Re: [RFC PATCH] Kernel Tracepoints (update)

[Masami Hiramatsu <mhiramat@redhat.com>]

Hi Mathieu,

I found a bug.
Mathieu Desnoyers wrote:
[...]

> +/*
> + * Remove the tracepoint from the tracepoint hash table. Must be called with
> + * mutex_lock held.
> + */
> +static int remove_tracepoint(const char *name)
> +{
> +	struct hlist_head *head;
> +	struct hlist_node *node;
> +	struct tracepoint_entry *e;
> +	int found = 0;
> +	size_t len = strlen(name) + 1;
> +	u32 hash = jhash(name, len-1, 0);
> +
> +	head = &tracepoint_table[hash & ((1 << TRACEPOINT_HASH_BITS)-1)];
> +	hlist_for_each_entry(e, node, head, hlist) {
> +		if (!strcmp(name, e->name)) {
> +			found = 1;
> +			break;
> +		}
> +	}
> +	if (!found)
> +		return -ENOENT;

before removing, you have to ensure refcount == 0. So,
	if (e->refcount != 0)
		return -EBUSY;

> +	hlist_del(&e->hlist);
> +	/* Make sure the call_rcu has been executed */
> +	if (e->rcu_pending)
> +		rcu_barrier();
> +	kfree(e);
> +	return 0;
> +}

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com