linux-kernel - Re: [PATCH v3 07/11] perf: Add breakpoint information to siginfo on SIGTRAP

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Date:   Wed, 24 Mar 2021 14:43:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     alexander.shishkin@...ux.intel.com, acme@...nel.org,
        mingo@...hat.com, jolsa@...hat.com, mark.rutland@....com,
        namhyung@...nel.org, tglx@...utronix.de, glider@...gle.com,
        viro@...iv.linux.org.uk, arnd@...db.de, christian@...uner.io,
        dvyukov@...gle.com, jannh@...gle.com, axboe@...nel.dk,
        mascasa@...gle.com, pcc@...gle.com, irogers@...gle.com,
        kasan-dev@...glegroups.com, linux-arch@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 07/11] perf: Add breakpoint information to siginfo on
 SIGTRAP

On Wed, Mar 24, 2021 at 02:21:37PM +0100, Peter Zijlstra wrote:
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5652,13 +5652,17 @@ static long _perf_ioctl(struct perf_even
>  		return perf_event_query_prog_array(event, (void __user *)arg);
>  
>  	case PERF_EVENT_IOC_MODIFY_ATTRIBUTES: {
> +		struct perf_event_attr __user *uattr;
>  		struct perf_event_attr new_attr;
> -		int err = perf_copy_attr((struct perf_event_attr __user *)arg,
> -					 &new_attr);
> +		int err;
>  
> +		uattr = (struct perf_event_attr __user *)arg;
> +		err = perf_copy_attr(uattr, &new_attr);
>  		if (err)
>  			return err;
>  
> +		event->siginfo.si_perf = (unsigned long)uattr;

Oh bugger; that wants updating for all children too..

> +
>  		return perf_event_modify_attr(event,  &new_attr);
>  	}
>  	default:
> @@ -12011,6 +12010,11 @@ SYSCALL_DEFINE5(perf_event_open,
>  		goto err_task;
>  	}
>  
> +	clear_siginfo(&event->siginfo);
> +	event->siginfo.si_signo = SIGTRAP;
> +	event->siginfo.si_code = TRAP_PERF;
> +	event->siginfo.si_perf = (unsigned long)attr_uptr;

And inherit_event() / perf_event_alloc() want to copy/propagate that.

>  	if (is_sampling_event(event)) {
>  		if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
>  			err = -EOPNOTSUPP;