On Wed, May 11, 2022 at 04:33:57PM +0000, Song Liu wrote: > >> Ideally we'd have the ORC unwinder for all arches, that would make this > >> much easier. But we're not there yet. > > > > The alternative solution is that the process has to migrate itself > > on some safe location. > > > > One crazy idea. It still might be possible to find the called > > functions on the stack even when it is not reliable. Then it > > might be possible to add another ftrace handler on > > these found functions. This other ftrace handler might migrate > > the task when it calls this function again. > > > > It assumes that the task will call the same functions again > > and again. Also it might require that the tasks checks its > > own stack from the ftrace handler. I am not sure if this > > is possible. > > > > There might be other variants of this approach. > > This might be the ultimate solution! As ftrace allows filtering based > on pid (/sys/kernel/tracing/set_ftrace_pid), we can technically trigger > klp_try_switch_task() on every function of the pending tasks. If this > works, we should finish most of the transition in seconds. And the only > failure there would be threads with being patched function at the very > sottom of its stack. Am I too optimistic here? It's a crazy idea, but I kind of like it ;-) Especially this variant of tracing all functions for the task. We'd have to make sure unwinding from an ftrace handler works for all arches/unwinders. -- Josh
