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uorb: fix several race conditions during topic initialization

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Possible race conditions (they all happen between the check of existence
of a topic and trying to create the node):
- single instance, with multiple advertisers during the first advertise:
  both advertisers see the topic as non-existent and try to advertise it.
  One of them will fail, leading to an error message.
  This is the cause for telemetry_status advert failure seen in SITL in
  rare cases.
- multi-instance: subscription to non-existing instance -> px4_open fails,
  and the subscriber tries to create the node. If during that time a
  publisher publishes that instance, the subscriber will get (instance+1)
  (or fails if the max number of instances is exceeded).
  This is a race that goes pretty much unnoticed.
- multi-instance: 2 publishers can get the same instance (if is_published()
  is false in case both have not published data yet).
  This can also go unnoticed.
  Therefore the patch changes where _advertised is set: it is now set
  directly during the advertisement instead of during publication.
This commit is contained in:
Beat Küng
2019-11-21 07:57:39 +01:00
committed by Daniel Agar
parent 63b2befeed
commit 6c8048d057
6 changed files with 41 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
src/modules/uORB/uORBManager.cpp
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@@ -327,14 +327,12 @@ int uORB::Manager::orb_get_interval(int handle, unsigned *interval)
return ret;
}
int uORB::Manager::node_advertise(const struct orb_metadata *meta, int *instance, int priority)
int uORB::Manager::node_advertise(const struct orb_metadata *meta, bool is_advertiser, int *instance, int priority)
{
int ret = PX4_ERROR;
/* fill advertiser data */
if (get_device_master()) {
ret = _device_master->advertise(meta, instance, priority);
ret = _device_master->advertise(meta, is_advertiser, instance, priority);
}
/* it's PX4_OK if it already exists */
@@ -384,7 +382,7 @@ int uORB::Manager::node_open(const struct orb_metadata *meta, bool advertiser, i
if (fd < 0) {
/* try to create the node */
ret = node_advertise(meta, instance, priority);
ret = node_advertise(meta, advertiser, instance, priority);
if (ret == PX4_OK) {
/* update the path, as it might have been updated during the node_advertise call */
@@ -396,7 +394,7 @@ int uORB::Manager::node_open(const struct orb_metadata *meta, bool advertiser, i
}
}
/* on success, try the open again */
/* on success, try to open again */
if (ret == PX4_OK) {
fd = px4_open(path, (advertiser) ? PX4_F_WRONLY : PX4_F_RDONLY);
}