Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 4 Feb 2021 14:10:36 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Will Deacon <will@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Matt Morehouse <mascasa@google.com>
Subject: Re: Process-wide watchpoints
Message-ID: <YBvyTDR+q0M62vKR@hirez.programming.kicks-ass.net>
References: <CACT4Y+ZsKXfAxrzJGQc5mJ+QiP5sAw7zKWtciS+07qZzSf33mw@mail.gmail.com>
 <CACT4Y+YeRtOTsMQ8xxZg-=nbv+yuJvYYhBErT46M8jtSHmiw6g@mail.gmail.com>
 <YBqXPmbpXf4hnlj3@hirez.programming.kicks-ass.net>
 <CACT4Y+a-9kqX0ZkNz-ygib+ERn41HVo_8Wx6oYMQmPjTC06j7g@mail.gmail.com>
 <YBqnAYVdNM4uyGny@hirez.programming.kicks-ass.net>
 <CACT4Y+btOt5QFKH9Q=81EnpDHoidJUHE2s0oZ8v65t-b__awuw@mail.gmail.com>
 <YBvAsku9OWM7KUno@hirez.programming.kicks-ass.net>
 <CACT4Y+ZLSyVMkPfh3PftEWKC1kC+o1XLxo_o6i4BiyRuPig27g@mail.gmail.com>
 <YBvj6eJR/DY2TsEB@hirez.programming.kicks-ass.net>
 <CACT4Y+a17L2pUY1kkRB_v_y3P_sbMpSLb6rVfXmGM7LkbAvj5Q@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CACT4Y+a17L2pUY1kkRB_v_y3P_sbMpSLb6rVfXmGM7LkbAvj5Q@mail.gmail.com>
Precedence: bulk

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.