From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 13 Jun 2012 08:46:44 +0000 (-0400)
Subject: Fix: perform TLS fixup of nest count outside of UST mutex
X-Git-Tag: v2.0.4~1
X-Git-Url: http://git.lttng.org/?p=lttng-ust.git;a=commitdiff_plain;h=e38c8fc1be27964f9a87afca4db5ae164fe09371;hp=3b8b68e73ec9b2b3cf550048046d3f7f69050688

Fix: perform TLS fixup of nest count outside of UST mutex

Could otherwise lead to a deadlock between the dynamic linker, TLS
fixup, and the UST mutex due to reversed lock acquisition order.

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

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index 8c864f8c..2c787f75 100644
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -136,6 +136,15 @@ extern void ltt_ring_buffer_client_overwrite_exit(void);
 extern void ltt_ring_buffer_client_discard_exit(void);
 extern void ltt_ring_buffer_metadata_client_exit(void);
 
+/*
+ * Force a read (imply TLS fixup for dlopen) of TLS variables.
+ */
+static
+void lttng_fixup_nest_count_tls(void)
+{
+	asm volatile ("" : : "m" (lttng_ust_nest_count));
+}
+
 static
 int setup_local_apps(void)
 {
@@ -860,6 +869,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
 	lttng_fixup_event_tls();
 	lttng_fixup_ringbuffer_tls();
 	lttng_fixup_vtid_tls();
+	lttng_fixup_nest_count_tls();
 
 	/*
 	 * We want precise control over the order in which we construct