Document limitation of vppid and ppid context wrt eventual RCU instrumentation

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

diff --git a/lttng-context-ppid.c b/lttng-context-ppid.c
index 058190484d75350ab181f9096e9f20a1e295a3d0..58ff3fe719200bf9c8bf964feb47eb72e5f65c4d 100644 (file)
--- a/lttng-context-ppid.c
+++ b/lttng-context-ppid.c
@@ -46,6 +46,15 @@ void ppid_record(struct lttng_ctx_field *field,
 {
        pid_t ppid;
 
+
+       /*
+        * TODO: when we eventually add RCU subsystem instrumentation,
+        * taking the rcu read lock here will trigger RCU tracing
+        * recursively. We should modify the kernel synchronization so
+        * it synchronizes both for RCU and RCU sched, and rely on
+        * rcu_read_lock_sched_notrace.
+        */
+
        rcu_read_lock();
        ppid = task_tgid_nr(current->real_parent);
        rcu_read_unlock();

diff --git a/lttng-context-vppid.c b/lttng-context-vppid.c
index 365d97394e89c98094b43dacc5918ee353271c00..06377a3098ff7f72b992f0c9848f693fbc10f7dc 100644 (file)
--- a/lttng-context-vppid.c
+++ b/lttng-context-vppid.c
@@ -51,6 +51,15 @@ void vppid_record(struct lttng_ctx_field *field,
         * current nsproxy can be NULL when scheduled out of exit. pid_vnr uses
         * the current thread nsproxy to perform the lookup.
         */
+
+       /*
+        * TODO: when we eventually add RCU subsystem instrumentation,
+        * taking the rcu read lock here will trigger RCU tracing
+        * recursively. We should modify the kernel synchronization so
+        * it synchronizes both for RCU and RCU sched, and rely on
+        * rcu_read_lock_sched_notrace.
+        */
+
        rcu_read_lock();
        parent = rcu_dereference(current->real_parent);
        if (!current->nsproxy)