Commit 1aaf5cb4 authored by Kent Overstreet's avatar Kent Overstreet
Browse files

bcachefs: Fix btree_trans list ordering 



The debug code relies on btree_trans_list being ordered so that it can
resume on subsequent calls or lock restarts.

However, it was using trans->locknig_wait.task.pid, which is incorrect
since btree_trans objects are cached and reused - typically by different
tasks.

Fix this by switching to pointer order, and also sort them lazily when
required - speeding up the btree_trans_get() fastpath.

Signed-off-by: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent de611ab6

fs/bcachefs/btree_iter.c

+2 −7
Original line number Diff line number Diff line
@@ -3149,15 +3149,10 @@ struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx) 
			BUG_ON(pos_task &&

			       pid == pos_task->pid &&

			       pos->locked);



			if (pos_task && pid < pos_task->pid) {

				list_add_tail(&trans->list, &pos->list);

				goto list_add_done;

			}

		}

	}

	list_add_tail(&trans->list, &c->btree_trans_list);

list_add_done:



	list_add(&trans->list, &c->btree_trans_list);

	seqmutex_unlock(&c->btree_trans_lock);

got_trans:

	trans->c		= c;

fs/bcachefs/debug.c

+32 −4
Original line number Diff line number Diff line
@@ -568,6 +568,32 @@ static const struct file_operations cached_btree_nodes_ops = { 
	.read		= bch2_cached_btree_nodes_read,

};



typedef int (*list_cmp_fn)(const struct list_head *l, const struct list_head *r);



static void list_sort(struct list_head *head, list_cmp_fn cmp)

{

	struct list_head *pos;



	list_for_each(pos, head)

		while (!list_is_last(pos, head) &&

		       cmp(pos, pos->next) > 0) {

			struct list_head *pos2, *next = pos->next;



			list_del(next);

			list_for_each(pos2, head)

				if (cmp(next, pos2) < 0)

					goto pos_found;

			BUG();

pos_found:

			list_add_tail(next, pos2);

		}

}



static int list_ptr_order_cmp(const struct list_head *l, const struct list_head *r)

{

	return cmp_int(l, r);

}



static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf,

					    size_t size, loff_t *ppos)

{
@@ -581,12 +607,14 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf, 
	i->ret	= 0;

restart:

	seqmutex_lock(&c->btree_trans_lock);

	list_for_each_entry(trans, &c->btree_trans_list, list) {

		struct task_struct *task = READ_ONCE(trans->locking_wait.task);

	list_sort(&c->btree_trans_list, list_ptr_order_cmp);



		if (!task || task->pid <= i->iter)

	list_for_each_entry(trans, &c->btree_trans_list, list) {

		if ((ulong) trans < i->iter)

			continue;



		i->iter = (ulong) trans;



		if (!closure_get_not_zero(&trans->ref))

			continue;
@@ -596,7 +624,7 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf, 


		prt_printf(&i->buf, "backtrace:\n");

		printbuf_indent_add(&i->buf, 2);

		bch2_prt_task_backtrace(&i->buf, task, 0, GFP_KERNEL);

		bch2_prt_task_backtrace(&i->buf, trans->locking_wait.task, 0, GFP_KERNEL);

		printbuf_indent_sub(&i->buf, 2);

		prt_newline(&i->buf);