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Lock entity QoS while accessing it

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A QoS change can happen at the same time that a new reader for a
built-in topic is provisioned with historical data, and so cause reading
in inconsistent QoS, use-after-free or other fun things.

During QoS matching it is also necessary to guarantee the QoS doesn't
change (QoS changes affecting matching will be supported at some point,
and manipulating complex data structures where bitmasks determine which
parts are defined while reading the same data concurrently is a recipe
for disaster.

Signed-off-by: Erik Boasson <eb@ilities.com>
This commit is contained in:
Erik Boasson 2019-07-18 19:13:52 +02:00 • committed by eboasson
parent 103210bf8e
commit 09e08f7778
3 changed files with 34 additions and 4 deletions
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4
src/core/ddsc/src/dds_serdata_builtintopic.c
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@ -131,11 +131,12 @@ static struct ddsi_serdata *ddsi_serdata_builtin_from_keyhash (const struct ddsi
/* FIXME: not quite elegant to manage the creation of a serdata for a built-in topic via this function, but I also find it quite unelegant to let from_sample read straight from the underlying internal entity, and to_sample convert to the external format ... I could claim the internal entity is the "serialised form", but that forces wrapping it in a fragchain in one way or another, which, though possible, is also a bit lacking in elegance. */
const struct ddsi_sertopic_builtintopic *tp = (const struct ddsi_sertopic_builtintopic *)tpcmn;
/* keyhash must in host format (which the GUIDs always are internally) */
const struct entity_common *entity = ephash_lookup_guid_untyped (tp->gv->guid_hash, (const nn_guid_t *) keyhash->value);
struct entity_common *entity = ephash_lookup_guid_untyped (tp->gv->guid_hash, (const nn_guid_t *) keyhash->value);
struct ddsi_serdata_builtintopic *d = serdata_builtin_new(tp, entity ? SDK_DATA : SDK_KEY);
memcpy (&d->key, keyhash->value, sizeof (d->key));
if (entity)
{
ddsrt_mutex_lock (&entity->qos_lock);
switch (entity->kind)
{
case EK_PARTICIPANT:
@ -163,6 +164,7 @@ static struct ddsi_serdata *ddsi_serdata_builtin_from_keyhash (const struct ddsi
from_entity_pwr (d, (const struct proxy_writer *) entity);
break;
}
ddsrt_mutex_unlock (&entity->qos_lock);
}
return fix_serdata_builtin(d, tp->c.serdata_basehash);
}