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SubjectRe: [PATCH 2/2] tracepoint: introduce *_noupdate APIs.
* Lai Jiangshan (laijs@cn.fujitsu.com) wrote:
>
> new APIs separate tracepoint_probe_register(),
> tracepoint_probe_unregister() into 2 steps. The first step of them
> is just update tracepoint_entry, not connect or disconnect.
>
> this patch introduce tracepoint_probe_update_all() for update all.
>
> these APIs are very useful for registering a lots of probes
> but just update once only. and a very important thing is that
> *_noupdate APIs do not require module_mutex.
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>

[...]

> +/**
> + * tracepoint_probe_update_all - update tracepoints
> + */
> +void tracepoint_probe_update_all(void)
> +{
> + LIST_HEAD(release_probes);
> + struct tp_probes *pos, *next;
> +
> + mutex_lock(&tracepoints_mutex);
> + if (!need_update) {
> + mutex_unlock(&tracepoints_mutex);
> + return;
> + }
> + if (!list_empty(&old_probes))
> + list_replace_init(&old_probes, &release_probes);
> + need_update = 0;
> + mutex_unlock(&tracepoints_mutex);
> +
> + tracepoint_update_probes();

I think the read-side of this release_probes list should be protected by
the tracepoints_mutex too. Two concurrent tracepoint_probe_update_all()
could cause havoc here :


mutex_lock(&tracepoints_mutex);

> + list_for_each_entry_safe(pos, next, &release_probes, u.list) {
> + list_del(&pos->u.list);
> + call_rcu_sched(&pos->u.rcu, rcu_free_old_probes);
> + }

mutex_unlock(&tracepoints_mutex);

?

The rest looks good.

Mathieu

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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