On Thu, May 11, 2017 at 03:52:46PM +0200, Petr Mladek wrote: > Anyway, a crazy idea is to use the livepatch consistency model instead > of RCU to protect the function stack. The model makes sure that all > tasks, including the idle ones, were not running any patched function > (and their ftrace handlers) at some point. It should be safe > but I am not sure if it is worth it.
http://i3.kym-cdn.com/photos/images/original/000/173/580/Wat.jpg > Alternatively, it might be enough to use the probably more lightwight > solution that is used when ftrace handlers are deregistered, I mean: > > /* > * 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(); I couldn't grok the first idea, but this one sounds promising... -- Josh
