 );
 
+struct get_locks_fail;
+
 TRACE_EVENT(trans_restart_upgrade,
 	TP_PROTO(struct btree_trans *trans,
 		 unsigned long caller_ip,
 		 struct btree_path *path,
 		 unsigned old_locks_want,
-		 unsigned new_locks_want),
-	TP_ARGS(trans, caller_ip, path, old_locks_want, new_locks_want),
+		 unsigned new_locks_want,
+		 struct get_locks_fail *f),
+	TP_ARGS(trans, caller_ip, path, old_locks_want, new_locks_want, f),
 
 	TP_STRUCT__entry(
 		__array(char,			trans_fn, 32	)
@@ -1057,6 +1060,11 @@ TRACE_EVENT(trans_restart_upgrade,
 		__field(u8,			btree_id	)
 		__field(u8,			old_locks_want	)
 		__field(u8,			new_locks_want	)
+		__field(u8,			level		)
+		__field(u32,			path_seq	)
+		__field(u32,			node_seq	)
+		__field(u32,			path_alloc_seq	)
+		__field(u32,			downgrade_seq)
 		TRACE_BPOS_entries(pos)
 	),
 
@@ -1066,10 +1074,15 @@ TRACE_EVENT(trans_restart_upgrade,
 		__entry->btree_id		= path->btree_id;
 		__entry->old_locks_want		= old_locks_want;
 		__entry->new_locks_want		= new_locks_want;
+		__entry->level			= f->l;
+		__entry->path_seq		= path->l[f->l].lock_seq;
+		__entry->node_seq		= IS_ERR_OR_NULL(f->b) ? 0 : f->b->c.lock.seq;
+		__entry->path_alloc_seq		= path->alloc_seq;
+		__entry->downgrade_seq		= path->downgrade_seq;
 		TRACE_BPOS_assign(pos, path->pos)
 	),
 
-	TP_printk("%s %pS btree %s pos %llu:%llu:%u locks_want %u -> %u",
+	TP_printk("%s %pS btree %s pos %llu:%llu:%u locks_want %u -> %u level %u path seq %u node seq %u alloc_seq %u downgrade_seq %u",
 		  __entry->trans_fn,
 		  (void *) __entry->caller_ip,
 		  bch2_btree_id_str(__entry->btree_id),
@@ -1077,7 +1090,12 @@ TRACE_EVENT(trans_restart_upgrade,
 		  __entry->pos_offset,
 		  __entry->pos_snapshot,
 		  __entry->old_locks_want,
-		  __entry->new_locks_want)
+		  __entry->new_locks_want,
+		  __entry->level,
+		  __entry->path_seq,
+		  __entry->node_seq,
+		  __entry->path_alloc_seq,
+		  __entry->downgrade_seq)
 );
 
 DEFINE_EVENT(transaction_restart_iter,	trans_restart_relock,
@@ -1238,6 +1256,27 @@ TRACE_EVENT(trans_restart_key_cache_key_realloced,
 		  __entry->new_u64s)
 );
 
+TRACE_EVENT(path_downgrade,
+	TP_PROTO(struct btree_trans *trans,
+		 unsigned long caller_ip,
+		 struct btree_path *path),
+	TP_ARGS(trans, caller_ip, path),
+
+	TP_STRUCT__entry(
+		__array(char,			trans_fn, 32	)
+		__field(unsigned long,		caller_ip	)
+	),
+
+	TP_fast_assign(
+		strscpy(__entry->trans_fn, trans->fn, sizeof(__entry->trans_fn));
+		__entry->caller_ip		= caller_ip;
+	),
+
+	TP_printk("%s %pS",
+		  __entry->trans_fn,
+		  (void *) __entry->caller_ip)
+);
+
 DEFINE_EVENT(transaction_event,	trans_restart_write_buffer_flush,
 	TP_PROTO(struct btree_trans *trans,
 		 unsigned long caller_ip),