diff options
| -rw-r--r-- | kernel/trace/Kconfig | 3 | ||||
| -rw-r--r-- | kernel/trace/ftrace.c | 42 |
2 files changed, 20 insertions, 25 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 diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 8efd9fe7aec0..34f63e78d661 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2808,18 +2808,28 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command) * callers are done before leaving this function. * The same goes for freeing the per_cpu data of the per_cpu * ops. - * - * Again, normal synchronize_sched() is not good enough. - * We need to do a hard force of sched synchronization. - * This is because we use preempt_disable() to do RCU, but - * the function tracers can be called where RCU is not watching - * (like before user_exit()). We can not rely on the RCU - * infrastructure to do the synchronization, thus we must do it - * ourselves. */ if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_PER_CPU)) { + /* + * We need to do a hard force of sched synchronization. + * This is because we use preempt_disable() to do RCU, but + * the function tracers can be called where RCU is not watching + * (like before user_exit()). We can not rely on the RCU + * infrastructure to do the synchronization, thus we must do it + * ourselves. + */ schedule_on_each_cpu(ftrace_sync); + /* + * When the kernel is preeptive, tasks can be preempted + * while on a ftrace trampoline. Just scheduling a task on + * a CPU is not good enough to flush them. Calling + * synchornize_rcu_tasks() will wait for those tasks to + * execute and either schedule voluntarily or enter user space. + */ + if (IS_ENABLED(CONFIG_PREEMPT)) + synchronize_rcu_tasks(); + arch_ftrace_trampoline_free(ops); if (ops->flags & FTRACE_OPS_FL_PER_CPU) @@ -5366,22 +5376,6 @@ void __weak arch_ftrace_update_trampoline(struct ftrace_ops *ops) static void ftrace_update_trampoline(struct ftrace_ops *ops) { - -/* - * Currently there's no safe way to free a trampoline when the kernel - * is configured with PREEMPT. That is because a task could be preempted - * when it jumped to the trampoline, it may be preempted for a long time - * depending on the system load, and currently there's no way to know - * when it will be off the trampoline. If the trampoline is freed - * too early, when the task runs again, it will be executing on freed - * memory and crash. - */ -#ifdef CONFIG_PREEMPT - /* Currently, only non dynamic ops can have a trampoline */ - if (ops->flags & FTRACE_OPS_FL_DYNAMIC) - return; -#endif - arch_ftrace_update_trampoline(ops); } |