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

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Message-ID: <CA+55aFxZkzC4uCXgL3BEGbbobtm0-n8FoNnswx5s=+8PNsGo2w@mail.gmail.com>
Date:   Fri, 30 Sep 2016 21:22:08 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Jann Horn <jann@...jh.net>, Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Tycho Andersen <tycho.andersen@...onical.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [PATCH 1/3] proc: Stop reporting eip and esp in /proc/PID/stat

On Fri, Sep 30, 2016 at 7:01 PM, Andy Lutomirski <luto@...capital.net> 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
task.

> 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.

        Linus