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bcachefs: Fix btree_trans list ordering

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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>
This commit is contained in:
Kent Overstreet 2024-06-22 22:11:01 -04:00
parent de611ab6fc
commit 1aaf5cb41b
2 changed files with 34 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
fs/bcachefs/btree_iter.c
View File

@ -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;

36
fs/bcachefs/debug.c
View File

@ -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);