From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 28 Sep 2011 00:39:07 +0000 (-0400)
Subject: Reset vtid after fork in child
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=a93bfc45c7cc2117d27f69eb420ab3333280e026;p=ust.git

Reset vtid after fork in child

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

diff --git a/include/ust/lttng-events.h b/include/ust/lttng-events.h
index 7a8cf6f..6bb4e8c 100644
--- a/include/ust/lttng-events.h
+++ b/include/ust/lttng-events.h
@@ -322,5 +322,6 @@ void lttng_remove_context_field(struct lttng_ctx **ctx_p,
 void lttng_destroy_context(struct lttng_ctx *ctx);
 int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx);
 int lttng_add_pthread_id_to_ctx(struct lttng_ctx **ctx);
+void lttng_context_vtid_reset(void);
 
 #endif /* _UST_LTTNG_EVENTS_H */
diff --git a/libust/lttng-context-vtid.c b/libust/lttng-context-vtid.c
index fd1e320..a7e1c81 100644
--- a/libust/lttng-context-vtid.c
+++ b/libust/lttng-context-vtid.c
@@ -38,6 +38,16 @@ static inline pid_t gettid(void)
  */
 static __thread pid_t cached_vtid;
 
+/*
+ * Upon fork or clone, the TID assigned to our thread is not the same as
+ * we kept in cache. Luckily, we are the only thread surviving in the
+ * child process, so we can simply clear our cached version.
+ */
+void lttng_context_vtid_reset(void)
+{
+	cached_vtid = 0;
+}
+
 static
 size_t vtid_get_size(size_t offset)
 {
diff --git a/libust/lttng-ust-comm.c b/libust/lttng-ust-comm.c
index 6bf9e2b..7971168 100644
--- a/libust/lttng-ust-comm.c
+++ b/libust/lttng-ust-comm.c
@@ -39,6 +39,7 @@
 #include <urcu/futex.h>
 
 #include <lttng-ust-comm.h>
+#include <ust/lttng-events.h>
 #include <ust/usterr-signal-safe.h>
 #include <ust/lttng-ust-abi.h>
 #include <ust/tracepoint.h>
@@ -924,6 +925,7 @@ void ust_after_fork_child(ust_fork_info_t *fork_info)
 	/* Release urcu mutexes */
 	rcu_bp_after_fork_child();
 	lttng_ust_cleanup(0);
+	lttng_context_vtid_reset();
 	/* Release mutexes and reenable signals */
 	ust_after_fork_common(fork_info);
 	lttng_ust_init();