[Linux-kernel-mentees] [PATCH v2] tracing: Annotate ftrace_graph_hash pointer with __rcu

[Amol Grover]

Fix following instances of sparse error
kernel/trace/ftrace.c:5664:29: error: incompatible types in comparison
kernel/trace/ftrace.c:5785:21: error: incompatible types in comparison
kernel/trace/ftrace.c:5864:36: error: incompatible types in comparison
kernel/trace/ftrace.c:5866:25: error: incompatible types in comparison

Use rcu_dereference_sched to dereference the __rcu annotated pointer.

Signed-off-by: Amol Grover <frextrite at gmail.com>
---
v2:
- Use rcu_dereference_sched instead of rcu_dereference_protected

 kernel/trace/ftrace.c | 2 +-
 kernel/trace/trace.h  | 9 ++++++---
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9bf1f2cd515e..959ded08dc13 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5596,7 +5596,7 @@ static const struct file_operations ftrace_notrace_fops = {
 
 static DEFINE_MUTEX(graph_lock);
 
-struct ftrace_hash *ftrace_graph_hash = EMPTY_HASH;
+struct ftrace_hash __rcu *ftrace_graph_hash = EMPTY_HASH;
 struct ftrace_hash *ftrace_graph_notrace_hash = EMPTY_HASH;
 
 enum graph_filter_type {
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 63bf60f79398..7253e8251f50 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -950,22 +950,25 @@ extern void __trace_graph_return(struct trace_array *tr,
 				 unsigned long flags, int pc);
 
 #ifdef CONFIG_DYNAMIC_FTRACE
-extern struct ftrace_hash *ftrace_graph_hash;
+extern struct ftrace_hash __rcu *ftrace_graph_hash;
 extern struct ftrace_hash *ftrace_graph_notrace_hash;
 
 static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace)
 {
 	unsigned long addr = trace->func;
 	int ret = 0;
+	struct ftrace_hash *hash;
 
 	preempt_disable_notrace();
 
-	if (ftrace_hash_empty(ftrace_graph_hash)) {
+	hash = rcu_dereference_sched(ftrace_graph_hash);
+
+	if (ftrace_hash_empty(hash)) {
 		ret = 1;
 		goto out;
 	}
 
-	if (ftrace_lookup_ip(ftrace_graph_hash, addr)) {
+	if (ftrace_lookup_ip(hash, addr)) {
 
 		/*
 		 * This needs to be cleared on the return functions
-- 
2.24.1