bcachefs: New backtrace utility code

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

fs/bcachefs/btree_locking.c

@@ -191,7 +191,7 @@ 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_backtrace(&buf, trans->locking_wait.task);
+			bch2_prt_task_backtrace(&buf, trans->locking_wait.task);
 			printbuf_indent_sub(&buf, 2);
 			prt_newline(&buf);
 		}

fs/bcachefs/debug.c

@@ -527,7 +527,7 @@ 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_backtrace(&i->buf, trans->locking_wait.task);
+		bch2_prt_task_backtrace(&i->buf, trans->locking_wait.task);
 		printbuf_indent_sub(&i->buf, 2);
 		prt_newline(&i->buf);
 

fs/bcachefs/util.c

@@ -266,22 +266,48 @@ void bch2_print_string_as_lines(const char *prefix, const char *lines)
 	console_unlock();
 }
 
-int bch2_prt_backtrace(struct printbuf *out, struct task_struct *task)
+int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *task)
 {
-	unsigned long entries[32];
-	unsigned i, nr_entries;
+	unsigned nr_entries = 0;
+	int ret = 0;
+
+	stack->nr = 0;
+	ret = darray_make_room(stack, 32);
+	if (ret)
+		return ret;
 
 	if (!down_read_trylock(&task->signal->exec_update_lock))
-		return 0;
+		return -1;
+
+	do {
+		nr_entries = stack_trace_save_tsk(task, stack->data, stack->size, 0);
+	} while (nr_entries == stack->size &&
+		 !(ret = darray_make_room(stack, stack->size * 2)));
+
+	stack->nr = nr_entries;
+	up_read(&task->signal->exec_update_lock);
 
-	nr_entries = stack_trace_save_tsk(task, entries, ARRAY_SIZE(entries), 0);
-	for (i = 0; i < nr_entries; i++) {
-		prt_printf(out, "[<0>] %pB", (void *)entries[i]);
+	return ret;
+}
+
+void bch2_prt_backtrace(struct printbuf *out, bch_stacktrace *stack)
+{
+	unsigned long *i;
+
+	darray_for_each(*stack, i) {
+		prt_printf(out, "[<0>] %pB", (void *) *i);
 		prt_newline(out);
 	}
+}
 
-	up_read(&task->signal->exec_update_lock);
-	return 0;
+int bch2_prt_task_backtrace(struct printbuf *out, struct task_struct *task)
+{
+	bch_stacktrace stack = { 0 };
+	int ret = bch2_save_backtrace(&stack, task);
+
+	bch2_prt_backtrace(out, &stack);
+	darray_exit(&stack);
+	return ret;
 }
 
 /* time stats: */

fs/bcachefs/util.h

@@ -20,6 +20,8 @@
 
 #include "mean_and_variance.h"
 
+#include "darray.h"
+
 struct closure;
 
 #ifdef CONFIG_BCACHEFS_DEBUG
@@ -361,7 +363,11 @@ u64 bch2_read_flag_list(char *, const char * const[]);
 void bch2_prt_u64_binary(struct printbuf *, u64, unsigned);
 
 void bch2_print_string_as_lines(const char *prefix, const char *lines);
-int bch2_prt_backtrace(struct printbuf *, struct task_struct *);
+
+typedef DARRAY(unsigned long) bch_stacktrace;
+int bch2_save_backtrace(bch_stacktrace *stack, struct task_struct *);
+void bch2_prt_backtrace(struct printbuf *, bch_stacktrace *);
+int bch2_prt_task_backtrace(struct printbuf *, struct task_struct *);
 
 #define NR_QUANTILES	15
 #define QUANTILE_IDX(i)	inorder_to_eytzinger0(i, NR_QUANTILES)