Re: Process-wide watchpoints

[Peter Zijlstra]

On Wed, Feb 03, 2021 at 01:49:56PM +0100, Dmitry Vyukov wrote:
> On Wed, Feb 3, 2021 at 1:29 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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.

Ah indeed.. all of this was aimed at self-monitoring.

Letting perf send a signal to the monitored task is intrusive.. let me
think on that.