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. Signed-off-by: Petr Pavlu <[email protected]> --- kernel/trace/trace.h | 17 +++++++++++------ kernel/trace/trace_events.c | 6 +++--- 2 files changed, 14 insertions(+), 9 deletions(-) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 8428c437cb9d..27fb3fe6a7e0 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; diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 2ca76b048638..d23e7a9d07e6 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -2090,12 +2090,12 @@ 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); -- 2.52.0
