From: Julien Desfossez <jdesfossez@efficios.com>
Date: Thu, 23 Nov 2017 23:43:52 +0000 (-0500)
Subject: Fix: prevent calling adding the same trace recursively
X-Git-Tag: v1.4.4~3
X-Git-Url: http://git.efficios.com/?p=babeltrace.git;a=commitdiff_plain;h=1e8e8e2fb8ef9e36cbc2c5a692e9fa1d11cbb52a

Fix: prevent calling adding the same trace recursively

add_one_trace may need to fetch new streams, which may lead to adding
new traces to the ctf_traces hashtable and recursively calling
add_one_trace. This is problematic because we cannot modify a hashtable
we are iterating on, and we cannot perform twice the add_one_trace for
the same trace.

This fix, ensures this situation cannot happen, by checking if the
number of traces changed during the iteration and by making sure a trace
is considered in_use as soon as we enter the add_one_trace function.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Acked-by: Jonathan Rajotte-Julien <jonathan.rajotte-julien@efficios.com>
Tested-by: Jonathan Rajotte-Julien <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/formats/lttng-live/lttng-live-comm.c b/formats/lttng-live/lttng-live-comm.c
index b61371fc..e0892638 100644
--- a/formats/lttng-live/lttng-live-comm.c
+++ b/formats/lttng-live/lttng-live-comm.c
@@ -1499,6 +1499,12 @@ int add_one_trace(struct lttng_live_ctx *ctx,
 		ret = 0;
 		goto end;
 	}
+	/*
+	 * add_one_trace can be called recursively if during the
+	 * bt_context_add_trace call we need to fetch new streams, so we need to
+	 * prevent a recursive call to process our current trace.
+	 */
+	trace->in_use = 1;
 
 	BT_INIT_LIST_HEAD(&mmap_list.head);
 
@@ -1561,7 +1567,6 @@ int add_one_trace(struct lttng_live_ctx *ctx,
 	}
 
 	trace->trace_id = ret;
-	trace->in_use = 1;
 	printf_verbose("Trace now in use, id = %d\n", trace->trace_id);
 
 	goto end;
@@ -1630,9 +1635,13 @@ int add_traces(struct lttng_live_ctx *ctx)
 	GHashTableIter it;
 	gpointer key;
 	gpointer value;
+	unsigned int nr_traces;
 
 	printf_verbose("Begin add traces\n");
 
+retry:
+	nr_traces = g_hash_table_size(ctx->session->ctf_traces);
+
 	ret = check_traces_metadata(ctx);
 	if (ret < 0) {
 		goto end;
@@ -1645,6 +1654,15 @@ int add_traces(struct lttng_live_ctx *ctx)
 		if (ret < 0) {
 			goto end;
 		}
+		/*
+		 * If a new trace got added while we were adding the trace, the
+		 * iterator is invalid and we have to restart.
+		 */
+		if (g_hash_table_size(ctx->session->ctf_traces) != nr_traces) {
+			printf_verbose("New trace(s) added during add_one_trace()\n");
+			printf_verbose("JORAJ: GREP HERE\n");
+			goto retry;
+		}
 	}
 
 	ret = 0;