From 1aaf5cb41b8e92dcd3ac7e047124cb0e3e27f1c1 Mon Sep 17 00:00:00 2001
From: Kent Overstreet <kent.overstreet@linux.dev>
Date: Sat, 22 Jun 2024 22:11:01 -0400
Subject: [PATCH] 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: Kent Overstreet <kent.overstreet@linux.dev>
---
fs/bcachefs/btree_iter.c | 9 ++-------
fs/bcachefs/debug.c | 36 ++++++++++++++++++++++++++++++++----
2 files changed, 34 insertions(+), 11 deletions(-)
diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
index 15c1c7cfefe6..0ed9e6574fcd 100644
--- a/fs/bcachefs/btree_iter.c
+++ b/fs/bcachefs/btree_iter.c
@@ -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;
diff --git a/fs/bcachefs/debug.c b/fs/bcachefs/debug.c
index 61c50522abb9..f0d4727c4dc2 100644
--- a/fs/bcachefs/debug.c
+++ b/fs/bcachefs/debug.c
@@ -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 @@ restart:
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);