From: "Steven Rostedt (Red Hat)" Passing data to the function callback was originally done by adding the ftrace_ops in another structure, and using the container_of() to get the field. But this adds a bit more complexity than it is worth, and adding a simple .private field to ftrace_ops makes things a lot easier. But be warned, the .private data should not be freed once it is used unless the ftrace_ops itself has gone through the necessary freeing routines. A simple synchronize_sched() is not enough as functions can be traced that are called outside the view of RCU and all its concoctions. Signed-off-by: Steven Rostedt --- include/linux/ftrace.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index f4233b1..ef1607e 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -105,11 +105,23 @@ enum { FTRACE_OPS_FL_INITIALIZED = 1 << 8, }; +/* + * Note, ftrace_ops can be referenced outside of RCU protection. + * (Although, for perf, the control ops prevent that). If ftrace_ops is + * allocated and not part of kernel core data, the unregistering of it will + * perform a scheduling on all CPUs to make sure that there are no more users. + * Depending on the load of the system that may take a bit of time. + * + * Any private data added must also take care not to be freed and if private + * data is added to a ftrace_ops that is in core code, the user of the + * ftrace_ops must perform a schedule_on_each_cpu() before freeing it. + */ struct ftrace_ops { ftrace_func_t func; struct ftrace_ops *next; unsigned long flags; int __percpu *disabled; + void *private; #ifdef CONFIG_DYNAMIC_FTRACE struct ftrace_hash *notrace_hash; struct ftrace_hash *filter_hash; -- 1.8.5.3