linux-kernel - Re: Process-wide watchpoints

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Message-ID: <CACT4Y+ZbWMa7zsa84dOBZ0C0Qgik2uDST+bzX=TrSU6vFXkkCQ@mail.gmail.com>
Date:   Thu, 4 Feb 2021 14:35:36 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Will Deacon <will@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Matt Morehouse <mascasa@...gle.com>
Subject: Re: Process-wide watchpoints

On Thu, Feb 4, 2021 at 2:10 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Feb 04, 2021 at 01:53:59PM +0100, Dmitry Vyukov wrote:
> > Humm... I was thinking of perf_event_open(pid == 0).
> > It does not make sense to send SIGTRAP in a remote process, because it
> > does not necessarily cooperate with us.
> >
> > But is there any problem with clone w/o CLONE_THREAD? Assuming the
> > current process has setup the signal handler, the child will have the
> > same handler and the same code/address space. So delivery of SIGTRAP
> > should work the same way in the child.
>
> Nothing should be doing CLONE_VM without CLONE_THREAD. Yes, it's
> possible, but if you do so, you get to keep the pieces IMO.
>
> Current libc either does a full clone (fork) or pthread_create,
> pthread_create does CLONE_THREAD.

I meant a different thing.
I meant that we could restrict synchronous SIGTRAP for (1)
perf_event_open(pid != 0) and (2) disable it after exec.
What is the issue here for clone without CLONE_THREAD?