From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 18 Aug 2016 20:07:30 +0000 (-0400)
Subject: Fix: perf counter context deadlock
X-Git-Tag: v2.7.5~9
X-Git-Url: http://git.liburcu.org/?p=lttng-ust.git;a=commitdiff_plain;h=3ffb9d255cb5277f0cdfc464410dbce46eeec9dd

Fix: perf counter context deadlock

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/liblttng-ust/lttng-ust-statedump.c b/liblttng-ust/lttng-ust-statedump.c
index 37f067ff..4f989bca 100644
--- a/liblttng-ust/lttng-ust-statedump.c
+++ b/liblttng-ust/lttng-ust-statedump.c
@@ -237,12 +237,22 @@ int do_baddr_statedump(void *owner)
  * session, statedumps from different processes may be
  * interleaved. The vpid context should be used to identify which
  * events belong to which process.
+ *
+ * Grab the ust_lock outside of the RCU read-side lock because we
+ * perform synchronize_rcu with the ust_lock held, which can trigger
+ * deadlocks otherwise.
  */
 int do_lttng_ust_statedump(void *owner)
 {
+	ust_lock_nocheck();
 	trace_statedump_start(owner);
+	ust_unlock();
+
 	do_baddr_statedump(owner);
+
+	ust_lock_nocheck();
 	trace_statedump_end(owner);
+	ust_unlock();
 
 	return 0;
 }