From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 12 Jan 2015 18:27:53 +0000 (-0500)
Subject: Fix: add urcu-bp TLS fixup
X-Git-Tag: v2.7.0-rc1~64
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=1556a5495c92bdd99e57faa87e21eb0b6f95c3a2;p=lttng-ust.git

Fix: add urcu-bp TLS fixup

When performing a library base address statedump, the UST threads can
grab the RCU read-side lock, which touch a TLS. We should "pre-fault"
this TLS in the constructor to eliminate a deadlock involving libc
dynamic loader lock.

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 3df2adc6..378ca21c 100644
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -335,6 +335,16 @@ void lttng_fixup_ust_mutex_nest_tls(void)
 	asm volatile ("" : : "m" (URCU_TLS(ust_mutex_nest)));
 }
 
+/*
+ * Fixup urcu bp TLS.
+ */
+static
+void lttng_fixup_urcu_bp_tls(void)
+{
+	rcu_read_lock();
+	rcu_read_unlock();
+}
+
 int lttng_get_notify_socket(void *owner)
 {
 	struct sock_info *info = owner;
@@ -1419,6 +1429,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
 	 * to be the dynamic linker mutex) and ust_lock, taken within
 	 * the ust lock.
 	 */
+	lttng_fixup_urcu_bp_tls();
 	lttng_fixup_ringbuffer_tls();
 	lttng_fixup_vtid_tls();
 	lttng_fixup_nest_count_tls();