perf thread: Ensure comm_lock held for comm_list

Add thread safety annotations for comm_list and add locking for two
instances where the list is accessed without the lock held (in
contradiction to ____thread__set_comm()).

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250529192206.971199-1-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Author: captain5050

tools/perf/util/comm.c

@@ -24,6 +24,7 @@ static struct comm_strs {
 static void comm_strs__remove_if_last(struct comm_str *cs);
 
 static void comm_strs__init(void)
+	NO_THREAD_SAFETY_ANALYSIS /* Inherently single threaded due to pthread_once. */
 {
 	init_rwsem(&_comm_strs.lock);
 	_comm_strs.capacity = 16;
@@ -119,6 +120,7 @@ static void comm_strs__remove_if_last(struct comm_str *cs)
 }
 
 static struct comm_str *__comm_strs__find(struct comm_strs *comm_strs, const char *str)
+	SHARED_LOCKS_REQUIRED(comm_strs->lock)
 {
 	struct comm_str **result;
 

tools/perf/util/thread.c

@@ -41,6 +41,7 @@ int thread__init_maps(struct thread *thread, struct machine *machine)
 }
 
 struct thread *thread__new(pid_t pid, pid_t tid)
+	NO_THREAD_SAFETY_ANALYSIS /* Allocation/creation is inherently single threaded. */
 {
 	RC_STRUCT(thread) *_thread = zalloc(sizeof(*_thread));
 	struct thread *thread;
@@ -200,24 +201,39 @@ int thread__set_namespaces(struct thread *thread, u64 timestamp,
 	return ret;
 }
 
-struct comm *thread__comm(struct thread *thread)
+static struct comm *__thread__comm(struct thread *thread)
+	SHARED_LOCKS_REQUIRED(thread__comm_lock(thread))
 {
 	if (list_empty(thread__comm_list(thread)))
 		return NULL;
 
 	return list_first_entry(thread__comm_list(thread), struct comm, list);
 }
 
+struct comm *thread__comm(struct thread *thread)
+{
+	struct comm *res = NULL;
+
+	down_read(thread__comm_lock(thread));
+	res = __thread__comm(thread);
+	up_read(thread__comm_lock(thread));
+	return res;
+}
+
 struct comm *thread__exec_comm(struct thread *thread)
 {
 	struct comm *comm, *last = NULL, *second_last = NULL;
 
+	down_read(thread__comm_lock(thread));
 	list_for_each_entry(comm, thread__comm_list(thread), list) {
-		if (comm->exec)
+		if (comm->exec) {
+			up_read(thread__comm_lock(thread));
 			return comm;
+		}
 		second_last = last;
 		last = comm;
 	}
+	up_read(thread__comm_lock(thread));
 
 	/*
 	 * 'last' with no start time might be the parent's comm of a synthesized
@@ -233,8 +249,9 @@ struct comm *thread__exec_comm(struct thread *thread)
 
 static int ____thread__set_comm(struct thread *thread, const char *str,
 				u64 timestamp, bool exec)
+	EXCLUSIVE_LOCKS_REQUIRED(thread__comm_lock(thread))
 {
-	struct comm *new, *curr = thread__comm(thread);
+	struct comm *new, *curr = __thread__comm(thread);
 
 	/* Override the default :tid entry */
 	if (!thread__comm_set(thread)) {
@@ -285,8 +302,9 @@ int thread__set_comm_from_proc(struct thread *thread)
 }
 
 static const char *__thread__comm_str(struct thread *thread)
+	SHARED_LOCKS_REQUIRED(thread__comm_lock(thread))
 {
-	const struct comm *comm = thread__comm(thread);
+	const struct comm *comm = __thread__comm(thread);
 
 	if (!comm)
 		return NULL;

tools/perf/util/thread.h

@@ -236,14 +236,15 @@ static inline struct rw_semaphore *thread__namespaces_lock(struct thread *thread
 	return &RC_CHK_ACCESS(thread)->namespaces_lock;
 }
 
-static inline struct list_head *thread__comm_list(struct thread *thread)
+static inline struct rw_semaphore *thread__comm_lock(struct thread *thread)
 {
-	return &RC_CHK_ACCESS(thread)->comm_list;
+	return &RC_CHK_ACCESS(thread)->comm_lock;
 }
 
-static inline struct rw_semaphore *thread__comm_lock(struct thread *thread)
+static inline struct list_head *thread__comm_list(struct thread *thread)
+	SHARED_LOCKS_REQUIRED(thread__comm_lock(thread))
 {
-	return &RC_CHK_ACCESS(thread)->comm_lock;
+	return &RC_CHK_ACCESS(thread)->comm_list;
 }
 
 static inline u64 thread__db_id(const struct thread *thread)