From: Mark Rutland > Sent: 24 September 2021 14:54 > > 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. > > 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. It ought to be something stashed in the 'wait_queue_head'. Perhaps defaulting to the address/name of the function that initialised it. That would be much nearer the original (pre Linux) semantics. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
