diff options
| author | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2017-04-06 10:28:12 -0400 |
|---|---|---|
| committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2017-04-07 09:41:51 -0400 |
| commit | 0598e4f08e3da1fea2ee3b4765a44798147a8c62 (patch) | |
| tree | 7d6875f6d550e9571b88e8f0302cb9b895f74880 /kernel/trace/Kconfig | |
| parent | 696ced4fb1d76802f864d8848aa4716633f83c17 (diff) | |
ftrace: Add use of synchronize_rcu_tasks() with dynamic trampolines
The function tracer needs to be more careful than other subsystems when it
comes to freeing data. Especially if that data is actually executable code.
When a single function is traced, a trampoline can be dynamically allocated
which is called to jump to the function trace callback. When the callback is
no longer needed, the dynamic allocated trampoline needs to be freed. This
is where the issues arise. The dynamically allocated trampoline must not be
used again. As function tracing can trace all subsystems, including
subsystems that are used to serialize aspects of freeing (namely RCU), it
must take extra care when doing the freeing.
Before synchronize_rcu_tasks() was around, there was no way for the function
tracer to know that nothing was using the dynamically allocated trampoline
when CONFIG_PREEMPT was enabled. That's because a task could be indefinitely
preempted while sitting on the trampoline. Now with synchronize_rcu_tasks(),
it will wait till all tasks have either voluntarily scheduled (not on the
trampoline) or goes into userspace (not on the trampoline). Then it is safe
to free the trampoline even with CONFIG_PREEMPT set.
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/Kconfig')
| -rw-r--r-- | kernel/trace/Kconfig | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index d4a06e714645..67b463b4f169 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -134,7 +134,8 @@ config FUNCTION_TRACER select KALLSYMS select GENERIC_TRACER select CONTEXT_SWITCH_TRACER - select GLOB + select GLOB + select TASKS_RCU if PREEMPT help Enable the kernel to trace every kernel function. This is done by using a compiler feature to insert a small, 5-byte No-Operation |