On Fri, Sep 24, 2021 at 02:54:24PM +0100, Mark Rutland wrote: > On Thu, Sep 23, 2021 at 06:16:16PM -0700, Kees Cook wrote: > > On Thu, Sep 23, 2021 at 05:22:30PM -0700, Vito Caputo wrote: > > > Instead of unwinding stacks maybe the kernel should be sticking an > > > entrypoint address in the current task struct for get_wchan() to > > > access, whenever userspace enters the kernel? > > > > wchan is supposed to show where the kernel is at the instant the > > get_wchan() happens. (i.e. recording it at syscall entry would just > > always show syscall entry.) > > It's supposed to show where a blocked task is blocked; the "wait > channel". > > I'd wanted to remove get_wchan since it requires cross-task stack > walking, which is generally painful. Right -- this is the "fragile" part I'm worried about. > We could instead have the scheduler entrypoints snapshot their caller > into a field in task_struct. If there are sufficiently few callers, that > could be an inline wrapper that passes a __func__ string. Otherwise, we > still need to symbolize. Hmm. Does PREEMPT break this? Can we actually use __builtin_return_address(0) in __schedule? -- Kees Cook
