Messages in this thread | | | From | Dmitry Vyukov <> | Date | Thu, 4 Feb 2021 14:37:21 +0100 | Subject | Re: Process-wide watchpoints |
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On Thu, Feb 4, 2021 at 2:33 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Thu, Feb 04, 2021 at 01:53:59PM +0100, Dmitry Vyukov wrote: > > On Thu, Feb 4, 2021 at 1:09 PM Peter Zijlstra <peterz@infradead.org> wrote: > > > > What do we do then? The advantage of IOC_REFRESH is that it disables the > > > event until it gets explicitly re-armed, avoiding recursion issues etc. > > > Do you want those semantics? If so, we'd need to have IOC_REFRESH find > > > the actual event for the current task, which should be doable I suppose. > > > > Frankly, I don't know. I didn't use it in my prototype, nor I fully > > understand what it's doing. Does it make sense for breakpoints? > > I see IOC_REFRESH has a check for !attr.inherit, so it will fail for > > my use case currently. I would say we just leave it as is for now. > > Well, the way it works is that currently you set event_limit > 0. Then > each event will decrement, when we hit 0 we disable and raise a signal. > > REFRESH will increment event_limit and re-enable. > > This means you're guaranteed not to get another signal until you're > ready for it. It allows leaving the signal handler context to handle the > signal. > > I suppose you're looking for something like this, which goes in top of > that thread_only thing. > > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -389,7 +389,8 @@ struct perf_event_attr { > cgroup : 1, /* include cgroup events */ > text_poke : 1, /* include text poke events */ > thread_only : 1, /* only inherit on threads */ > - __reserved_1 : 29; > + sigtrap : 1, /* foo */ > + __reserved_1 : 28; > > union { > __u32 wakeup_events; /* wakeup every n events */ > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -6273,6 +6273,13 @@ static void perf_pending_event_disable(s > > if (cpu == smp_processor_id()) { > WRITE_ONCE(event->pending_disable, -1); > + > + if (event->attr.sigtrap) { > + atomic_inc(&event->event_limit); /* rearm */ > + send_sig_info(SIGTRAP, SEND_SIG_PRIV, current); > + return; > + } > + > perf_event_disable_local(event); > return; > } > @@ -8936,6 +8943,7 @@ static int __perf_event_overflow(struct > int throttle, struct perf_sample_data *data, > struct pt_regs *regs) > { > + perf_overflow_handler_t ovf; > int events = atomic_read(&event->event_limit); > int ret = 0; > > @@ -8961,7 +8969,15 @@ static int __perf_event_overflow(struct > perf_event_disable_inatomic(event); > } > > - READ_ONCE(event->overflow_handler)(event, data, regs); > + ovf = READ_ONCE(event->overflow_handler); > +#ifdef CONFIG_RETPOLINE > + if (ovf == perf_event_output_forward) { > + perf_event_output_forward(event, data, regs); > + } else if (ovf == perf_event_output_backward) { > + perf_event_output_backward(event, data, regs); > + } else > +#endif > + ovf(event, data, regs); > > if (*perf_event_fasync(event) && event->pending_kill) { > event->pending_wakeup = 1; > @@ -11281,6 +11297,9 @@ perf_event_alloc(struct perf_event_attr > > event->state = PERF_EVENT_STATE_INACTIVE; > > + if (event->attr.sigtrap) > + event->event_limit = ATOMIC_INIT(1); > + > if (task) { > event->attach_state = PERF_ATTACH_TASK; > /* > @@ -11556,6 +11575,9 @@ static int perf_copy_attr(struct perf_ev > if (attr->thread_only && !attr->inherit) > return -EINVAL; > > + if (attr->sigtrap && attr->inherit && !attr->thread_only) > + return -EINVAL; > + > out: > return ret;
Thanks. Let me see if this will work for us and test.
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