Well, it looks like we really screwed up on this one. lttng-tools commit 02b3d1769d5f8a33e4109b1e681141c9295dfda6 introduced an important regression for lttng-ust tracing in the consumer daemon: after reading a sub-buffer, a check has been added to see whether there are more sub-buffers available to read, and if it is the case, it ensures the wakeup pipe will be awakened again.
The issue lies in the use of ustctl_put_next_subbuf() in this check. This acts as if the sub-buffer has been read, when in reality it has not been read. It therefore trashes the data contained by this sub-buffer. This check should use ustctl_put_subbuf(), which does not move the consumer position. This is a severe bug, and the fix needs to be applied to stable-2.6, stable-2.5, and stable-2.4. Fixes #861 Signed-off-by: Mathieu Desnoyers <[email protected]> --- src/common/ust-consumer/ust-consumer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/common/ust-consumer/ust-consumer.c b/src/common/ust-consumer/ust-consumer.c index 52b6979..24ba387 100644 --- a/src/common/ust-consumer/ust-consumer.c +++ b/src/common/ust-consumer/ust-consumer.c @@ -1882,7 +1882,7 @@ static int notify_if_more_data(struct lttng_consumer_stream *stream, goto end; } - ret = ustctl_put_next_subbuf(ustream); + ret = ustctl_put_subbuf(ustream); assert(!ret); /* This stream still has data. Flag it and wake up the data thread. */ -- 2.1.1 _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
