tracing: Clean up access to trace_event_file from a file pointer

The tracing code provides two functions event_file_file() and
event_file_data() to obtain a trace_event_file pointer from a file struct.
The primary method to use is event_file_file(), as it checks for the
EVENT_FILE_FL_FREED flag to determine whether the event is being removed.
The second function event_file_data() is an optimization for retrieving the
same data when the event_mutex is still held.

In the past, when removing an event directory in remove_event_file_dir(),
the code set i_private to NULL for all event files and readers were
expected to check for this state to recognize that the event is being
removed. In the case of event_id_read(), the value was read using
event_file_data() without acquiring the event_mutex. This required
event_file_data() to use READ_ONCE() when retrieving the i_private data.

With the introduction of eventfs, i_private is assigned when an eventfs
inode is allocated and remains set throughout its lifetime.

Remove the now unnecessary READ_ONCE() access to i_private in both
event_file_file() and event_file_data(). Inline the access to i_private in
remove_event_file_dir(), which allows event_file_data() to handle i_private
solely as a trace_event_file pointer. Add a check in event_file_data() to
ensure that the event_mutex is held and that file->flags doesn't have the
EVENT_FILE_FL_FREED flag set. Finally, move event_file_data() immediately
after event_file_code() since the latter provides a comment explaining how
both functions should be used together.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Link: https://patch.msgid.link/20260219162737.314231-5-petr.pavlu@suse.com
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

2 files changed, 14 insertions, 9 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b8f3804586a0..7db78a62f786 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1802,11 +1802,6 @@ extern struct trace_event_file *find_event_file(struct trace_array *tr,
 						const char *system,
 						const char *event);
 
-static inline void *event_file_data(struct file *filp)
-{
-	return READ_ONCE(file_inode(filp)->i_private);
-}
-
 extern struct mutex event_mutex;
 extern struct list_head ftrace_events;
 
@@ -1827,12 +1822,22 @@ static inline struct trace_event_file *event_file_file(struct file *filp)
 	struct trace_event_file *file;
 
 	lockdep_assert_held(&event_mutex);
-	file = READ_ONCE(file_inode(filp)->i_private);
+	file = file_inode(filp)->i_private;
 	if (!file || file->flags & EVENT_FILE_FL_FREED)
 		return NULL;
 	return file;
 }
 
+static inline void *event_file_data(struct file *filp)
+{
+	struct trace_event_file *file;
+
+	lockdep_assert_held(&event_mutex);
+	file = file_inode(filp)->i_private;
+	WARN_ON(!file || file->flags & EVENT_FILE_FL_FREED);
+	return file;
+}
+
 extern const struct file_operations event_trigger_fops;
 extern const struct file_operations event_hist_fops;
 extern const struct file_operations event_hist_debug_fops;
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 26d1e95a55d1..6523c873689a 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2184,12 +2184,12 @@ static int trace_format_open(struct inode *inode, struct file *file)
 static ssize_t
 event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
 {
-	int id = (long)event_file_data(filp);
+	/* id is directly in i_private and available for inode's lifetime. */
+	int id = (long)file_inode(filp)->i_private;
 	char buf[32];
 	int len;
 
-	if (unlikely(!id))
-		return -ENODEV;
+	WARN_ON(!id);
 
 	len = sprintf(buf, "%d\n", id);