linux-kernel - Re: [PATCH] perf/core: fix group {cpu,task} validation

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Message-ID: <20170821155326.bbmpn62rcr64274p@hirez.programming.kicks-ass.net>
Date:   Mon, 21 Aug 2017 17:53:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Zhou Chengming <zhouchengming1@...wei.com>
Subject: Re: [PATCH] perf/core: fix group {cpu,task} validation

On Thu, Jun 22, 2017 at 03:41:38PM +0100, Mark Rutland wrote:
> Regardless of which events form a group, it does not make sense for the
> events to target different tasks and/or CPUs, as this leaves the group
> inconsistent and impossible to schedule. The core perf code assumes that
> these are consistent across (successfully intialised) groups.
> 
> Core perf code only verifies this when moving SW events into a HW
> context. Thus, we can violate this requirement for pure SW groups and
> pure HW groups, unless the relevant PMU driver happens to perform this
> verification itself. These mismatched groups subsequently wreak havoc
> elsewhere.
> 
> For example, we handle watchpoints as SW events, and reserve watchpoint
> HW on a per-cpu basis at pmu::event_init() time to ensure that any event
> that is initialised is guaranteed to have a slot at pmu::add() time.
> However, the core code only checks the group leader's cpu filter (via
> event_filter_match()), and can thus install follower events onto CPUs
> violating thier (mismatched) CPU filters, potentially installing them
> into a CPU without sufficient reserved slots.
> 

> 
> Fix this by validating this requirement regardless of whether we're
> moving events.

Yes, and this also appears to cure your other problem:

  https://lkml.kernel.org/r/20170810173551.GD12812@leverpostej


Thanks!