LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Mark Rutland <mark.rutland@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "mingo@kernel.org" <mingo@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"vincent.weaver@maine.edu" <vincent.weaver@maine.edu>,
	"eranian@gmail.com" <eranian@gmail.com>,
	"jolsa@redhat.com" <jolsa@redhat.com>,
	"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>
Subject: Re: [RFC][PATCH 1/3] perf: Tighten (and fix) the grouping condition
Date: Fri, 23 Jan 2015 15:02:12 +0000	[thread overview]
Message-ID: <20150123150211.GA6091@leverpostej> (raw)
In-Reply-To: <20150123125834.090683288@infradead.org>

On Fri, Jan 23, 2015 at 12:52:00PM +0000, Peter Zijlstra wrote:
> The fix from 9fc81d87420d ("perf: Fix events installation during
> moving group") was incomplete in that it failed to recognise that
> creating a group with events for different CPUs is semantically
> broken -- they cannot be co-scheduled.
> 
> Furthermore, it leads to real breakage where, when we create an event
> for CPU Y and then migrate it to form a group on CPU X, the code gets
> confused where the counter is programmed -- triggered by the fuzzer.
> 
> Fix this by tightening the rules for creating groups. Only allow
> grouping of counters that can be co-scheduled in the same context.
> This means for the same task and/or the same cpu.

It seems this would still allow you to group CPU-affine software and
uncore events, which also doesn't make sense: the software events will
count on a single CPU while the uncore events aren't really CPU-affine.

Which isn't anything against this patch, but probably something we
should tighten up too.

> 
> Fixes: 9fc81d87420d ("perf: Fix events installation during moving group")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/linux/perf_event.h |    6 ------
>  kernel/events/core.c       |   15 +++++++++++++--
>  2 files changed, 13 insertions(+), 8 deletions(-)
> 
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -450,11 +450,6 @@ struct perf_event {
>  #endif /* CONFIG_PERF_EVENTS */
>  };
>  
> -enum perf_event_context_type {
> -	task_context,
> -	cpu_context,
> -};
> -
>  /**
>   * struct perf_event_context - event context structure
>   *
> @@ -462,7 +457,6 @@ enum perf_event_context_type {
>   */
>  struct perf_event_context {
>  	struct pmu			*pmu;
> -	enum perf_event_context_type	type;
>  	/*
>  	 * Protect the states of the events in the list,
>  	 * nr_active, and the list:
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6846,7 +6846,6 @@ int perf_pmu_register(struct pmu *pmu, c
>  		__perf_event_init_context(&cpuctx->ctx);
>  		lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex);
>  		lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock);
> -		cpuctx->ctx.type = cpu_context;
>  		cpuctx->ctx.pmu = pmu;
>  
>  		__perf_cpu_hrtimer_init(cpuctx, cpu);
> @@ -7493,7 +7492,19 @@ SYSCALL_DEFINE5(perf_event_open,
>  		 * task or CPU context:
>  		 */
>  		if (move_group) {
> -			if (group_leader->ctx->type != ctx->type)
> +			/*
> +			 * Make sure we're both on the same task, or both
> +			 * per-cpu events.
> +			 */
> +			if (group_leader->ctx->task != ctx->task)
> +				goto err_context;
> +

Up to this point, this looks very similar to what I tried previously
[1], where we eventually figured out [2] that this raced with the
context switch optimisation. I never got around to fixing that race.

I'll try and get my head around that again. I'm not sure if that's still
a problem, and from a quick look at this series it's not clear that it
would be fixed if it is a problem.

Thanks,
Mark.

[1] https://lkml.org/lkml/2014/2/10/937
[2] https://lkml.org/lkml/2014/2/27/834

  reply	other threads:[~2015-01-23 15:02 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-23 12:51 [RFC][PATCH 0/3] perf fixes Peter Zijlstra
2015-01-23 12:52 ` [RFC][PATCH 1/3] perf: Tighten (and fix) the grouping condition Peter Zijlstra
2015-01-23 15:02   ` Mark Rutland [this message]
2015-01-23 15:07     ` Peter Zijlstra
2015-01-23 15:22       ` Mark Rutland
2015-02-04 12:59         ` Peter Zijlstra
2015-01-28 14:30   ` [tip:perf/urgent] " tip-bot for Peter Zijlstra
2015-01-23 12:52 ` [RFC][PATCH 2/3] perf: Add a bit of paranoia Peter Zijlstra
2015-01-26 16:26   ` Peter Zijlstra
2015-01-27 21:28     ` Vince Weaver
2015-01-29  2:16       ` Vince Weaver
2015-01-29  7:51         ` Jiri Olsa
2015-01-29 13:44           ` Peter Zijlstra
2015-02-04 14:39             ` [tip:perf/core] perf: Fix put_event() ctx lock tip-bot for Peter Zijlstra
2015-01-29 14:47     ` [RFC][PATCH 2/3] perf: Add a bit of paranoia Peter Zijlstra
2015-02-02  6:33       ` Vince Weaver
2015-02-02 15:42         ` Peter Zijlstra
2015-02-02 17:32           ` Peter Zijlstra
2015-02-04 14:51             ` Jiri Olsa
2015-02-04 16:33               ` Peter Zijlstra
2015-02-04 16:43                 ` Peter Zijlstra
2015-02-04 14:39     ` [tip:perf/core] perf: Fix move_group() order tip-bot for Peter Zijlstra (Intel)
2015-02-04 14:39   ` [tip:perf/core] perf: Add a bit of paranoia tip-bot for Peter Zijlstra
2015-01-23 12:52 ` [RFC][PATCH 3/3] perf: Fix event->ctx locking Peter Zijlstra
2015-02-04 14:39   ` [tip:perf/core] " tip-bot for Peter Zijlstra
2015-01-26 14:30 ` [RFC][PATCH 0/3] perf fixes Vince Weaver
2015-01-26 18:03   ` Vince Weaver
2015-01-26 18:34     ` Jiri Olsa
2015-01-26 18:52       ` Vince Weaver

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20150123150211.GA6091@leverpostej \
    --to=mark.rutland@arm.com \
    --cc=eranian@gmail.com \
    --cc=jolsa@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --cc=vincent.weaver@maine.edu \
    --subject='Re: [RFC][PATCH 1/3] perf: Tighten (and fix) the grouping condition' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).