Re: [PATCH 1/3] proc: Stop reporting eip and esp in /proc/PID/stat

From: Linus Torvalds
Date: Sat Oct 01 2016 - 00:22:25 EST

On Fri, Sep 30, 2016 at 7:01 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> Peter, how nasty would it be to add some lightish-weight lock that
> lets us pin a task in a non-running state? Maybe we could take the rq
> lock, do something to the task to make it sleepy (steal it off the
> queue?), unlock the lock, do whatever we're going, then take the lock
> again and put it back.

No. Don't do this. Forcing some sleeping lock in the core task state
/proc stuff is a nightmare. That thing ends up being used very heavily
under some loads. No _way_ is it ok to synchronize with the target

> Or if we had a seqlock-like thing, we could maybe arrange for
> get_wchan to abort if the task get scheduled between when it starts
> and when it finishes.

seq_lock might be ok, but do we even need it? What's the worst that
can happen? An odd symbol name showing up in a race condition? Sounds
like a non-issue to me.