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rtpmanager/rtsession: data race leading to critical warnings

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This is a fix for a data race leading to:

> GLib-CRITICAL: g_hash_table_foreach:
>   assertion 'version == hash_table->version' failed

Identified sequence:

* `rtp_session_on_timeout` acquires the lock on `session` and proceeds with its
  processing.
* `rtp_session_process_rtcp` is called (debug log : received RTCP packet) and
  attempts to acquire the lock on `session`, which is still held by
  `rtp_session_on_timeout`.
* as part of an hash table iterator, `rtp_session_on_timeout` transitively
  invokes `source_caps` which releases the lock on `session` so as to call
  `session->callbacks.caps`.
* Since `rtp_session_process_rtcp` was waiting for the lock to be released, it
  succeeds in acquiring it and proceeds with `rtp_session_process_rr` which
  transitively calls `g_hash_table_insert` via `add_source`.
* After `source_caps` re-acquires the lock and gives the control flow back to
  `rtp_session_on_timeout`, the hash table iterator is changed, resulting in the
  assertion failure.

This commits copies `sess->ssrcs[sess->mask_idx]` and iterates on the copy so
the iterator is not affected by a concurrent change due to the lock being
released in the `source_caps` callback.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4585>
This commit is contained in:
François Laignel 2023-05-09 17:28:49 +02:00 committed by GStreamer Marge Bot
parent 9f8d69540c
commit b9f7ab6052
1 changed files with 14 additions and 7 deletions
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21
subprojects/gst-plugins-good/gst/rtpmanager/rtpsession.c
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@ -4712,20 +4712,27 @@ rtp_session_on_timeout (RTPSession * sess, GstClockTime current_time,
/* check if all the buffers are empty after generation */
all_empty = TRUE;
/* Make a local copy of the hashtable. We need to do this because the
* generate_rtcp stage below releases the session lock. */
table_copy = g_hash_table_new_full (NULL, NULL, NULL,
(GDestroyNotify) g_object_unref);
g_hash_table_foreach (sess->ssrcs[sess->mask_idx],
(GHFunc) clone_ssrcs_hashtable, table_copy);
GST_DEBUG
("doing RTCP generation %u for %u sources, early %d, may suppress %d",
sess->generation, data.num_to_report, data.is_early, data.may_suppress);
/* generate RTCP for all internal sources */
g_hash_table_foreach (sess->ssrcs[sess->mask_idx],
(GHFunc) generate_rtcp, &data);
/* generate RTCP for all internal sources, this might release the
* session lock. */
g_hash_table_foreach (table_copy, (GHFunc) generate_rtcp, &data);
g_hash_table_foreach (sess->ssrcs[sess->mask_idx],
(GHFunc) generate_twcc, &data);
g_hash_table_foreach (table_copy, (GHFunc) generate_twcc, &data);
/* update the generation for all the sources that have been reported */
g_hash_table_foreach (sess->ssrcs[sess->mask_idx],
(GHFunc) update_generation, &data);
g_hash_table_foreach (table_copy, (GHFunc) update_generation, &data);
g_hash_table_destroy (table_copy);
/* we keep track of the last report time in order to timeout inactive
* receivers or senders */