linux-kernel - Re: Process-wide watchpoints

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Message-ID: <CACT4Y+a-9kqX0ZkNz-ygib+ERn41HVo_8Wx6oYMQmPjTC06j7g@mail.gmail.com>
Date:   Wed, 3 Feb 2021 13:49:56 +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 Wed, Feb 3, 2021 at 1:29 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Feb 01, 2021 at 09:50:20AM +0100, Dmitry Vyukov wrote:
> > Or, alternatively would it be reasonable for perf to generate SIGTRAP
> > directly on watchpoint hit (like ptrace does)? That's what I am
> > ultimately trying to do by attaching a bpf program.
>
> Perf should be able to generate signals, The perf_event_open manpage
> lists two ways of trigering signals. The second way doesn't work for
> you, due to it not working on inherited counters, but would the first
> work?
>
> That is, set attr::wakeup_events and fcntl(F_SETSIG).

The problem is that this sends a signal to the fd owner rather than
the thread that hit the breakpoint. At least that's what happened in
our tests. We would like to send a signal to the thread that hit the
breakpoint.