Re: [PATCHv3 1/7] uprobe: Add support for session consumer

On 09/13, Jiri Olsa wrote:

I'm not sure the realloc will help, I feel like we need to allocate return
consumer for each called handler separately to be safe

How about something like the (pseudo) code below? Note that this way
we do not need uprobe->consumers_cnt. Note also that krealloc() should
be unlikely and it checks ksize() before it does another allocation.

Oleg.

static size_t ri_size(int consumers_cnt)
{
	return sizeof(struct return_instance) +
		      sizeof(struct return_consumer) * consumers_cnt;
}

#define DEF_CNT	4	// arbitrary value

static struct return_instance *alloc_return_instance(void)
{
	struct return_instance *ri;

	ri = kzalloc(ri_size(DEF_CNT), GFP_KERNEL);
	if (!ri)
		return ZERO_SIZE_PTR;

	ri->consumers_cnt = DEF_CNT;
	return ri;
}

static struct return_instance *push_id_cookie(struct return_instance *ri, int idx,
						__u64 id, __u64 cookie)
{
	if (unlikely(ri == ZERO_SIZE_PTR))
		return ri;

	if (unlikely(idx >= ri->consumers_cnt)) {
		ri->consumers_cnt += DEF_CNT;
		ri = krealloc(ri, ri_size(ri->consumers_cnt), GFP_KERNEL);
		if (!ri) {
			kfree(ri);
			return ZERO_SIZE_PTR;
		}
	}

	ri->consumers[idx].id = id;
	ri->consumers[idx].cookie = cookie;
	return ri;
}

static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
{
	...
	struct return_instance *ri = NULL;
	int push_idx = 0;

	list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
		__u64 cookie = 0;
		int rc = 0;

		if (uc->handler)
			rc = uc->handler(uc, regs, &cookie);

		remove &= rc;
		has_consumers = true;

		if (!uc->ret_handler || rc == UPROBE_HANDLER_REMOVE || rc == 2)
			continue;

		if (!ri)
			ri = alloc_return_instance();

		// or, better if (rc = UPROBE_HANDLER_I_WANT_MY_COOKIE)
		if (uc->handler))
			ri = push_id_cookie(ri, push_idx++, uc->id, cookie);
	}

	if (!ZERO_OR_NULL_PTR(ri)) {
		ri->consumers_cnt = push_idx;
		prepare_uretprobe(uprobe, regs, ri);
	}

	...
}