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. A previous fix also modified event_id_read() to read i_private while holding the event_mutex. Remove the now unnecessary READ_ONCE() access to i_private in both event_file_file() and event_file_data(). 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. Signed-off-by: Petr Pavlu <[email protected]> --- kernel/trace/trace.h | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index c11edec5d8f5..c6b450de93bc 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -1739,11 +1739,6 @@ 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; @@ -1764,12 +1759,22 @@ 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; -- 2.52.0
