The locking order comment in consumer.h is incorrect. First, its
description of locking order is not in sync with the comment found in
consumer-metadata-cache.h. The comment in struct consumer_metadata_cache
only states that the metadata cache lock nests inside the consumer_data
lock, and does not mention the stream lock, which implies that the
metadata cache lock does NOT nest inside the stream lock. But let's
investigate further to confirm:
* lttng_consumer_read_subbuffer() acquires the stream lock, and then
calls lttng_ustconsumer_read_subbuffer() with stream lock held,
and then invokes commin_one_metadata_packet(), which acquires the
metadata cache lock.
* lttng_ustconsumer_sync_metadata() acquires the metadata stream lock,
and calls commit_one_metadata_packet(), which takes the metadata cache
lock.
Therefore, update the comment in consumer.h to state that the metadata
cache lock nests INSIDE the stream lock, and update
consumer_del_metadata_stream() accordingly.
This should take care of fixing the locking order reversal found by
Coverity.
CID
1368314 (#1 of 1): Thread deadlock (ORDER_REVERSAL)
CID
1368319: Program hangs (ORDER_REVERSAL)
Fixes: 5feafd4130 "Fix: protect the channel's metadata stream using the metadata cache lock"
Fixes: 1ea6cc572b "Fix: lock nesting order reversed"
Fixes: fb549e7ac2 "Fix: reverse channel and metadata cache lock nesting order"
Reported-by: Coverity Scan
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>