bcachefs: Improve would_deadlock trace event

We now include backtraces for every thread involved in the cycle.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_locking.c

@@ -86,8 +86,14 @@ static noinline void print_cycle(struct printbuf *out, struct lock_graph *g)
 	prt_printf(out, "Found lock cycle (%u entries):", g->nr);
 	prt_newline(out);
 
-	for (i = g->g; i < g->g + g->nr; i++)
+	for (i = g->g; i < g->g + g->nr; i++) {
+		struct task_struct *task = READ_ONCE(i->trans->locking_wait.task);
+		if (!task)
+			continue;
+
 		bch2_btree_trans_to_text(out, i->trans);
+		bch2_prt_task_backtrace(out, task, i == g->g ? 5 : 1);
+	}
 }
 
 static noinline void print_chain(struct printbuf *out, struct lock_graph *g)
@@ -144,8 +150,7 @@ static bool lock_graph_remove_non_waiters(struct lock_graph *g)
 	return false;
 }
 
-static void trace_would_deadlock(struct lock_graph *g, struct btree_trans *trans,
-				 unsigned long ip)
+static void trace_would_deadlock(struct lock_graph *g, struct btree_trans *trans)
 {
 	struct bch_fs *c = trans->c;
 
@@ -157,7 +162,7 @@ static void trace_would_deadlock(struct lock_graph *g, struct btree_trans *trans
 		buf.atomic++;
 		print_cycle(&buf, g);
 
-		trace_trans_restart_would_deadlock(trans, ip, buf.buf);
+		trace_trans_restart_would_deadlock(trans, buf.buf);
 		printbuf_exit(&buf);
 	}
 }
@@ -165,7 +170,7 @@ static void trace_would_deadlock(struct lock_graph *g, struct btree_trans *trans
 static int abort_lock(struct lock_graph *g, struct trans_waiting_for_lock *i)
 {
 	if (i == g->g) {
-		trace_would_deadlock(g, i->trans, _RET_IP_);
+		trace_would_deadlock(g, i->trans);
 		return btree_trans_restart(i->trans, BCH_ERR_transaction_restart_would_deadlock);
 	} else {
 		i->trans->lock_must_abort = true;
@@ -222,7 +227,7 @@ static noinline int break_cycle(struct lock_graph *g, struct printbuf *cycle)
 			prt_printf(&buf, "backtrace:");
 			prt_newline(&buf);
 			printbuf_indent_add(&buf, 2);
-			bch2_prt_task_backtrace(&buf, trans->locking_wait.task);
+			bch2_prt_task_backtrace(&buf, trans->locking_wait.task, 2);
 			printbuf_indent_sub(&buf, 2);
 			prt_newline(&buf);
 		}
@@ -291,7 +296,7 @@ int bch2_check_for_deadlock(struct btree_trans *trans, struct printbuf *cycle)
 		if (cycle)
 			return -1;
 
-		trace_would_deadlock(&g, trans, _RET_IP_);
+		trace_would_deadlock(&g, trans);
 		return btree_trans_restart(trans, BCH_ERR_transaction_restart_would_deadlock);
 	}
 

fs/bcachefs/debug.c

@@ -627,7 +627,7 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf,
 		prt_printf(&i->buf, "backtrace:");
 		prt_newline(&i->buf);
 		printbuf_indent_add(&i->buf, 2);
-		bch2_prt_task_backtrace(&i->buf, task);
+		bch2_prt_task_backtrace(&i->buf, task, 0);
 		printbuf_indent_sub(&i->buf, 2);
 		prt_newline(&i->buf);
 

fs/bcachefs/trace.h

@@ -72,6 +72,27 @@ DECLARE_EVENT_CLASS(trans_str,
 		  __entry->trans_fn, (void *) __entry->caller_ip, __get_str(str))
 );
 
+DECLARE_EVENT_CLASS(trans_str_nocaller,
+	TP_PROTO(struct btree_trans *trans, const char *str),
+	TP_ARGS(trans, str),
+
+	TP_STRUCT__entry(
+		__field(dev_t,		dev			)
+		__array(char,		trans_fn, 32		)
+		__string(str,		str			)
+	),
+
+	TP_fast_assign(
+		__entry->dev		= trans->c->dev;
+		strscpy(__entry->trans_fn, trans->fn, sizeof(__entry->trans_fn));
+		__assign_str(str, str);
+	),
+
+	TP_printk("%d,%d %s %s",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->trans_fn, __get_str(str))
+);
+
 DECLARE_EVENT_CLASS(btree_node_nofs,
 	TP_PROTO(struct bch_fs *c, struct btree *b),
 	TP_ARGS(c, b),
@@ -1243,11 +1264,10 @@ DEFINE_EVENT(transaction_restart_iter,	trans_restart_memory_allocation_failure,
 	TP_ARGS(trans, caller_ip, path)
 );
 
-DEFINE_EVENT(trans_str, trans_restart_would_deadlock,
+DEFINE_EVENT(trans_str_nocaller, trans_restart_would_deadlock,
 	TP_PROTO(struct btree_trans *trans,
-		 unsigned long caller_ip,
 		 const char *cycle),
-	TP_ARGS(trans, caller_ip, cycle)
+	TP_ARGS(trans, cycle)
 );
 
 DEFINE_EVENT(transaction_event,	trans_restart_would_deadlock_recursion_limit,

fs/bcachefs/util.c

@@ -267,7 +267,7 @@ void bch2_print_string_as_lines(const char *prefix, const char *lines)
 	console_unlock();
 }
 
-int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *task)
+int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *task, unsigned skipnr)
 {
 #ifdef CONFIG_STACKTRACE
 	unsigned nr_entries = 0;
@@ -282,7 +282,7 @@ int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *task)
 		return -1;
 
 	do {
-		nr_entries = stack_trace_save_tsk(task, stack->data, stack->size, 0);
+		nr_entries = stack_trace_save_tsk(task, stack->data, stack->size, skipnr + 1);
 	} while (nr_entries == stack->size &&
 		 !(ret = darray_make_room(stack, stack->size * 2)));
 
@@ -303,10 +303,10 @@ void bch2_prt_backtrace(struct printbuf *out, bch_stacktrace *stack)
 	}
 }
 
-int bch2_prt_task_backtrace(struct printbuf *out, struct task_struct *task)
+int bch2_prt_task_backtrace(struct printbuf *out, struct task_struct *task, unsigned skipnr)
 {
 	bch_stacktrace stack = { 0 };
-	int ret = bch2_save_backtrace(&stack, task);
+	int ret = bch2_save_backtrace(&stack, task, skipnr + 1);
 
 	bch2_prt_backtrace(out, &stack);
 	darray_exit(&stack);

fs/bcachefs/util.h

@@ -347,9 +347,9 @@ void bch2_prt_u64_binary(struct printbuf *, u64, unsigned);
 void bch2_print_string_as_lines(const char *prefix, const char *lines);
 
 typedef DARRAY(unsigned long) bch_stacktrace;
-int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *);
+int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *, unsigned);
 void bch2_prt_backtrace(struct printbuf *, bch_stacktrace *);
-int bch2_prt_task_backtrace(struct printbuf *, struct task_struct *);
+int bch2_prt_task_backtrace(struct printbuf *, struct task_struct *, unsigned);
 
 #define NR_QUANTILES	15
 #define QUANTILE_IDX(i)	inorder_to_eytzinger0(i, NR_QUANTILES)